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    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Events August 2011: Join ‘Dawn’ and visit the brightest asteroid, Vesta!

NASA simulation of Dawn spacecraft arriving to orbit Vesta.

Latest News: Dawn’s “Smooth Move”  – with the latest pictureYour  Mission to Vesta

As August begins, the mission of Dawn, a US spacecraft launched four years ago,  is at its first peak, as the spacecraft knuckles down to a year-long orbit of the brightest asteroid, Vesta. We’ll be treated this month to lots of close-up images – and some serious science data reflecting on the very beginnings of our solar system – but why not visit Vesta yourself?  Using ordinary binoculars it is easily seen as a star-like object in our southeastern skies around midnight. Recording  the asteroid’s looping path for the next three months will help build your  star-finding skills and improve your knowledge of the night sky.  Meanwhile, Dawn will continue to orbit Vesta right through to next July when it breaks away and heads for its second target, the dwarf planet Ceres, which Dawn is due to reach in the winter of 2015. (Its mission started in September of 2007.)

Here’s a time lapse movie simulation showing Vesta at one-day intervals from August 1 to early November 2011.  It traces Vesta’s path against the background stars of Capricornus – what I call the “Arrowhead”  asterism – and shows how the asteroid changes, growing dimmer as it appears to stop and reverse direction.  Look closely at the video – Vesta is the little dot that moves!  Click the full screen option in the lower right corner under the video – that will give you a much better view.  And don’t worry, there are more detailed charts and instructions to help you find Vesta – this just gives you a general idea of where it is , and how much it moves over three months.

Of course, some of the more knowledgeable night sky watchers may wonder why I’m not featuring the wonderful Perseid meteor shower this month. The reason is simple: The  nearly full Moon is going to eat up all but the very brightest meteors. Still, if you happen to be enjoying the Moon on the nights of August 11 or 12th, don’t be surprised if a few bright Perseids burn their way through the glare! But this is not the year to get a good view of this favorite shower. We do have Saturn riding off into the sunset as Jupiter slowly makes its way from the morning sky to more convenient evening viewing hours – and Mars is well placed well before dawn. You’ll find details on observing these planets here.

Your Mission to Vesta

Got your 3D glasses handy? Even if not, this close-up from Dawn cameras gives you a good idea of what this piece of a planet wannabee looks like! At 330 miles it's the largest asteroid, now that Ceres, nearly twice its size, is classified as a dwarf planet.

The real astral satisfaction this month comes from tracking down Vesta.  A nice project is to print out your own chart and record Vesta’s position on several different nights as observing conditions permit. How fast it moves from night to night tells you something about how relatively close it is to us, and that loop it makes (see video) marks the fact that the Earth overtakes and passes it, since our orbit is shorter and we’re moving faster. When we first see Vesta it is in retrograde (east to west) motion against the background of stars.  But in early September it will nearly come to  a halt before resuming its normal eastward path among the stars and heading back very close to the point we saw it on August 1. In the process, it will have two very close encounters with a 4th magnitude star, Psi (Ψ) Capricorni.

Here are several charts showing Vesta’s path. It is actually bright enough this month to see with the naked eye. But for that you would need both good eyesight and skies pretty much free of light pollution. For most of us, though, it will be an easy target using binoculars, and the best time to look will be around midnight when it’s about as high as it gets just east of south.  Digging one little star-like dot out of a dim section of sky is always a fun challenge.  Think of being the first to discover that this dim star moved! Oh the excitement that must have caused back in 1807!

First, the big view!

OK – let’s start with a finder chart showing the general region. There’s just one bright guidepost star in this area of sky, Fomalhaut, and you can use that as a starting point. The easiest asterism to see is the Teapot in the southwest. The “Arrowhead” asterism – the constellation Capricornus – holds Vesta, but consists mainly of fourth and fifth magnitude stars – visible, but dim, much like the fainter stars of the Little Dipper. I’ve included the general positions of Ceres (which we’ll examine in detail next month when it’s brighter and higher in the sky) and Neptune, which hasn’t moved much from where you may have found it in July.  (See detailed Neptune charts here.)

This general region of the sky contains only one really bright star - Fomalhaut. Besides our target this month, Vesta, it also contains Neptune - the main subject of last month's events column, and the dwarf planet Ceres, which will be a focus in September when it reaches its brightest stage. Click image for much larger version. (Created from Starry Nights Pro screen shot.)

Zooming in on the “Arrowhead”  and Vesta, here’s what we can expect.  Click on the  image for a much larger version. Note – numbers in parentheses are magnitudes with the period omitted to avoid confusion with stars. Thus Vesta’s magnitude on August 1 is 5.7. The green circle represents a seven degree field of view, typical for low power binoculars. (Similar charts will be published next month for September and October.)

Vesta's path in August. Note - numbers in parentheses are magnitudes with the period omitted to avoid confusion with stars. Thus Vesta's magnitude on August 1 is 5.7. The green circle represents a seven degree field of view, typical for low power binoculars. The magnitude of key stars are given to help you distinguish them from Vesta. Click image a for much larger version. Vesta should be easiest to find at the end of the month when for three nights it is very close to Psi Capricorni, a 4th magnitude star. The August 6th position is noted because that's when Vesta is at "opposition" - rising in the east as the sun sets in the west - and at its brightest.

Printer-friendly version of this chart

This same chart can be used to trace the path of Vesta during September and October as well. That’s because Vesta continues moving west for only about one degree past Psi (Ψ) Capricorni. By the middle of September it will appear to slow down, stay in one place for a few days, then start back-tracking quite close to the path it has been following.  So click here to download a printer-friendly (black on white) version of this chart that you can use to record your own observations of Vesta.

 Vesta and other asteroids

This composite image shows the comparative sizes of nine asteroids. Vesta dwarfs all other small bodies in this image. Asteroid Vesta also is considered a protoplanet because it's a large body that almost became a planet and has a diameter of approximately 330 miles (530 kilometers). Caption and image from: NASA/JPL-Caltech/JAXA/ESA (Click image for larger version.)

Asteroids are pieces of  a planet that never formed. As such they are examples of the raw materials form which other planets have formed.

Asteroids are concentrated in the Asteroid Belt between Mars and Jupiter – but they can actually be found throughout the area inhabited by the planets.

Asteroids tend to be quite porous, making it difficult to estimate their density and thus their gravity. In fact, scientists could not predict exactly when the Dawn spacecraft would go into orbit around Vesta because they were unsure of Vesta’s gravitational pull – though Dawn should give them much more precise information on Vesta’s gravity now that it is in orbit.

Ida and Dactyl - NASA photo.

More than 100 asteroids have moons! The first was discovered on August 28, 1993, when the Galileo spacecraft flew within 1500 miles of the asteroid 243 Ida.  The tiny moon, less than a mile across, was dubbed Dactyl.

The first asteroid discovered was Ceres, now considered a dwarf planet.  It was discovered in 1801 by Sicilian astronomer Giuseppe Piazza during a search for a planet believed to be between Mars and Jupiter.  The planet was never found and Ceres, though almost twice as large as Vesta, was judged to be too small to be a planet.  The extra bulk of Ceres allowed it to form as something close to a sphere – a distinction that makes it a dwarf planet. However, it is not large enough to have gobbled up  other small objects in its neighborhood as a true planet would do. The best known dwarf planet is, of course, Pluto.

Though Vesta is smaller than Ceres,  it is closer to us and has a more reflective surface, so it appears significantly brighter.

In binoculars and most telescopes asteroids appear as dots, just like stars. It takes the Hubble Space telescope – or better yet,  a spacecraft  – to really see what they look like.

During the early years of the solar system, asteroids appear to have engaged in a game of celestial bumper cars. The result is there are many, many more small ones than large ones – and some appear to be just loosely bonded rubble heaps.

Such asteroid collisions still can happen, and just last year the Hubble Space Telescope captured pictures of what certainly seems to be such a collision. See the images and read about it here.

Asteroids are similar to comets, but unlike comets they do not give off gas and dust as they get near the Sun.

The two small moons of Mars are believed to be captured asteroids, as are many of the irregular moons of the Gas Giants – the four outer planets.

For many years asteroids were known simply as small planets in France and Germany (petit or kleine), though in England they were called “Minor Planets.” Only in America were they called asteroids, the term now adopted by international agreement.

Oh – some will tell you Vesta is not the brightest asteroid and technically they are right. There is one that will come quite close to Earth – when first discovered they thought it might actually hit us – in 2029. On that close approach it will be third magnitude – easily visible to the naked eye.  But since this is a brief event, and we regularly see Vesta, Vesta is still the brightest for all practical concerns.

And yes, asteroids colliding with the Earth are still a scary prospect, though in the past decade they have done a wonderful job of locating  – and ruling out  – most of the ones that might prove a threat. But there’s a lot of space and a lot of chunks of rock, so the search goes on.

The Dawn Mission to Vesta

Stepping onto my soapbox: I wish we would pat ourselves on the back more often and with more vigor. The Dawn Mission  to Vesta and Ceres  is an incredible accomplishment of science and technology resulting from a long and successful collaboration between government, private industry, and academe. It is absolutely fantastic that we can invent robots such as this, build them, and ship them off on a mission nearly a decade long to find and orbit what are really two very small specks of dust in the vast empty space of our solar system.  It deserves a lot more attention than the media gives it and all of us should take a lot more pride in its success!

Whew! OK – down off my soapbox. If you really want a feel for the complete Dawn mission, watch this NASA video – though it’s a bit long, so be patient.

http://video.google.com/googleplayer.swf?docid=-5412000236766165719&hl=en&fs=true

And here’s how NASA sums up the mission:

The top level question that the mission addresses is the role of size and water in determining the evolution of the planets. Ceres and Vesta are the right two bodies with which to address this question, as they are the most massive of the protoplanets, baby planets whose growth was interrupted by the formation of Jupiter. Ceres is very primitive and wet while Vesta is evolved and dry. The instrumentation to be flown is complete, flight-proven and similar to that used for Mercury, Mars, the Moon, Eros and comets. The science team consists of leading experts in the investigation of the rocky and icy planets using proven measurement and analysis techniques.

Vesta shape model overlaid with a false texture maps

Dawn has the potential for making many paradigm-shifting discoveries. Ceres may have active hydrological processes leading to seasonal polar caps of water frost, altering our understanding of the interior of these bodies. Vesta may have rocks more strongly magnetized than on Mars, altering our ideas of how and when dynamos arise with important lessons for Mars, Earth and Mercury. Ceres may have a thin, permanent atmosphere distinguishing it from the other minor planets.

The three principal scientific drivers for the mission are first that it captures the earliest moments in the origin of the solar system enabling us to understand the conditions under which these objects formed. Second, Dawn determines the nature of the building blocks from which the terrestrial planets formed, improving our understanding of this formation. Finally, it contrasts the formation and evolution of two small planets that followed very different evolutionary paths so that we understand what controls that evolution.

This mission is very timely. Its journey in time to understand the conditions at the formation of the solar system provides context for the understanding of the observation of extra solar-planetary systems. It provides data on the role of size and water in planetary evolution and forms a bridge between the exploration of the rocky inner solar system and the icy outer solar system. Finally, it completes the first order exploration of the inner solar system, addresses NASA’s goal of understanding the origin and evolution of the solar system and complements ongoing investigations of Mercury, Earth and Mars.

What impresses me is the lengthy journey – a mission that takes off in September 2007, reaches Vesta in July of 2011, and should reach Ceres in February of 2015. Just hitting the target is amazing – but hitting the target and having the space craft work after all that travel in an extremely hostile environment is really incredible.  Here’s a NASA simulation of the  Dawn trajectory. Click image for larger view.

How does it accomplish this? There is a gravity assist from Mars, but a lot of Vesta’s motion comes from an onboard rocket engine – very unusual. Huge solar panels and the use of a fantastic new type of rocket – the Ion Engine – are the keys. NASA describes it this way:

Ion Engines are the most exciting new rocket propulsion system since the Chinese invented the rocket about a thousand years ago.

Most rocket engines use chemical reactions for power. They combine various gases and liquids to form chemical explosions which push the rocket through space. Chemical rocket engines tend to be powerful but have a short lifetime.

Ion Engines use electric fields instead of chemical reactions. Ion Engines tend to be much less powerful, but they are so efficient, they can last for years before running out of fuel.

To learn more about the Ion Engine, go here.

And I have to admit, I learn best when I can get my hands on something, so while NASA considers model building a “kid’s” activity, I feel it’s a great way to develop a sense of what this mighty little spacecraft is all about. NASA provides directions and plans for a paper model. All you have to do is download, print, cut, and fold. To give it a try, go here.

We started this post by describing how to look out to Vesta. So let’s end it by looking back. It helps put it all in perspective. Here’s a NASA simulation of how the Earth and Sun would look, were you riding on the Dawn spacecraft as it orbits Vesta. (Click image for much larger version.)

Goodbye Saturn, Good Evening Jupiter, Good Morning Mars!

Goodbye Saturn, Good Evening Jupiter, Good Morning Mars! – that about sums up the planets’ parade for this month. Saturn, sadly, is getting lower in the west each evening, and by the end of the month really will be too low for decent views in a small telescope, though you should be able to find it easily enough if you have a clear western horizon.

About an hour after sunset you should see a pair of almost identical "stars" near the western horizon - but only the one on the left (to the south) is a real star. Its name is Spica and it is icy blue in color. The other "star" is Saturn and should look a bit yellowish, though when objects are this close to the horizon colors are tricky. At the beginning of August they will be nearly two fists above the horizon and a little more than one fist apart. By the end of the month they both will be much closer to the horizon. Click on image for larger version. (Prepared from Starry Nights Pro screen shot.)

Jupiter actually rises before midnight at the start of the month and earlier each night as the month progresses – so technically it is now in the evening sky – but again, for small telescope users you’ll have to wait for the early morning hours to get a really good view.

At the start of the month Jupiter is by far the brightest "star" rising in the east and well placed by about 2 am. By the middle of the month it will look like this about 1 am and by the end of the month Jupiter will be close to this location by about midnight. Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

And Mars is definitely an early morning object in the eastern sky and so distant its disc is tiny and really has little appeal for the small telescope user, but for the naked eye viewer it’s fun to watch it zip across Gemini, the Twins.

Mars is playing hard-to-get in August. At the start of the month it's reasonably placed at 4 am in a field that contains several stars brighter than it. It will be about the same brightness as Castor. As the month progresses the stars will rise significantly, but since Mars is traveling eastward quite quickly against the background of stars it takes a step "downward" as the sky background appears to move upward. So while Mars gets higher by the end of the month, it's only by a few degrees. Compare its color to the bright stars Aldebaran and Betelgeuse - all three should have a red tint. Click image for larger view. (Prepare from Starry Nights Pro screen shot.

August events – Get ready for the 2010 Perseid meteors – a special year

Arrows represent Perseid meteors - which can appear anywhere int he sky and will be of different lengths and brightness, but will appear to radiate from a point in the northeast in the constellation Perseus. Click chart for larger version. (Prepared from Starry Nights Pro screen shot.)

For a printer -friendly version of the preceding chart, download this.

The Perseids should be really good this year because the Moon won’t interfere when they are near their peak during the morning hours of August 12th and 13th. Here’s a quick guide.

When:

The night of  August 12-13 starting about 90 minutes after sunset, but best after midnight. And if that night is likely to be cloudy, the preceding night of August 11-12 might prove to be just as good, but the best chance looks like the 12-13.

Where:

Any place you have a clear and dark sky – the more horizon visible the better, but in truth you can only look in one area at a time, so a clear, dark sky to the northeast is best. While a Perseid meteor can appear anywhere in the sky, your best chance to see  several will be to scan the sky to the northeast in the general vicinity of the “W” of Cassiopeia.  However,  you don’t have to fixate on one region. Get comfortable, look high in the northeast, and from time to time look around to different sections of the sky to enjoy the sights and stay alert.

What can you expect to see?

Under the best conditions at the peak of the shower, you can expect to see between one and two meteors a minute! But I never seem to achieve those best conditions, so I don’t raise my hopes too high. I’m just sure I’ll see many more meteors than normal, but fewer than I would in a year when the Perseids are at their very best.  To put numbers to it, I’d be delighted if I averaged one every five minutes. For everyone, everywhere, the intensity of the annual Perseid “meteor shower” is in a downswing, but because we’ll have no interference from the Moon, this should be a better than average year.

Special bonus

Go out early – half an hour after sunset – and bid farewell to the planets we’ve been enjoying as they cluster together to put on a farewell performance in the west.

Mars, Saturn, and Venus are so close they may all nearly fit in the same low power binocular field – and using binoculars will make them much easier to pick out in the twilight, though certainly Venus should be enough to guide you to the others. What’s more, a three-day-old crescent Moon (on  the 12th) will round out this picture. It will be between the planets and the horizon.

Meteors and meteor showers are fun if for no other reason than they are a chance to see something happening in the sky. Much of what we look at doesn’t change – or rather changes so slowly we don’t notice the change. Meteors, on the other hand, demand that you be looking in the right place at the right time. Only on the very rare, very bright meteors do we actually have time to alert others and have them turn their heads and see what we see.  And what we see is a space event happening closer to us than any other natural one. What’s more, meteors can have real scientific value.  They are viewed by some as our cheapest “space probe.” They are relatively pristine bits of matter left over from the early days of the solar system and so can tell a story to those who know how to read them.

Meteors – “falling stars ” – can be seen any time. You don’t have to wait for a “shower” like the Perseids; you just have to be lucky. But they are most frequent at certain times in the year when the Earth happens to be plowing through a meteroid-rich area.  We call this occasion a meteor shower. (For your dictionary: A meteroid is a small bit of space rock that becomes a meteor when it collides with our  atmosphere and heats to incandescence as it descends towards Earth. When it gets here – which is rarely as anything except fine, incinerated dust – it is a meteorite. )

The reason for a shower such as the Perseids is that we are passing through the debris trail of a comet. Think about it. The general model for a comet is a “dirty snowball,” and as that dirty snowball nears the Sun it melts, and as it melts it leaves a trail of dirt particles behind it – particles that remain in orbit until something like the Earth sweeps by and captures some of them with its gravity.

The comet itself can vanish entirely – but the result is a river of space dust – a river that is most intense nearest where the comet actually was.  That’s why there are some years – the 1990s in the case of the Perseids – when the meteor shower is more intense than others.  Now we are in a period when we are passing through the trail of the comet that creates the Perseids at a point where that trail is relatively sparse – so there will simply be fewer Perseids than there were  15-20 years ago..

That trail is not encountered all over the sky. It collides with our atmosphere near a particular point in our sky. That point is called the radiant – you might think of it as a hole through which the Perseids fall – and in the case of the Perseids, it appears to be in the constellation Perseus.  But we don’t see all the meteors at this point. We see a meteor only when its collision with our atmosphere is intense enough to make it burn up. The faint meteors we see are made by a speck of dirt about the diameter of a pencil lead. The brightest ones are caused by something about the diameter of the pencil’s eraser.  In either case it will, for all practical purposes, burn up entirely in our atmosphere – 50 to 75 miles up – and nothing significant will remain for anyone to find on Earth. But exactly where it burns up is another thing. That’s why we will see a sudden flare – a falling star – anywhere in the sky.

And that’s awesome! Think about it a moment. If someone struck a match 50 miles away would you see it?  Yet a grain of sand, hurtling into the atmosphere, shows us such a brilliant light we can’t miss it!

When you are watching for Perseids, you don’t have to look near the radiant point, though you will see more there.  A meteor can flare up suddenly anywhere and appear to draw a short (usually 5-10 degrees long) straight line across the dome of the sky. (Bright ones may actually leave a trail, which you can see for a few seconds with the naked eye or longer with binoculars.) If we trace a line backwards along the meteor’s trail we will see it comes from the area near the radiant point.

In the early evening, that Perseid radiant point is low in the northeast. That means nearly half the meteors that are radiating from it are happening below our eastern horizon. That’s why the shower is best in the early morning hours when the radiant is high in our sky. If the radiant is overhead, then we have nearly doubled our chances of seeing a meteor.

There are many meteor showers in the course of a year and some are better than others. The Perseids is one of the most reliable ones and happens to come at a convenient time for northern hemisphere observers when it is comfortable to be out at night, lying on the ground, and looking up.

Personally, I don’t like the word “shower.” It immediately gives the impression that what we are going to see will be more intense than what most of us actually experience. I prefer calling this a meteor “event.” But, we have been calling such events “showers” for years, and too often they are hyped in the press and then people are disappointed when nothing like a shower occurs. So keep your expectations realistic and you won’t be disappointed.

In the final analysis there’s only so much time you can spend lying on your back gazing at the starry sky; though I very much enjoy that time, it’s made much more enjoyable by knowing that at any instant there’s a heightened likelihood that I will see a bright meteor.  That – and the summer Milky Way – make looking for Perseids in a dark and moonless sky always worth the effort for me.

Close encounters of the planetary kind

Jupiter is the real fun for telescope users this month and starts to provide a great naked eye beacon in the eastern sky. It rises a couple of hours after sunset at the start of the month and by the end of the month will become a dominant, planetary beacon in our evening sky. But for early August evenings, the planet show for naked eye and binoculars is mostly in the west – though those who stay up late to see the Perseid meteors will be treated to a brilliant Jupiter as well.

Saturn, Mars, and Venus – with a bit part by Mercury – play out the last act of their current drama on the western stage shortly after sunset, with the climactic event centered on August 7, but fun to watch both before and after that.  This is the sort of thing you need to see in your mind’s eye, bearing some resemblance to waltzing elephants. Well, maybe that’s an unfair image.  Kepler would have watched and I suspect heard the music of the spheres. And we should too.  But the emphasis for me needs to be on size.

We’re watching dots of light dance in the western sky. But what we are really seeing is the precisely choreographed movements of the planets with that mystery of mysteries – gravity – dictating the action. And we’re part of it, of course. What we see depends upon where we stand and we’re certainly not standing still. So here we are on the third rock from the Sun, spinning at the dizzying speed of roughly 800 miles an hour – at mid-northern latitudes – and tilted  at the crazy angle of 23.5 degrees and rushing around  our central star at 66,000 miles an hour, and from this incredibly hurried platform we can watch night after night as the second rock and the fourth rock appear to  approach one another in our twilight sky, while the more stately frozen gas ball – Saturn, with its magnificent rings – looms nearby. And off to one side, nearly lost in the dying glare of our own star, is the first rock, tiny, whizzing Mercury, scooting out from the Sun, but at such a low angle for us it will be a challenege to see, making binoculars extremely helpful if we wish to track it down – not to mention unusually clear skies.

That’s what’s going on. Here’s what it comes down to in more mundane terms.

On August 1, as we look west 30 minutes after sunset from mid-northern latitudes – about 42-degrees –  the actors are here:

Look for Venus first - that will be easy and your guide to the others. It's about 15 degrees - a fist and a half - above the horizon, so you can judge other distances from that. Of course, as time goes on and the sky gets darker, the planets are easier to see - but they also are getting closer to the horizon making them more difficult to see. Click image for larger version. (Prepared from a Starry Nights Pro screen shot.)

For a printer-friendly version of the preceding chart, download this.

On August 7, 30 minutes after sunset, they should look like this – and that’s about as high as Mercury will get this month:

Venus, Mars, and Saturn should fit easily into the same binocular field of view - they are separated by just under 5 degrees and roughly 15 degrees above the horizon. Mercury will be much more of a challenge, requiring unobstructed horizon and very clear skies. Click image for larger version. (Prepared from Starry Nights Pro screen shot.)

For a printer-friendly version of the preceding chart, download this.

And Venus and Mars hang close, moving at roughly the same speed as seen from our moving platform against the background of stars, until near the end of the month. Then they join the bright blue star, Spica, and this union carries them into the first week of September. This is how they’ll look on August 29th.

The planets are lower now - about one fist above the horizon half an hour after sunset - but Venus still provides a bright guide to finding the others. Venus, Mars and the guide star, Spica, all fit in the same binocular field of view, but Staurn is off by itself, much closer to the horizon and Mercury has headed off towards the morning sky. Click image for larger view.(Prepared from Starry Nights Pro screen shot.)

For a printer-friendly version of the preceding chart, download this.

  • August 1 – Check out Venus, Mars, Saturn and Mercury in the west
  • August 3 – Last quarter Moon
  • August 7 – Mars, Saturn, and Venus closest together
  • August 9 – New Moon
  • August 11 – Try to catch the thin crescent Moon near Mercury very low in the west. If no luck on this night, don’t despair.   The Moon will still add to the twilight planet show for the next few nights.
  • August 11-12 or August 12-13 – These are the nights to look for Perseid meteors. The best opportunity should be after 11pm on the 12th,  but the same start time applies to the 11th. This is really an early morning event.
  • August 16 – First quarter Moon
  • August 24 – Full Moon
  • August  27 – A waning gibbous Moon will rise side by side with Jupiter  about one hour after sunset – Jupiter will be nearly due east, the Moon about one fist north of it.

Look North In August – All hail the Queen! (OK – the “W”)

Click image for larger view. (Derived from Starry Nights Pro screen shot.)

For printer friendly chart, download this.

The easily recognizable “W” of Cassiopeia (kass ee oh pee’ uh), the Queen, is well up in the northeast early on an August evening. Find it and you have a good starting point for tracing the Milky Way on south through Deneb.

When the “W” circles to a point high overhead, it will look like an “M,” of course, but that’s just part of the fun. Some people also see this asterism as forming the chair – or throne – for Cassiopeia. I like it because along with the Big Dipper, it nicely brackets the north celestial pole and provides another rough guide for finding Polaris. As the “W” rises, the Dipper plunges until it may be too close to the horizon for many to see. Both the stars of the Dipper and the stars of the “W” are 28 degrees from Polaris – roughly three fists.  When the Dipper gets on the horizon, the “W”  turns into an “M” directly above Polaris, so just measure three fists down from this “M” and you should be in the right region for finding the North Star.

Normally I do not find constellations or their associated myths too useful. Cassiopeia is an exception. Knowing the myth connected with this constellation will help you remember several important neighbors, and though we’ll meet these in the next two months, I’ll give you a “heads up” now and repeat the story when we meet the others. It goes like this:

Cepheus (King of Ethiopia)  and Cassiopeia (Queen of Ethiopia) have a beautiful daughter, Andromeda. Cassiopeia bragged so much about Andromeda’s beauty, that the sea nymphs got angry and convinced Poseidon to send a sea monster to ravage Ethiopia’s coast. To appease the monster, Cepheus and Cassiopeia  chained the poor child (Andromeda)  to a rock. But don’t worry. Perseus is nearby and comes to the rescue of the beautiful maiden, and they ride off into the sunset on Pegasus, Perseus’ flying horse! These five constellations – Cepheus, Cassiopeia, Andromeda, Perseus, and Pegasus – are all close to one another in the sky and all are visible in the fall, so we will meet them soon.

One of the bright stars of Cassiopeia is also a special aid to finding your way around the heavens, but in a more modern sense. It is part of an asterism known as the “Three Guides.”  These three bright stars are all very close to the Zero Hour Right Ascension circle in the equatorial coordinate system – the system that is roughly the celestial equivalent of latitude and longitude and is commonly used to give a permanent address to stars and other celestial objects. These three bright stars mark a great circle that goes through both celestial poles and the equinoxes and is known by the imminently forgettable name of  “equinoctial colure.”

Click image for larger view. (See note at end of post for source of this drawing.)

We’ll meet the other two stars in this asterism next month, but for now, simply take note of Beta Cassiopeia. It’s marked on our chart and is the bright star at that end of the “W” that is highest in the sky this month. Remember that this star is very near the “0” hour  circle, which you can visualize by drawing an imaginary line from Polaris through Beta Cassiopeia and eventually the south celestial pole. This line will cross the ecliptic at the equinoxes.  Of course, this helps only if you are familiar with the equatorial coordinate system! If that means nothing to you, then don’t clutter your mind with this right now.

The source for the drawing showing the equinoctial colure can be found here.

Look east! In August 2010 – kick back, lie back, look up and enjoy our home galaxy!

This is the month to meet your neighbors – a few billion of them at least!

In August we break our pattern of focusing on bright stars and instead focus on that ancient stream of stars known as the Milky Way – our own galaxy. This means observing a bit later than normal, and if you live within urban or suburban light pollution, going to where you have really dark skies. This does not mean you have to move to – or visit – Arizona. I live in one of the worst light pollution regions of the US, and I can see the Milky Way from my back yard – and see it even better if I take a 12-minute drive to a nearby wildlife sanctuary. But I do have significantly darker skies than people just a mile or two from me. You need a clear moonless night and your eyes need to be well dark adapted. Then you want to look up for a wide, faint “cloud” with a  roughly north-to-south orientation.

I've reduced the brightness and contrast on this image in an attempt to approximate what can be seen from an area with light to moderate light pollution. Still, a photograph always shows more - but it just can't capture the magic of being there. In this case the photographer also caught a Perseid meteor. As you can see, the heart of the Milky Way is nicely framed by the bright Summer Triangle stars of Vega, Deneb, and Altair. Click image for larger version.

Seeing the Milky Way is worth the special effort. It is one of the most beautiful and awe-inspiring astronomical sights, and your naked eye is the best way to take it all in, though binoculars will provide a special treat as well.  In what follows, we’ll focus on where you should be to observe the Milky Way, when you should look. and finally,  where in the sky you should look.

1. Where you should be

Sadly, most people today are routinely denied this sight because of light pollution, but don’t despair! While the darker your skies are, the better, like me you may find that pretty dark skies are just a short drive away. There is an international guide to light pollution and here’s what it shows for light pollution in and around “Driftway Observatory,” my backyard.

On this map of light pollution for southeastern New England, Driftway Observatory is right in the center on the border of an orange/yellow area. Obviously black is the best. Blue is darned good. Green and yellow are desirable. Orange means getting poor; red and white are quite terrible. You should look for at least a yellow area - but to the south of a heavily light-polluted city if possible.

You can get a map  for any region of the world. The simplest path is to go here. Scroll down, to the thumbnail maps and choose a region of the world that suits you and download the map for that region. Another path is limited to observers in the United States, Canada, and Mexico. For them there are “Clear Sky Charts” – astronomical viewing weather forecasts – for hundreds of locations. You can find a location near you by starting here.  Underneath your regional Clear Sky Chart you will see a short list of “Nifty links.” The last one takes you to a light pollution map for that region. It may be helpful to know your latitude and longitude first, so If you don’t know what it is, you can find it here. All of this is useful information for any sky observer to have, so if you track down a Clear Sky Clock for your region,f or example, bookmark it.

Here’s how to make sense of the light pollution maps in terms of seeing the Milky Way.

Red – “Milky Way at best very faint at zenith.”

Orange – “Milky Way washed out at zenith and invisible at horizon.”

Yellow – “Some dark lanes in Milky Way but no bulge into Ophiuchus. Washed out Milky Way visible near horizon.”

Green – “Milky Way shows much dark lane structure with beginnings of faint bulge into Ophiuchus.”

If you can get into the blue, grey, or black areas – enjoy! I envy you 😉

One critical point though: Pay attention to where there are cities. They will create light domes that will wash out at least areas fairly low in the sky. In my situation I have two small cities, Fall River to the northwest and New Bedford to the northeast. Both have populations of around 100,000 and both create light domes in those regions of the sky. Fortunately, the northern sky isn’t important for seeing the Milky Way, especially in August. But if you have a large city – or shopping mall, or anything that might create a light dome – it is better to look for an area south of it. In August in mid-northern latitudes the  Milky  Way is best from right overhead on down to the southern horizon. That’s why my best view is from a wildlife sanctuary just a few miles away and right on the north shore of  Buzzards Bay and the ocean. It means when I’m looking at the southern Milky Way – towards the very center of our galaxy – I’m seeing it over a huge expanse of water where light pollution is the least.

2. When to look

Begin looking early on a moonless, August evening and ideally, when the skies are crystal clear – frequently this comes right after a cold front passes. Although the Milky Way can be seen many months of the year, one of the best times to see it is in August, about two hours after sunset. In 2010 your best views will come between August 1st and 15th – after that the Moon will offer more and more interference each night for the next two weeks.  However, by the 31st, you should get in a solid hour of Milky Way treat before the waning, gibbous Moon rises. If you miss it in the first two weeks of August, try again the first two weeks of September – this guide will still be useful, though everything will have moved higher and to the west a bit.

I say two hours after  sunset because it takes that long in mid-northern latitudes for it to get fully dark at this time of year, and you need full darkness. (You can find out the local time Astronomical Twilight ends – when it is fully dark – by going to this Web site. From the drop-down menu you’ll find there, choose “astronomical twilight.”) However, you can certainly start looking earlier. This is something where beach chairs or lounges are nice, and maybe even a blanket.  You can start about an hour after sunset when the brightest stars are visible. This will help you get your bearings and you can dark adapt as the skies get darker.

Finally, you need to protect your eyes from white lights. It takes 10-15 minutes for your eyes to become about 50 percent dark adapted. At that point your color vision is as good as it will get, but your sensitivity to dim light will continue to increase. In another 15 minutes or so you will reach about 90 percent dark adaption. The remaining 10 percent can take as long as four hours.  So I consider that after half an hour my eyes are about as good as I can expect them to be.  During all this time and beyond you should avoid looking at white light. You can use a red light to check a chart if you like, but keep it dim and use it sparingly. If you’re in a location where automobiles drive by, don’t look at them – close your eyes and turn away.

Where to look

When you set up your blanket or lounge chair, do your best to align it on a north-south axis with your head to the north and feet to the south. You may want to favor the east just a bit.

What you want to find as you start out is the familiar guidepost stars of the Summer TriangleVega, Deneb, and Altair. These were new guidepost stars in May, June, and July. If you are just starting this journey in August,they are still easy to pick out from our chart.  As the sky in the east starts to darken they will be the first stars visible, 30-45 minutes after sunset.

Click image for a larger view. (Derived from a Starry Nights Pro screen shot.)

You can download a printer friendly version of this chart here.

The brightest – and highest – of the three will be Vega, which will be approaching a point overhead. There are roughly two fists (24 degrees) between Vega and Deneb and nearly four fists (39 degrees) between  Deneb and Altair, so the Triangle is huge.

These three Summer Triangle stars roughly bracket the Milky Way – that is Vega is near the western border, Altair the eastern border, and Deneb is about at midstream.  But you need to wait, of course, for it to get darker before you can see the Milky Way.   The boundaries of the Milky Way, as with any stream, are not sharp and regular. It tends to meander a bit with little pools of light and some deep, dark areas as well.

As the skies darken and your eyes continue to dark adapt, you should try to find three distinctive asterisms that will anchor both ends of the Milky Way, plus the middle.  If you have found Deneb, then you have the first star in the Northern Cross. In fact, you may want to see this as a stick figure of the constellation Cygnus the Swan.  In that case, Deneb marks its tail; the bar of the cross, its wings, and its long neck stretch out to the south as if it were flying down the Milky Way. To the north you should locate the “W” of Cassiopeia described in detail in our “Look North” post this month. And to the south, find the “Teapot,” which we described in more detail last month. Here’s a chart showing the whole sweep of that section of sky.

Click image for larger view. (derived from Starry Nights Pro screens hot.)

You can download a printer friendly version of this chart here.

Now, if it is about two hours after sunset and if you are in a location away from light pollution and, of course, are enjoying one of those crystal clear nights with dark-adapted eyes, then you also should be seeing the Milky Way. It only takes time and patience for you to trace it out – to see areas that are brighter than others – as well as some dark patches that don’t mean the absence of stars, but the presence of obscuring dust. But don’t think of the dust as getting in the way – think of it as star stuff – for what you are seeing in many sections of the Milky Way are the parts of our galaxy where new stars are being born. Relax and explore with your binoculars – start to absorb the majesty of millions – no billions – of stars!  If conditions are right – and you have a dark sky – it will look to the naked eye like faint clouds that get brighter as your eye traces them out from north to south.

And what is it you are seeing and why does it appear this way to you? That’s the important question. And this is where you have to do some mental gymnastics.

Think of our galaxy as a large pizza pie with extra cheese and goodies heaped in the center.  Now put yourself away from that center – perhaps one-half of the way towards one edge and buried down at the level of the crust. That’s a pretty good simulation of our galaxy and our place in it. You really need to get outside it – we can only do this in our imaginations – and look at it from that perspective. If we could get outside it, here’s approximately what we would see:

Two view of our Galacy, the Milky Way. The one on the left is from  aposition above it, the one on the right shopws you the galaxy edge-on.  This is a screen shot from the wonderful, free software, "Where is  M13."

The image on the left is how we think our galaxy would look if we could get above it and look down on it – like a big pinwheel of stars.  And what if you could see it edge on? Well, that’s the picture on the right. (This is a screen shot  from a wonderful – and free – software program called “Where is M13” that helps you understand where various objects really are in relation to us and the rest of the galaxy.)

OK – focus on the edge-on image – and note how really thin most of the galaxy is. It is about 100,000 light years across, but on average just 1,000 light years thick.

plane_view_MW

Now imagine yourself on a small dot (the Earth) rotating around that small dot in our image – the Sun. Do you see a lot of stars when you look “up” – that is, look in the direction of the words  “The Sun.”

No – in fact, if you look down, you don’t see many stars either – or for that matter, if you look in just about any direction there are relatively few stars visible to you. Why? Because the disc is just 1,000 light years thick, and most of the time you’re looking right through it the short way.  But  look along the plane of the galaxy – say  directly to the right or left – and what a difference!

Looking to the left you see many stars – in fact, a thin river of stars. Looking this direction, you’re looking through about 20,000 light years of star-filled space. We are looking along the plane, generally towards the outer rim, when we look at the W of Cassiopeia. Look along the plane to the right, and you see even more stars in a much wider river. Now you’re looking through about 30,000 light years of star-filled space and then right at the star-rich, galaxy core. And this, in a general way, is what we are doing when we look toward the Teapot of Sagittarius. That’s why the Milky Way is so much brighter and denser in that direction.

Not too difficult to understand – but this is only a rough sketch. As recently as 2008 scientists came up with a much different perspective of our galaxy than we had had up until then. Prior to the latest study, we thought the galaxy was a spiral with a bulge in the center and four main arms. Now they see it as a barred spiral – that is, the bulge in the center looks more like a bar that spills into two – not four – main spiral arms. There are other smaller arms in the spiral, and it all gets quite complex.

The problem, of course, is there is no way we can get outside our galaxy and look in. The distances are incredibly vast. Even if we could send a space probe at the speed of light, it would be thousands of years before it got outside our galaxy, took some pictures of us, and sent those pictures back. So we have to try to decide what the galaxy really looks like from the outside by studying it from the inside. Imagine, for a moment, being inside your body and trying to figure out what you look  like by what you can see from the inside, and you get an idea of the problem. Fortunately we can see other galaxies, and in later months we’ll be looking at one that looks a lot like what we think ours would look like if we could only get outside it and look back.

Meanwhile, relax – look up – and dream of all  the wonders that are out there and sending their messages back to you in the form of millions of tireless photons that have traveled thousands of years to reach your eyes and ping your brain on this dreamy August evening.  Harvest some of those photons by surfing the Milky Way with your binoculars. You will notice that in some areas it is quite dense and you may even discover some tiny, tight clusters of new stars – or a globular cluster of old stars, or even a little hazy patch where new stars are being born.  You need a telescope to see these well, but you can just discern some of them with binoculars, and with telescope or binoculars, what you really need to see with is your mind’s eye. Knowing what you are looking at is what brings this faint cloud alive and turns it into the awesome collection of billions of stars – and more billions of planets –  that it is.

2009 Perseid meteors put on great display – better than expected!

Of course you needed clear skies and here in Westport, Ma. the two nights brought only one brief window of opportunity and a handful of meteors in bright moonlight. But even a predicted – and unusual – spike in Perseid activity came through on schedule.

Sky and Telescope gives this example as a typical experience:

The wife, daughter and I set up camp in the back of the pickup here in Livermore [California] last night for a star show my 11 year old daughter will never forget,” writes a commenter named Deadzheadz. “From 9:30 until 11 p.m. we spotted 25 to 30 meteors coming down. Some were so long and bright we had to turn our heads to follow the complete tail.

You can read the full Sky and Telescope report here.

My report of a brief, lucky break in the clouds is here.

Mars will NOT be close to Earth, nor “as large as the Moon” in August 2009 or ever!

Sorry I have to write this, but every August since 2003 I have gotten these questions about a spectacular showing of Mars in our sky because an anonymous email makes the rounds of the Internet causing people to get excited. THIS EMAIL IS NOT TRUE. Two people have asked me about this in the past couple of days and I suspect there are a lot more innocent folks who are looking forward to something that just isn’t going to happen – this year, or ever.

The most outrageous claim in this email goes something like this:

On the night of Aug. 27, the planet Mars will come closer to Earth than it has in the past 60,000 years, thereby offering spectacular views of the Red Planet.  Mars will appear to the naked eye as bright as and as large as the full moon. No one living today will ever see this again!

No one living today will ever see this. Period. OK. here’s the simple truth. Mars is in the morning sky this August, near the bright, red star Aldebaroan. (See my post on observing August planets here.) To the naked eye both will look like stars of roughly the same brightness and hue. In a very good telescope, Mars will look like a very tiny planet, about one-fifth the size it is when it actually does make a close approach to Earth.  Mars and the Earth are relatively  close to one another  – 35 to 50 million miles apart – every two years. I saw it August 7, 2009.  Fun, but far too small even in my best telescope, to see any details on it.

How does this compare with the Moon for size?  The moon is roughly 30 minutes of arc – half a degree – in our sky. Mars is rougly 5 seconds of arc. That means that this August the Moon is about 360 times as large as Mars in our sky. Or think of it this way – if the Moon looked  as big as a football field, Mars would look about the size of a football. Even when Mars is seen at its largest, as it was in 2003, the Moon was still 72 times as large!

In short, this Mars email is just another Internet urban legend telling us things that would be fun if they were true, but really are far, far from the truth. For details on this, please visit the Snopes.com site – in fact, anytime you receive an email that sounds too good to be true – on almost any subject – check snopes.com before you forward the email to friends. It’s a great clearing house forgetting ut the truth on these legends.

Be the first on your block to build your very own Milky Way Galaxy!

Editors note: This is a companion project to the post on viewing the summer Milky Way found here.

OK – the universe beat you to it by roughly 13 billion years. But you can build a scale model of the Milky Way, and in doing so you’ll develop a better feel for its size, its relationship to other galaxies, and why the Milky Way looks like the Milky Way when you see it in your sky. Essentially, all this project entails is printing the image below and gluing it to a disc that is the appropriate thickness. How thick is that? About 2 mm – a little more than one-eighth of an inch. I glued it to cork, but cardboard of similar thickness would be fine.  Two millimeters will seem mighty thin – but it is believed that our galaxy – at least in the spiral arms where our Sun is located, is actually just 1,000 light years thick.  Since it is believed to be 100,000 light years across, that means the thickness is 1/100th the diameter.  If your printed version of thegalaxy image is dramatically different in size  – say 150 mm (6-inches) in diameter rather than 200 mm (8-inches), then simply reduce the thickness of your backing to 1.5mm or about 1/th of an inch. The exact size will depend on what image you print from and how your computer handles the printing. But don’t get all fanatical about these dimensions. They are much more than guesses, but something less than precise. After all, no one has ever been outside our galaxy to look in at it, and it would take millions of years to send a space probe out of the galaxy, take a picture, and send it back.

CLick on this image to get a scale image suitable for printing. This is the basis for your scale model of the Milky Way. When printed it should be approximately 200 mm in diameter. The scale is 10 mm equals 50,000 light years.  This is created from an artist's conception published by NASA. All the instructional images are clickable as well, so if you need a larger image, just click it.

Click on this image to get a scale image suitable for printing. When you get to that image you might want to simply print the web page, or you could right click - or control click - to save the image to your computer, then open it in the appropriate software and print. This image is the basis for your scale model of the Milky Way, so you need to print it one way or the other. When printed it should be approximately 200 mm in diameter. The scale is roughly 100 mm equals 50,000 light years. This is created from an artist's conception published by NASA. I added the green dot - showing the approximate location of our Sun - as well as the tabs which will be explained in the text. All the instructional images that follow are clickable as well, so if you need a larger image, just click it.

Click image to get alarger version of this text for printing. This text will be printed,t hen pasted on the back of your scale model.

This text - to be pasted on the back of your model - is really an image. Click the image to get a larger version of this text for printing.

Step-by-step

Materials: I used cork board that was little more than 2mm thick and about 200 mm x 250 mm (3/32 x 8 x 10 inches). I used both white glue and rubber cement and scisors for paper,  as well as stronger sheers to cut the cork. The only other materials are the two print outs shown above and a small piece of your backing material - can be cut from scrap - to use to make the galaxy core appear thicker.

Materials: I used cork board that was little more than 2 mm thick and about 200 mm x 250 mm (3/32 x 8 x 10 inches). I used both white glue and rubber cement; scissors for paper, as well as stronger shears to cut the cork. The only other materials are the two print outs shown above and a small piece of your backing material - can be cut from scrap - to use to make the galaxy core appear thicker.

Step 1

Step 1: Cut out the image of the galaxy, being careful to leave the tabs in place. These tabs tie to asterism mentioned in the observing the Milky Way article found here - as well as take note of the positions of "0" and "180" degrees of galactic longitude. We'll explain how to use them once the model is finished.

Step 1: Cut out the image of the galaxy, being careful to leave the tabs in place. These tabs help you locate asterisms mentioned in the observing the Milky Way article found here - as well as take note of the positions of "0" and "180" degrees of galactic longitude. We'll explain how to use them once the model is finished.

Step 2

Cut out a small piece of your backing material about the size and shape of the tellow galactic core. Position the image on your backing and slide this core piece into position underneath it. Trace around the core with pen orpncil to indicate where it will be glued.

Step 2: Cut out a small piece of your backing material about the size and shape of the yellow galactic core. Position the image on your backing and slide this core piece into position underneath it. Trace around the core with pen or pencil to indicate where it will be glued.

Step 3

Step 3: Glue the "core" layer onto your backing sheet. With the cork I had to put a coating of white glue on, let it dry a little, then add a second coating.

Step 3: Glue the "core" layer onto your backing sheet. With the cork I had to put a coating of white glue on, let it dry a little, then add a second coating.

Step 4

Step 4: While you;re waiting for the core backing to dry, cut out the text that will go on the back. This is a tight fit, so trim close to the words.

Step 4: While you're waiting for the core backing to dry, cut out the text that will go on the back. This is a tight fit, so trim close to the words.

Step 5

Step 5: Avoiding the tabs, but glue (I used rubber cement) on the back of the galaxy image.

Step 5: Avoiding the tabs, put glue (I used rubber cement) on the back of the galaxy image.

Step 6

As you glue the image to the base, bend the tabs up out of the way - and, of course, be sure to position this so the yellow galaxy core is over the raised area - aside fromthat there is nothing crucial about the positioning.

Step 6: As you glue the image to the base, bend the tabs up out of the way - and, of course, be sure to position this so the yellow galaxy core is over the raised area - aside from that there is nothing crucial about the positioning.

Step 7

Carefully cut the base around the image. Be sure not to cut the tabs which should be bent up, out of the way.

Step 7: Carefully cut out the base around the image. Be sure not to cut the tabs, which should be bent up, out of the way.

Step 8

Flip you model over and bend each of the tabs down and glue themt o the back side. I was able to do this with ruber cement, though I suspect white glue might work better.

Step: 8: Flip your model over and bend each of the tabs down and glue them to the back side. I was able to do this with rubber cement, though I suspect white glue might work better.

Final Step

Final step: Glue the text in place on the back.

Final step: Glue the text in place on the back.

The finished scale model of our Milky Way Galaxy . . .

mw_finished

. . . and how to use it.

First, the green dot not only marks the approximate location of our Sun and solar system, but it also covers the approximate area where you will find just about all of the naked eye stars that you see. That alone should give you pause for thought.

But the main point of this model is to drive home the basic shape of the galaxy – not unlike a pizza pie – and to help you see why the Milky Way makes a thin cloud of stars across our sky. Imagine yourself at the area of the green dot. Now imagine you’re in the middle of it – that is, down one millimeter from the surface, or about 500 light years by this scale. Now if you look up, you are looking through a thickness of 1 mm – 500 light years of stars. And if you look down, the same thing. In fact, just about any direction you look, you don’t see many stars before you get to the surface – the outer reaches  – of our galaxy.

BUT . . . if you look along the plane of the galaxy toward the core, you are now looking through about 75,000 light years of stars – so you see many more – but they are very distant and also very faint. They make a faint, hazy cloud across our sky – a thin line. a river – what we call the Milky Way.  And if you look outward along the plane in the opposite direction, then you are looking through perhaps 25,000 light years of stars, so you also see a Milky Way – but I think of this one – the winter Milky Way – as skim milk, for it’s much thinner 😉

And this is where the tabs come in. One says “Teapot.” When you look from the green dot toward the “Teapot”  tab, you are looking through the core of our galaxy – and this what you are doing when you look at the Teapot asterism in our summer sky. Similar tabs mark the “Cross” and the “W” asterisms and show you the direction you are looking when you see those in your sky.  (If these asterisms are not familiar to you, be sure to read the post on looking at the Milky Way in August. )

In the winter time we also see the Milky Way, but it is not as bright. That’s because you are looking outward in the general direction of the constellation “Orion,” which is the other tab.

Whatever time of year it is, try this. Bring your scale model of the Milky Way outside under the stars with you. Find the Milky Way overhead. Then hold your model up and orient it so the edge of your model aligns with the Milky Way. That should give you a sense of the plane of the galaxy and where we all are in this vast river of stars.

What about M13 and many other objects you look at with binoculars and telescope? You can find many of them if you understand the galactic coordinate system explained below. But even if you don’t understand this system, there’s a wonderful – and free – computer program that works on any computer that will help. It’s called “Where is M13?” It will show you exactly where you are looking relative to our galaxy when you look at any of the Messier objects.  It’s easy to download and install. Just go here.

How about the next nearest galaxy? Well, there are several very small galaxies that are very near, but usually what we think of as the next nearest galaxy is one that’s close to being our twin – the Great Andromeda Galaxy, M31.  What’s most interesting to me is to consider these two questions in tandem: How far is it to the nearest star after our Sun? And how far is it to the Andromeda Galaxy? If we reduce our Sun to an eight-inch ball – about the diameter of our galaxy model – then the next nearest star  – the next nearest eight-inch ball – is roughly the distance between Boston and Hawaii – essentially half an earth away! That’s a whole lot of empty space betwen stars. So where is the next large galaxy? Well, the Andromeda Galaxy is about 2.5 million light years away. That would be about 200 inches away on the scale of our model – a bit less than 17 feet! That’s mighty close – and, by the way, getting closer. In fact, scientists feel we’re heading for a collision with the Andromeda Galaxy – but don’t lose any sleep over it – it won’t happen for about 3  billion years! (But you can see a simulation of it right here and now!)

Galactic coordinate system

Editor’s note: The best explanation of the galactic coordinate system I have found is in the brief manual for “Where is M13.” Its author, Bill Tschumy, graciously gave permission to reproduce it here with its accompanying diagram.

The galactic coordinate system is the key to understanding where objects are located within the Galaxy. It was established in 1958 by the International Astronomical Union and is useful for specifying an object’s location relative to the Sun and the galactic core of the Milky Way.

The galactic coordinate system is a 2-D spherical coordinate system with us (or the Sun) at its center.  It has latitude and longitude lines, similar to Earth’s. In fact, a good analogy is to imagine yourself standing at the center of a hollow Earth looking at the latitude and longitude lines on the Earth’s surface. The galactic coordinate system is similar except we are looking out at the celestial sphere.

There is a one-to-one mapping between the galactic coordinate system and the more familiar equatorial coordinate system. Relatively simple equations can be used to convert from one to the other.

galactic_coordinates

The galactic equator (i.e., 0º galactic latitude) is coincident with the plane of the Milky Way Galaxy and is shown as the red circle in the image above.  Galactic latitude is the angle above or below this plane (e.g. the yellow angle above).  Thus, objects with a galactic latitude near 0º will be located within the Milky Way’s spiral arms. Objects with a positive galactic latitude will be above the arms in the northern galactic hemisphere.

Galactic longitude is measured from 0º to 360º, counter clockwise as seen from the north galactic pole. 0º galactic longitude is arbitrarily defined as the direction pointing to our galactic center.  Within the plane of our galaxy (0º galactic latitude), the main points of longitude and the Milky Way constellations which lie in their directions are as follows:

  • 0º is in the direction of Sagittarius
  • 90º is in the direction of Cygnus
  • 180º is in the direction of the galactic anti-center in Auriga
  • 270º is in the direction of Vela

Now consider an object and its galactic coordinates. Any other object lying along the same line of sight will have the same coordinates but only differ in its distance component. An object’s distance is not part of its galactic coordinates. However, knowledge of an object’s galactic latitude, longitude and distance, does allow us to uniquely locate it within the 3-D space around the Milky Way.  Where is M13? uses this information to plot deep sky objects in its Galaxy View.

Get ready for the 2009 Perseid meteors – but don’t expect a shower!

When:
The nights of August 11-12 and August 12-13 starting an hour after sunset.

Where:
Anyplace you have a clear and dark sky – with as much horizon visible as possible.

Look:
Northeast – while a Perseid meteor can appear anywhere in the sky, your best chance to see  several will be to scan the sky to the northeast in the general vicinity of the W of the Cassiopeia.  However,  you don’t have to fixate on one region. Get comfortable, look high in the northeast, and from time to time look around to different sections of the sky to enjoy the sights and stay alert.

The W of Cassiopeia, rising in the northeast after sunset, is a good place to start looking for Perseids. The actual radiant point is below it in the constellation of Perseus. Click for a larger image. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

The W of Cassiopeia, rising in the northeast after sunset, is a good place to start looking for Perseids. The actual radiant point is below it in the constellation of Perseus. Click for a larger image. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

What can you expect to see?
More meteors than normal, but far fewer than you would in a year when the Perseids are at their best.  I will be happy if I see one every five to 10 minutes. For everyone everywhere, the intensity of the annual Perseid “meteor shower” is in a downswing and will be further reduced this year by competition from a bright moon. In North America the predicted shower peak comes at mid-day when, of course, none will be seen because it’s – well, day! That’s why it’s recommended to look either the night before or the night after the predicted peak of 18 hours Universal Time August 12.

The moon is especially bothersome because it will be near last quarter – bright enough to drown out many meteors – and will rise around midnight.  The shower is normally best seen after midnight because it is then that its radiant point is highest in the sky. So when the most meteors would normally be seen, there will be the most interference from the moon.

So, should you just not bother with the Perseids this year? No.  I certainly intend to take advantage of it. If the sky is clear on either night I intend to make them part of the reason to observe, but not the only reason. I won’t lie in a beach chair looking up most of the night as I have done other years.  Instead, if the skies are clear, I plan to head for the darkest spot nearby – Allens Pond Bird Sanctuary – and from there I will do three things:

  • Enjoy the summer Milky Way and the Perseids for the hour or two before the moon comes up and the skies are genuinely dark. During that time I will lie back in a rotating beach chair, binoculars at the ready, and look for Perseids.
  • After the moon rises I intend to enjoy a night full of planets and double stars, as well as the moon.
  • And as the icing on the cake, I’ll continue to keep my eye out for more meteors than I can expect to see on a typical night.

So what’s a meteor and do they really shower?
Meteors and meteor showers are fun if for no other reason than they are a chance to see something happening in the sky. Most of what we look at doesn’t change – or rather changes so slowly we don’t notice the change. Meteors, on the other hand, demand that you be looking in the right place at the right time. Only on the very rare, very bright meteors do we actually have time to warn others and have them turn their heads and see what we see.  But what we see is a space event happening closer to us than any other.

Meteors – “falling stars ” – can be seen any time. You don’t have to wait for a shower like the Perseids; you just have to be lucky. But they are most frequent at certain times in the year when the Earth happens to be plowing through a meteroid-rich area.  We call this occasion a meteor shower. (For your dictionary: A meteroid is a small bit of space rock that becomes a meteor when it collides with our  atmosphere and heats to incandescence as it descends towards Earth. When it gets here – which is rarely as anything except fine, incinerated dust – it is a meteorite. )

The reason for a shower such as the Perseids is that we are passing through the debris trail of a comet. Think about it. The general model for a comet is a “dirty snowball,” and as that dirty snowball nears the Sun it melts, and as it melts it leaves a trail of dirt particles behind it – particles that remain in orbit until something like the Earth sweeps by and captures some of them with its gravity.

The comet itself can vanish entirely – but the result is a river of space dust – a river that is most intense nearest where the comet actually was.  That’s why there are some years – the 1990s in the case of the Perseids – when the meteor shower is more intense than others.  Now we are in a period when we are passing through the trail of the comet that creates the Perseids at a point where that trail is sparse – so there will simply be fewer Perseids.

That trail is not encountered all over the sky. It collides with our atmosphere near a particular point in our sky. That point is called the radiant – you might think of it as a hole through which the Perseids fall – and in the case of the Perseids it appears to be in the constellation Perseus.  But we don’t see all the meteors at this point. We see a meteor only when its collision with our atmosphere is intense enough to make it burn up. The faint meteors we see are made by a speck of dirt about the diameter of a pencil lead. The brightest ones are caused by something about the diameter of the pencil’s eraser.  In either case it will, for all practical purposes, burn up entirely in our atmosphere – 50 -to-75 miles up – and nothing significant will remain for anyone to find on Earth. But exactly where it burns up is another thing. That’s why we will see a sudden flare – a falling star – anywhere in the sky.

And that’s awesome! Think about it a moment. If someone struck a match 50 miles away would you see it? Evena big, wooden kitchen match? How about amile away?  Yet a grain of sand, hurtling into the atmosphere, shows us such a brilliant light we can’t miss it!

When you are watching for Perseids you don’t have to look near the radiant point, though you will see more there.  A meteor can flare up suddenly anywhere and appear to draw a short (usually 5-10 degrees long) straight line across the dome of the sky. (Bright ones may actually leave a trail, which you can see for a few seconds with the naked eye or binoculars.) If we trace a line backwards along the meteor’s trail we will see it comes from the area near the radiant point.

In the early evening that Perseid radiant point is low in the northeast. That means nearly half the meteors that are radiating from it are happening below our eastern horizon. That’s why the shower is best in the early morning hours when the radiant is high in our sky. If the radiant is overhead, then we have nearly doubled our chances of seeing  a meteor.

There are many meteor showers in the course of a year and some are better than others. The Perseids is one of the most reliable ones and happens to come at a convenient time for northern hemisphere observers when it is comfortable to be out at night, lying on the ground, and looking up.

Personally, I don’t like the word “shower.” It immediately gives the impression that what we are going to see will be more intense than what most of us actually experience. I prefer calling this a meteor “event.” But, we have been calling such events “showers” for years and too often they are hyped in the press and then people are disappointed when nothing like a shower occurs.

In the final analysis there’s only so much time you can spend lying on your back gazing at the starry sky: though I very much enjoy that time it’s made much more enjoyable by knowing that at any instant there’s a heightened likelihood that you will see a bright meteor.  That – and the summer Milky Way – make looking for Perseids in a dark and moonless sky always worth the effort for me.

August 2009 – and all the planets have shown up for the party!

That’s the good news – the bad news is the “party” is an all-nighter. That is, if you really want too see all the planets – and maybe little, demoted Pluto as well – you need to start at dusk and stay at your task well into the wee hours of morning.  For Pluto, you will also need a powerful telescope and better charts than I’ll provide here, but the others can all be seen with the naked eye or binoculars.

But what I like about this situation is it makes it easy – even for those of us using nothing but the naked eye, which is really the focus of this web site  – to  see most planets on a single night and to get a sense of how their position in the sky relates to our position in the solar system and where we all are on our annual journey around  the Sun.

Astronomy is always about two realities – the reality we see and the reality we know. The trick is learning to merge these two so that when you see something in the night sky, you are familiar enough with what is really going on that what you see makes perfect sense, given what you know.

orrery_080109

The best example of this is provided by the two major planets this month – Jupiter and Saturn. The chart above shows the reality we know. It shows where all the planets are at the start of August if you could get  above the plane of the solar system and look down at them. Study it. This is from the online orrery at “Solar System Live.” (http://www.fourmilab.ch/solar/)  I drew the bar across it to represents our horizon – the line between night and day –  and the arrows show the direction the bar is moving as night progresses. To the left this shows how, from our perspective, things are setting in the west – and to the right, how they are rising in the east.

Notice that in this view Saturn is near our western horizon and Jupiter near the eastern horizon. That’s the situation right around sunset. But the sky is too bright then for us to see even bright planets. We have to wait about 45 minutes. At that point, Saturn will look like a first magnitude star about 12 degrees above the horizon almost due west – azimuth 266 degrees – in the early part of the month.

Switch to the east and Jupiter is not so shy. It is at magnitude -2.8 (nothing gets brighter than this except Venus, the Moon, and the Sun), but it is still hugging the horizon. Chances are it is too close for you to see. Give it another 45 minutes – 90 minutes after sunset – and it will be about nine degrees above the horizon a bit south of east. For my latitude – 42 degrees north – it will be at azimuth 118. But the exact position isn’t too critical, since it is so bright and there’s nothing in that general vicinity at this time that will compete with it.

This will change slowly as the month goes on – that is, Saturn gets closer to the horizon at sunset each night and Jupiter rises earlier, until on August 14th Jupiter is rising in the east as the Sun is setting in the west.

Did you notice on the solar system view that Mercury is right over there near the western horizon as well? It is, but this happens to be a fairly poor showing for what is always an elusive planet to catch. Sky and Telescope gives this instruction: “Observers near 40° north can look for it 5° above the western horizon a half hour after sunset from August 6 to August 18th.” Yep – and it will be near magnitude “0” – but you will need a very clear western horizon to see it, and I suggest you search for it with binoculars.  Earlier in the month is better than later for both Saturn and Mercury. As the month goes on Saturn not only gets  closer to the horizon, but also closer to Mercury – and this will make  both very difficult to see. By August 17 the two planets are just 3 degrees apart, but then Mercury is only 2 degrees above the horizon and Saturn about 6.

Much easier to find are our two morning planets, Venus and Mars. Both can be spotted, without strain, with the naked eye. But Venus is by far the easiest. It is a brilliant  magnitude -4 – brighter even than Jupiter, which by this time is well over in the southwest, and should be easy to see low in the east northeast by 3:30 am. By the end of the month you’ll have to wait until about 4:30 am for it to be easily seen – but that’s still two and half hours ahead of sunrise.

Mars is a bit more of a problem, though it rises well ahead of Venus. At 3 am August 1 it is a first magnitude “star” about 7 degrees to the north of Aldebaran, also first magnitude,  and both are roughly 15 degrees above the horizon, a bit north of east. Because Aldebaran is a very red star, it will be interesting to compare it with the “red” planet, but it’s best to wait another hour to do this so both are higher in the sky and not as affected by the atmosphere, which tends to make every bright object colorful.

By the end of the month Mars is higher at 3 am, but Aldebaran is higher still. Mars will form an interesting triangle, though, with Aldebaran and another very red star, Betelgeuse. In fact, if you are up at that hour you get a preview of the early winter sky with the bright constellations of Auriga, Taurus, Gemni, and Orion coming into view, and Mars in the middle of them as our chart shows.

Mars early in th emorning at the end of themonth. Click for larger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Mars early in th emorning at the end of themonth. Click for larger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Returning to the evening sky, this remains a good year to track down Neptune and Uranus with binoculars. Both are relatively easy to find, but offer special challenges.

Notice on the solar system chart how Neptune is roughly in line with Jupiter as we view both from Earth. On August first a careful study of the Jupiter region with binoculars around 10 pm will reveal Neptune at about magnitude 8 and only two degrees to the north (left) – but finding it can be tricky.  Try putting Jupiter in the right-hand edge of your field – or even move your binoculars so Jupiter just drops out of the right hand edge. That way the glare from it won’t interfere with your view.  At that point Neptune should be pretty close to the center of your field of view. There are several stars nearby and both Neptune and Jupiter are changing position as the month goes on. Here’s a chart for August 1.

Neptune and Jupiter at the first of August, 2009. (Clickfor larger view.) (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Neptune and Jupiter at the first of August, 2009. (Clickfor larger view.) (This chart uses a screen shot from Starry Nights software which I have then annotated.)

By the middle of the month, they have drifted a bit farther apart, and there’s a row of sixth magnitude stars in a gentle arc between them. If you compare the first chart and this second one you will see these stars and how the position of the planets change relative to them.

Neptune and Jupiter near the middle of August, 2009. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Neptune and Jupiter near the middle of August, 2009. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

By the end of the month these same stars are closer to Neptune and the gap between Neptune and Jupiter is almost five degrees. That means they both probably fit in the same binocular field, but just barely.

If you look at the horizon line on our solar system chart – especially the eastern one – and note the direction it is moving, then you can see how our view will change during the night. As Jupiter and Neptune get higher we eventually get to a point where Uranus comes into view, then, well after midnight, Mars and Venus put in an appearance.

Uranus is easier to see than Neptune because it’s significantly brighter – about magnitude 6.  We also get a special break this month, for Uranus will form a wide “double star” with 20 Piscium, a star that is just a tad brighter than the planet. But this makes it easy to identify.  Here’s my way to locate it. First, trace out a few asterism in the sky south of east. (The following chart is for 11 pm EDT, August 1, at 40° North – but should serve as a general guide for almost any location.)

This charts helps you locate thegeneral area inw hich to find Uranus. Click forlarger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

This charts helps you locate thegeneral area inw hich to find Uranus. Click forlarger version. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Next, you want to zero in on the Circlet of Pisces and an unnamed trapezoid below it.

Tracking down Uranus with binoculars. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Tracking down Uranus with binoculars. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

The Circlet will not fit quite in the typical binocular field of view. The trapezoid should fit and maybe Uranus at the same time – but the way I find Uranus is to find the trapezoid in my binoculars, then move up so that only its top two stars are visible in the bottom of my field of view. Now up and to the right are two almost identical stars – the higher one is Uranus. It is about half a degree above 20 Piscium, a star that is just a tad brighter, though you will be challenged to tell the difference.  (The charts show only those stars you can expect to see with your binoculars – but depending on the binoculars and conditions, you may not see all of these stars.) Uranus is on the brighter side of magnitude 6 and at this point, at least 10 degrees above the horizon. Waiting until later in the night – or later in the month, this will only get easier as Uranus will get higher.  But as the month goes on it will pull away a little from 20 Piscium. By August 30 they are a degree apart and instead of Uranus being directly above 20 Piscium, it will have moved above and to the right – westward.

And Pluto? I wouldn’t try to hunt it down even with my 15-inch telescope.  Although it is relatively high in the south once it gets really dark, it is much too faint to see in anything except large amateur scopes. And to make matters worse, it has lots of competition, for it is above the Teapot in the middle of the Milky Way, and at magnitude 14, just a faint, faint dot among many, many other faint dots. Better to spend your time exploring the Milky Way itself. See: August Guideposts: Asterisms guide you along the Milky Way.

This is the general area within which you can find Pluto this month. But theplanet is faint and buried with the faint stars of the Milky Way.  (This chart uses a screen shot from Starry Nights software.)

This is the general area within which you can find Pluto this month. But theplanet is faint and buried with the faint stars of the Milky Way. (This chart uses a screen shot from Starry Nights software.)

August Guideposts: Asterisms guide you along the Milky Way

Editor’s note: There’s a companion project to this post  – build a scale model of the Milky Way – here.

One of the most beautiful and awe-inspiring astronomical sights is the Milky Way. Sadly, most people today are denied this sight because of light pollution, but don’t despair! With a little knowledge and just about any pair of binoculars, you should be able to easily spot our galaxy – the Milky Way –  and yes, even travel (with your eyes and binoculars)  toward its core.

We’re going to use our guidepost stars and three easily recognizable asterisms to do just that. Of course, if you can get out, away from light pollution, do so.  I live in one of the most light-polluted parts of the world, the northern half of the Eastern Seaboard of the United States, yet I have just enough rural countryside and ocean nearby to allow me to  regularly enjoy the Milky Way from my backyard, and I see it even better if I take a 15-minute drive to a site nearer the ocean. So this guide is for those at dark sites using just the naked eye, as well as for those who live in more light-polluted suburbs.

Here’s when and where and how to look.

When? Early on a moonless, August evening when the skies are crystal clear – frequently this comes right after a cold front passes. Although  the Milky Way can be seen many months of the year,  one of the best times is in August, about two hours after sunset.

Where? I would say anywhere except the city – and if there is a city nearby, try to orient yourself so it is to your north. Do your best to leave your southern sky free of light pollution.  The more free of light pollution, the better – but you don’t have to make a big expedition in order to do this.  While I can see the Milky Way from my backyard, my favorite viewing location is at a bird sanctuary with the ocean to its south about 10 minutes drive away. This spot also has the advantage of an almost clear horizon for 360 degrees!

How? Lie down, look up, nurture your night vision, and put your best binoculars to work.  A blanket, or better yet, a lawn lounge chair will help make this comfortable; otherwise, you’ll find the Milky Way a pain in the neck, and there’s no need for that! “Best binoculars” for this purpose means the ones with the largest diameter lens that you can comfortably hand hold, and that usually means something in the order of 50 mm. But smaller will do the job too. After all, Galileo was the one who showed us the real nature of the Milky Way – the fact that it was actually millions of distant stars and not a faint cloud – and just about any binocular you have will do a better job than the telescope he used. (For more on binoculars for astronomy see this post.)

Most important – guard your night vision! I’m going to suggest you start this exploration early – about 45 minutes after sunset, then stay at it for the next hour or more as the sky darkens above you. If you do this – and if you avoid white light, such as the headlights of cars and the beam of a flashlight – your eyes will naturally dark adapt, and about 45 minutes after you began you should start to pick up the Milky Way, though it may take another 15-30 minutes for you to be able to see it in its full glory.

One more critical “when” note. Choose a time several days after full Moon. When the Moon is waxing – getting larger and brighter each night – it will drown out the Milky Way.  You want to do your early evening Milky Way observing when the moon is waning. This is the couple of weeks after full and really up to the point where the Moon is about two  or three days  old. You need to wait five or six days after full Moon because you don’t want the Moon rising just as full darkness sets in and thus spoiling your view. (In 2009 full Moon is August 5 and good Milky Way observing begins August 11 and continues to about August 23, 2009.)

Where do you look? Up, in a word.

When you set up your blanket or lounge chair do your best to align it on a north-south axis with your head to the north and feet to the south.

What you want to see as you start out is the familiar guidepost stars of the Summer TriangleVega, Deneb, and Altair. These should be familiar because you learned them in June or July. If not, you can learn them now.  They are easy to pick out because as the sky starts to darken they will be the first stars visible, and they will be high in the east. Here’s a chart of what you will see.

Orient yourself north-south, then locate the Summer Triangle high in the east. Click for larger charts. (All charts use screen shots of Starry Nights software which I have then annotated.)

Orient yourself north-south, then locate the Summer Triangle high in the east. Click for larger chart. (All charts use screen shots of Starry Nights software which I have then annotated.)

The brightest – and highest – of the three will be Vega which will be approaching a point overhead. There’s roughly two fists (24 degrees) between Vega and Deneb and nearly four fists (39 degrees) between  Deneb and Altair, so the Triangle is huge. (Our chart is about 90 degrees wide covering from northeast on the left, to southeast on the right. And that real bright “star” near the horizon? That’s the planet Jupiter – at least in 2009. It won’t be in this position other years in August.)

These three Summer Triangle stars roughly bracket the Milky Way – that is Vega roughly marks the western border, Altair roughly denotes the eastern border, and Deneb is about at midstream.  But you need to wait, of course, for it to get darker before you can see the Milky Way.   Right now you’re learning where to look. Do keep in mind that the boundaries of the Milky Way, as with any stream, are not sharp and regular. It tends to meander a bit with little pools of light and some deep, dark areas as well.

But it is early yet. At this point the Milky Way is beyond your reach and probably your binoculars as well. If you have located the Summer Triangle, though, it is time to find the first of our three August asterisms. Remember that an asterism, while it may be part of a constellation, is different. It is a small collection of bright stars and unlike a constellation, it actually will look like the object its name implies.

Use Deneb to start your identification of the Northern Cross. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Use Deneb to start your identification of the Northern Cross. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

The first of these asterisms we’ll use is the Northern Cross, which also serves as a good rough outline of Cygnus the Swan, the constellation which it inhabits.  You find it by starting with Deneb, the middle – and faintest – star in the Summer Triangle. I am assuming it is now more than an hour after sunset and other bright stars are starting to appear. Our Summer Triangle stars are magnitude zero and one – very bright. The Northern Cross stars are magnitude 2 and 3 – dimmer, but about as bright as the stars in the familiar Big Dipper. If you don’t find all these stars immediately, be patient. It may just need to be a little darker. But start with Deneb. It marks the top of the cross, which lies in a general north-south direction. Here’s a chart of the bright stars in this asterism.

Deneb, and the three stars that form the cross bar, should be easy to see.  The fifth star, Albireo, is the dimmest of the group, but note how it is roughly on a line halfway between Vega and Altair, and you should be able to locate it using those two as a guide.  Albireo is magnitude 3 and marks the tip of the cross and even if it is now quite dark, you may have difficulty seeing it in light polluted skies. If so, use your binoculars – and do notice that it does not quite make a straight line with the center star and Deneb.  Also, almost halfway between the center star and Albireo you may notice another, still fainter star that’s a little off this line.

If you want to see this as the swan of the constellation Cygnus, that’s easy enough. Deneb is Arabic for “tail” and marks the tail of the swan. The three bright stars of the cross-bar are the Swan’s wings and the other two stars extending to the south are the Swan’s long neck. Deneb is flying right down the Milky Way – which is what we will do as well, after we locate two more helpful asterisms.

For the first of these next two asterisms, reorient yourself so you are now looking north.

We want to locate  the W of Cassiopeia as it rises in the northeast.  This is a very helpful asterism that also will help you locate the North Star.  Much of the time, of course, we use the Dipper and its “Pointer” stars to find Polaris, the North Star. But as we move into the fall the Dipper gets lower and lower in the northwest. In my backyard it eventually sinks beneath trees. But no worry – as the Dipper goes down the W  of Cassiopeia rises and it is a perfect counterpoise to the Dipper. Like the Pointer stars, it is about 30  degrees –  roughly three fists – from Polaris, so I think of it as marking the other side of a huge circle going around the North Star. The Dipper marks one side of that circle, the W the other. Here’s the appropriate chart. (To see an animation of how these stars move around the North Star, see this post.)

Look north and you'll see the W of Cassiopeia rising in the northeast. The last star of the W - the one closest to the horizon - is the faintest and may no tbe visible at first. Click to enlarge this chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

Look north and you'll see the W of Cassiopeia rising in the northeast. The last star of the W - the one closest to the horizon - is the faintest and may no tbe visible at first. Click to enlarge this chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

But for our purposes on this August night we shall see the W as marking the northern extremity of the Milky Way. Oh the Milky Way  continues up here – but it does get fainter and a little harder to pick out.  Still, you should think in your mind of a river running through the W of Cassiopeia through the Northern Cross – or Swan – and on southward past Altair, the southern-most star in the Summer Triangle.

And where does it go? Why into the Teapot of course!  For those in mid-northern latitudes, which is where I am, the Teapot asterism tends to sit on our southern horizon – and some of the best and brightest parts of the Milky Way look like steam coming out of its spout! So turn around now and face south. For me, the Teapot is just 15-20 degrees off the horizon – roughly two fists – but if you live farther south, say about latitude 25 degrees, then it will be significantly higher.

Here’s what you should be  looking for:

You canbt hink of the Milky Way as streaming into the Teapot - or you can think of it as the steam coming out of the Teapot - which ever helps you remember best where to look.  Click for a larger chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

You can think of the Milky Way as a river streaming into the Teapot - or you can think of it as the steam coming out of the Teapot - which ever helps you remember best where to look. Click for a larger chart. (This chart uses a screen shot from Starry Nights software which I have then annotated.)

The Teapot is the core of the constellation Sagittarius, and it follows the familiar scorpion of Scorpius. You may have found that last month when you located another of our guidepost stars, Antares. Now, as you look south –  it also should be quite dark by now – you should have no trouble seeing the second and third magnitude stars that form the Teapot, or for that matter, the wonderful curves of the scorpion to its west.

Now, if it is more than 90 minutes after sunset and if you are in a location away from light pollution and, of course, are enjoying one of those crystal clear nights with dark-adapted eyes, then you also should be seeing the Milky Way. It only takes time and patience for you to trace it out – to see areas that are brighter than others – as well as some dark patches that don’t mean the absence of stars, but the presence of obscuring dust. But don’t think of the dust as getting in the way – think of it as star stuff – for what you are seeing in many sections of the Milky Way are the parts of our galaxy where new stars are being born. Relax and explore with your binoculars – start to absorb the majesty of millions – no billions – of stars! Here’s an overview from the W through the Northern Cross to the Teapot. If conditions are right – and you have a dark sky – it will look to the naked eye like faint clouds that get brighter as your eye traces them out from north to south.

The August Milky Way appears as a cloudy area in this sweeping overview  showing a fully dark sky. By all means, click for a larger image of this chart.  (This chart use

The August Milky Way appears as a cloudy area in this sweeping overview showing a fully dark sky. By all means, click for a larger image of this chart. (This chart use

But what if you are in a typical, light-polluted, suburb? You’ re looking in the right spot, but you see no star clouds, only a handful of bright stars. Don’t despair. If you have located  the three asterisms – the W to the north, the Northern Cross overhead, and the Teapot to the south, then you are looking at the Milky Way even if you can’t see it.  Assuming it is at least 90 minutes after sunset, now is the time to start exploring with your binoculars. (You should do this even if you can see the Milky Way well with your naked eye.)

Start with the center of the Northern Cross and sweep from left to right – east to west – across the three stars that mark its cross arm.  When you’re on the center star of these three you should see lots of fainter stars in your binoculars – but as you get out beyond the stars that mark the ends of the crossbar, you should see fewer. Do broard sweeps with your binoculars being conscious of the background hue.  Away from the Milky Way it should be darker – if you notice it lightening as you move across the Milky Way – wall, that’s the Milky Way.  Remember to think of the Milky Way as a river running roughly north to south from the W to the Teapot – to find its borders, keep sweeping across it in an east-to-west direction as you also move slowly southward. (Looking at the background hue, however can be deceptive. You have to separate the change caused by the Milky Way from the change of say the light dome of a nearby city, or other source of bright light. The sky, for example, will appear lighter as you approach the moon. But then, trying to find the Milky Way with the moon in the sky isn’t a real good idea as mentioned earlier.

And what is it you are seeing and why does it appear this way to you? That’s the important question. And this is where you have to do some mental gymnastics.

Think of our galaxy as a large pizza pie with extra cheese and goodies heaped in the center.  Now put yourself away from that center – perhaps one-half of the way towards one edge and buried down at the level of the crust. That’s a pretty good simulation of our galaxy and our place in it. You really need to get outside it – we can only do this in our imaginations – and look at it from that perspective. If we could get outside it, here’s approximately what we would see:

Two view of our Galacy, the Milky Way. The one on the left is from aposition above it, the one on the right shopws you the galaxy edge-on. This is a screen shot from the wonderful, free software, "Where is M13."

Two view of our Galacy, the Milky Way. The one on the left is from aposition above it, the one on the right shopws you the galaxy edge-on. This is a screen shot from the wonderful, free software, "Where is M13."

The image on the left is how we think our galaxy would look if we could get above it and look down on it – like a big pinwheel of stars.  And what if you could see it edge on? Well, that’s the picture on the right. (This is a screen shot  from a wonderful – and free – software program called “Where is M13” that helps you understand where various objects really are in relation to us and the rest of the galaxy.)

OK – focus on the edge-on image – and note how really thin most of the galaxy is. It is about 100,000 light years across, but on average just 1,000 light years thick.

plane_view_MW

Now imagine yourself on a small dot (the Earth) rotating around that small dot in our image – the Sun. Do you see a lot of stars when you look “up” – that is, look in the direction of the words  “The Sun.”

No – in fact, if you look down, you don’t see many stars either – or for that matter, if you look in just about any direction there are relatively few stars visible to you. Why? Because the disc is just 1,000 light years thick, and most of the time you’re looking right through it the short way.  But  look along the plane of the galaxy – say  directly to the right or left – and what a difference!

Looking to the left you see many stars – in fact, a thin river of stars. Looking this direction, you’re looking through about 20,000 light years of star-filled space. We are looking along the plane, generally towards the outer rim, when we look at the W of Cassiopeia. Look along the plane to the right, and you see even more stars in a much wider river. Now you’re looking through about 30,000 light years of star-filled space and then right at the star-rich, galaxy core. And this, in a general way, is what we are doing when we look toward the Teapot of Sagittarius. That’s why the Milky Way is so much brighter and denser in that direction.

Not too difficult to understand – but this is only a rough sketch. As recently as 2008 scientists came up with a much different perspective of our galaxy than we had had up until then. Prior to the latest study, we thought the galaxy was a spiral with a bulge in the center and four main arms. Now we see it as a barred spiral – that is, the bulge in the center looks more like a bar that spills into two – not four – main spiral arms. There are other smaller arms in the spiral, and it all gets quite complex.

The problem, of course, is there is no way we can get outside our galaxy and look in. The distances are incredibly vast. Even if we could send a space probe at the speed of light, it would be thousands of years before it got outside our galaxy, took some pictures of us, and sent those pictures back. So we have to try to decide what the galaxy really looks like from the outside by studying it from the inside. Imagine, for a moment, being inside your body and trying to figure out what you look  like by what you can see from the inside, and you get an idea of the problem. Fortunately we can see other galaxies and in later months we’ll be looking at one that looks a lot like what we think ours would look like if we could only get outside it and look back.

Meanwhile, relax – look up – and dream of all  the wonders that are out there and sending their messages back to you in the form of millions of tireless photons that have travelled thousands of year to reach your eyes and ping you brain on this dreamy August evening.  Harvest some of those photons by surfing the Milky Way with your binoculars. You will notice that in some areas it is quite dense and you may even discover some tiny, tight clusters of new stars – or a globular cluster of old stars, or even a little hazy patch where new stars are being born.  You need a telescope to see these well, but you can just discern some of them with binoculars, and with telescope or binoculars, what you really need to see with is your mind’s eye. Knowing what you are looking at is what brings this faint cloud alive and turns it into the awesome collection of billions of stars – and more billions of planets –  that it is.

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