August 2012 – Mars, Saturn, Spica in the west – and a spectacular Perseids shower

Should you watch the planet show in the West in the evening? Or the meteor shower in the morning? Why not both? And if you’re getting up early to see the Perseids at their best, be sure not to miss brilliant Venus and Jupiter – well, how could you?

Over in the west we have Mars showing you how fast a planet can appear to move as it runs between  Saturn and Spica – over a period of three weeks making a colorful red, blue and yellow display.  And all over the sky for several days this month you are likely to pick up a brilliant, Perseid meteor – but particularly on the morning of the 12th of August with the 13th a good back-up – and this year’s show should be especially good because the Moon will not put in an appearance until early morning and will not be bright enough to ruin the show.

Let’s start with the west – week-by-week the changing scene will look like this low in the southwest about an hour after sunset:

The circle is 7 degrees – roughly what you can expect from a low power binocular view.

 

A fun night because a young, crescent Moon joins our trio.

You will need a clear and unobstructed  western horizon for this one because these three objects are roughly 10 degrees – one fist – above the horizon. (Early in the month they’ll be a bit higher – late in the month they get quite low.  Now what I love about this event is it demonstrates three things -

• Color in the sky – Saturn is yellow, Mars, Red, and Spica blue. But these colors are subtle. You’ll see them better if you use binoculars and you might want to review this post on star colors to better know what to expect.
• Perception and the effect of motion – from night to night Saturn will hardly appear to change positions relative to the background stars at all,  and Spica won’t  change – but Mars will whip right along and this will be amply clear as you check it’s position against the other two.  The reason is simple – Mars is much closer to us at about 158 million miles; Saturn is about 939 million miles and, of course, Spica is so far away we measure its distance in light years – 263.
• The time dimension is on display as well – Mars is roughly 14 light minutes from us, Saturn is  well over a light hour, and Spica  263 light years. So what appears to be a two dimensional scene is revealed to be three dimensions as you observe the rapid motion of Mars and picture the solar system – and when you put your mind to it, you understand that the instantaneous nature of the scene is an illusion – that you are really looking into the fourth dimension and what happens simultaneously from your perspective is really happening at much different absolute times.

To help grasp the situation, take a look at this Orrery view of the Solar system for August 7. Keep in mind two things. The east-to-west motion we see as the night goes on is due to the spinning of the Earth.   The night-to-night westward – downward – drift of all  is caused by the motion of the Earth in its orbit around the Sun.

Orrery view for August 7, 2012, (Click image for larger version.)

The yellow arrow in the image above shows our view of Mars and Saturn in the evening sky. As the Earth rotates counter clockwise on any given evening, first Jupiter, then Venus come into view in our morning sky – red arrow.  If you then picture the Earth moving ahead in its orbit it’s not hard to understand why Saturn and  Mars will eventually be lost from view, while Jupiter will appear earlier each evening. Venus is a bit more complex. It too will get lost in the glare of the Sun, but since it is moving faster than us the change will appear to take place fairly slowly. Maybe I’m just slow, but it has taken me years to move from these abstract representations of what we see in the sky and how the planets are moving, to get to the point where I can look up and have a genuine, intuitive sense of what’s going on. Very satisfying and worth the effort, but even if you don’t do that, it’s a wonderful show! (The Orrery view is obtained from Solar System live web site. Go there and play with the dates to see the changing motions of the planets.)

Perseids in the morning

OK – so much for the evening sky. The morning sky is really spectacular because we’re looking at a section of sky that contains a lot of our brightest stars and  two terrific star clusters, plus the two brightest planets. What backdrop for a brilliant meteor shower!

The red oval represents the area opf the sky from which the Perseid meteors appear to radiate – however, they can go in any direction from here and might appear any where in the sky. (Click image for larger version. Prepared from Starry Night Pro screen shot.) Here’s a quick guide.

Perseids – a quick guide

When:

The night of  August 11-11 starting about 90 minutes after sunset, but best after midnight. And if that night is likely to be cloudy, the next night of August 12-13 might prove to be just as good, but the best chance looks like the 11-12. (There’s no doubt you should see meteors either night – but there is doubt as to exactly when the shower will peak.)

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. My most memorable Perseid skimmed the horizon to the north.

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 down swing, but because we’ll have little interference from the Moon, this should be a better than average year.

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 meteoroid-rich area.  We call this occasion a meteor shower. (For your dictionary: A meteoroid 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! Consider this: 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.

Look east in August 2012 – 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. (OK – actually most of southern New England!)

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 2012 your best views will come between August 6th and 22nd - on other dates the Moon is more likely to interfere. Of course, when the Moon is young and waxing you can always wait for it to set – and when it is old and waning  you need to make sure it hasn’t risen yet. For a Moon calendar for any month go here.  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 Triangle – Vega, 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:

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.

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.

• To learn more about the “W” of Cassiopeia go here.
• To be the first on your block to build a scale model of the Milky  Way, go here!

Look North In August 2012 – 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 eminently 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.

Luna-See – Let the Moon of August 2011 be your guide!

Anyone can find the Moon – so why not use it to help you learn the sky?

Moon and Mars in the early morning sky, August 25, 2011.

Each month the Moon in its travels comes near some planets, bright stars, and asterisms. If you look on the right night this month you’ll be able to use the Moon to help you find:

• Saturn and Spica (August 2, 3 & 4)
• Antares and the Scorpion (August 7)
• The Arrowhead with the asteroid Vesta (August 13)
• The Hockey Stick and Jupiter (August 19)
• Pleiades, Hyades, & Aldebaran (August 22)
• Taurus (August 23)
• Mars with the heavenly twins, Castor and Pollux (August 25)

Whew! That’s a whole lot.  And you’ll find when and exactly where to look by using the charts below. You have to pick the right night and you have to  be ready to approximate – the charts are a rough guide as to when and where to look – and use binoculars to help you find otherwise bright stars because the Moon light will tend to wash out  all but the brightest.

I say “rough guide” because these charts are all for my specific location on the Northeast Coast of the United States. The moon moves about half a degree (its diameter) an hour, so observers on the West Coast will see it in a little different location than I do. But the charts should give a good general guide and help you know the night sky better – and as a bonus you’ll begin to develop a feel for the rather complex motion of the Moon each month.

Notice that for the first half of the month the Moon is in the early evening sky. For the second half it is in the morning sky. The Moon’s image in the charts is about three times as big as it actually is in order to show the phase clearly.

Click any chart to get a larger version. All charts are prepared from Starry Nights Pro screen shots.

Saturn and Spica, (August 2, 3 & 4)

Antares and the Scorpion (August 7)

The Arrowhead with the asteroid Vesta (August 13)

The Hockey Stick and Jupiter (August 19)

Pleiades, Hyades, & Aldebaran (August 22)

Taurus (August 23)

Mars with the heavenly twins, Castor and Pollux (August 25)

Moon phases

• New Moon  - July 31
• First Quarter – August 6
• Full – August 13
• Last Quarter -August 21
• New Moon – August 28

Look east! In August 2011 – 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 Triangle – Vega, 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:

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.

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.

• To learn more about the “W” of Cassiopeia go here.
• To combine your Milky Way viewing with a shower of shooting stars, go here!
• To be the first on your block to build a scale model of the Milky  Way, go here!

Look North In August 2011 – 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.

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

• Vesta and Other Asteroids
• Details of the Dawn Mission
• Goodbye Saturn, Good Evening Jupiter, Good Morning Mars!

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.

- Enlarge image

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

• Perseids
• Planets
• Calendar  (summary)

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 Triangle – Vega, 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:

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.

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.

• To learn more about the “W” of Cassiopeia go here.
• To combine your Milky Way viewing with a shower of shooting stars, go here!
• To be the first on your block to build a scale model of the Milky  Way, go here!