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    My Journey through the Astronomical Year

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

. . . and Saturn’s rings vanish too!

Yes they do – and they do it this week (September 4, 2009) , and it’s fascinating, too – but not nearly so easy to observe as Jupiter and its moons – unless you’re int he southern hemisohere.

I had been so wrapped up in the vanishing  act of Jupiter’s moons this week I had forgotten that this is also the week that Saturn’s rings vanish as well! Then today Spaceweather.com published a wonderful little video – not a simulation, but  a real picture animation made by an amateur – showing our changing perspective of the ring system over a period of several years. You can see it here. Spaceweather.com introduces it this way:

On Sept. 4, 2009, Saturn will turn its rings edge-on to Earth, and for the first time in 14 years they will seem to disappear. “To mark the occasion I’ve made an animation combining six years of Saturn observations,” says New York amateur astronomer Alan Friedman. “It shows the changing plane of the ring system as viewed from my Buffalo backyard from 2004 to 2009

Now this really isn’t as much of a shocker to me as the Jupiter’s moon act  simply because the rings have been slowly getting more and more difficult to see and were actually edge on for a period in August  – and because while Saturn is still visible, it’s very, very difficult to see – and dangerous – because it is so close to the Sun.  At sunset on September 4 it will be just 4 degrees from the western horizon and will set 25 minutes after the Sun for my location at 42-degrees north.  That means you need a sparkling clear western horizon, rare indeed, to see it.  Yes,  sophisticated telescope users will tell you that you can see planets in daylight and you can. But when something is this close to the  Sun that’s far too close for comfort and safety as far as I’m concerned.  Make a slight mistake and you get an unfiltered glimpse of the Sun and that will damage your eyes for sure, if not  blind you. For what? To see Saturn without it’s rings? Nope. Not for me. Though it is rare enough – it won’t happen again for 16 years – it just doesn’t have the same appeal to me as Jupiter’s moons.

The long term phenomena is interesting – the animation put together of it is terrific and instructive. Enjoy this event that way. Here’s the link once more. But live viewing? Not worth the try this time from my perspective unless you live in the southern hemisphere. From Sydney, Australia, for example, Saturn will be a respectable – though challenging – 10 degrees above the western horizon at sunset. Thirty minutes after sunset Saturn will still be about 4 degrees above the horizon, beneath a slightly brighter Mercury which will be about 17 degrees high.  I love Saturn – and I love it for its rings. But I’ll wait to greet it again until at least October, but more likely November. Then it will be solidly above the horizon an hour or more before dawn – and yes, it’s rings will be visible then, as once more we’re at an angle to the huge planet so we can see them. Meanwhile, I’ll let Jupiter play its role as the King of Planets, well placed high in the early evening sky and I’ll continue to enjoy the dance of its moons.

Jupiter’s moons pull a vanishing act – and other neat dance moves!

(For an observing report on this event, go here.)

Jupiter’s four bright moons always put on a great show – ask Galileo – changing positions slowly in the course of the night. But for viewers in North America the night of September 2-3 offered an unusual opportunity because the four bright moons all played hide-and-seek at once – something that happens  about 20 times a century and I suspect much less for any given geographic area. That said, the following video and text I believe remainr elevant andhelpful for anyone interested in watching Jupiter’s moons. The  video is an animated simulation depicting events of one night. It was created in Starry Nights Pro astronomy software and time has been speeded up so  that what you see in about four minutes is what actually takes place in about seven and a half hours.

(For a complete explanation of what’s going on in this animated simulation – and what you should see September 2-3, 2009 – you can take this shortcut  to  the sequence of events below.)

Here’s why I love watching  Jupiter’s four brightest moons:

  • You can see them with any small telescope – even binoculars if you can hold them real steady.
  • They do something! Most astronomical objects don’t change much over our lifetimes. Jupiter’s moons, as you can see from the video simulation, go through significant changes in a single night.
  • These four bright moons played a major role in changing our view of the universe.
  • They even helped us determine the speed of light a couple hundred years ago, something next to impossible to determine on Earth without modern, sophisticated instruments.
  • For the telescope user they:
  1. duck in and out of Jupiter’s shadow (eclipse)
  2. hide behind the planet and suddenly pop out (occultation)
  3. cross in front of the planet providing a challenge for telescope users to spot them  (transit)
  4. and from time to time they cast their shadows on the giant planet – shadows visible in a backyard telescope as pefect round circles
  • Hubble and modern spacecraft have shown us that Jupiter’s moons are full of surprises.  No two are alike and all four are different than what scientists imagined before the spacecraft got out there and gave us an up close and personal view.
  • All of which is incredibly awesome when you understand that the little lights you see moving with grace, precision, and predictability are complete worlds in themselves the size of our moon or larger. (Ganymede is about 1.5x the diameter of our moon.) Newton is playing the tune, and the moons do the dance – music of the spheres indeed!

jupiter_moons

You can enjoy Jupiter’s bright moons any night the planet is visible. What’s special about the night of September 2 and 3 of 2009 is they’re going through their complete routine in one night and for a couple hours all four of them are out of sight for all practical purposes, but still providing an interesting challenge for the telescope user. What’s more, Jupiter is very close to the moon on this particular night  and very bright in the southeastern sky,  so it is easy to find. And any small telescope will reveal the moons. Seeing them with binoculars is possible, but it takes sharp eyes and a steady hand. I’ve never been able to see them with binoculars unless I can steady the binoculars on a tripod, or against the corner of a building or some other support.

The moons were discovered by Galileo 400 years ago and he didn’t waste any time writing about his findings in his “Starry Messenger.” What he had to say shook up the religious/philosophical/scientific establishment of the day. Although Copernicus had argued otherwise more than 50 years before, the common belief remained that the Earth was the center of the universe and everything revolved around the Earth. But a few nights of observing Jupiter’s moons and that whole business of us being at the center of everything went out the window. Obviously Jupiter was at the center of its own little system and these moons were revolving around it, not us.

The  13-day-old Moon and Jupiter dominate the eastern sky near the horizon for North American observers on September 2, 2009. This screen shot from Starry Nights software captures the positions, but don't get the idea that Jupiter looks thatbig - the size represents its brightness - and its is fa rbrighter than any of the stars, though to the naked eye it will look like a star.

The 13-day-old Moon and Jupiter dominate the eastern sky near the horizon for North American observers on September 2, 2009. This screen shot from Starry Nights software captures the positions, but don't get the idea that Jupiter looks that big - the size represents its brightness - and its is far brighter than any of the stars, though to the naked eye it will look like a star.

Now, with any small telescope, you can travel in the footsteps of Galileo, observe Jupiter’s moons, and make your own drawings. This month (September, 2009) is a good time to start because Jupiter appears in our eastern sky as the Sun is setting in our western sky. By about half an hour after sunset Jupiter will put in an appearance. The only thing brighter than it in the eastern evening sky this month is the moon. And on the evening of September 2 folks in North America will see a nearly full moon pretty close to Jupiter – exactly how close depends on where you are and when you look. On the East Coast at 8 pm EDT the moon will be less than 3 degrees from Jupiter in the southeast and pretty close to the horizon. About 7 hours later it will be in the southwest and the moon will still be with it, but the separation will have increased to about five degrees. (Typical binoculars have a field of view of about 7 degrees, so you should easily see both the moon and Jupiter in the same binocular field.  The question – which I honestly can’t answer – is how easy will it be to see Jupiter’s moons with our own moon shining so close to it? Will the moon drown them out? I’m pretty  confident this won’t be a problem for telescope users. It may make it  difficult for binoculars users since the moons of Jupiter are roughly as bright as the faintest stars we can see with our naked eye.)

What should you look for an when?

First, if you want to know which of Jupiter’s moons is where on any given night, use this neat little online utility provided by Sky and Telescope magazine.

Now the basics. Jupiter has 63 moons, but only four of them are easily seen in small telescopes. Here are their names – in order moving outward from the planet – and links to more details about each.

Sequence of events September 2-3

Here is the schedule of events in  EDT, with  24-hour format Universal Time in parenthesis. (Data is from a listing in the September Sky and Telescope.)  If clouds, sleep, or work cheat you out of a live view, you still might refer to the following list as you watch the animation.)

September 2

7:19 pm (23:19)Callisto is occulted – goes behind the planet. (This will be in daylight for US observers, but when you start observing Jupiter later,  know that Callisto is already behind it.)

11:43 pm (3:43 Sept. 3) Io is occulted – goes behind the planet. (This is fun to watch – how long does it take Io to vanish? )

11:58 pm  (3:58 Sept. 3)Europa transit begins on the opposite side of the planet from where you saw Io vanish a few minutes before. Seeing the moon against the bright disc of the planet is possible in small telescopes, but varies in difficulty depending on exactly what part of the planet is behind the moon, some parts being darker in hue than others. But keep in mind, these moons are so far away that even in a large, backyard telescope they barely show a disc under ideal conditions. So what you are look for is a point of light not much different than a star.

September 3

12:43 am (4:43)Ganymede follows Europa onto the planet’s disc. Is it easier to see than Europa? It’s significantly larger, so might be a tad easier, but again, it takes a large telescope to show the moons as even a small disc.

12:56 am (4:56)Europa’s shadow follows it onto the face of Jupiter – but it may be easier to see as it gets nearer the center. It also may help you pick up the disc of Ganymede – the shadow of Europa during the first half of its journey is very close to the disc of Ganymede – at least as shown by the Starry Nights Pro simulation.

2:29 am (6:29)Io pops back into view – but look where it is! It’s not close to the planet when it does this because after it was hidden by the disc (an occulation) it went into the planet’s shadow – technically, an eclipse. So what you see is it emerging from the shadow, already some distance out from the planet.

2:42 am (6:42) Ganymede’s shadow enters the disc.  Notice how far behind Ganymede it is? Europa’s shadow was much closer to it. Why? Because Europa is much closer to the planet then Ganymede and here’s proof!

2:49 am (6:49) Europa emerges from the disc – but if you have not been able to follow it when it was on the disc it may be difficult to pickup for few minutes because it will still be close to Jupiter and lost in its glare – at least to the smallest telescopes and binoculars. However, Europa’s shadow will still be visible on the disc for almost another hour.

3:47 am (7:47) Europa’s shadow goes off the disc.

At this point East Coast observers are seeing a Jupiter that is very close to the southwestern horizon and the moons will be difficult to observe. For my location – at 71 degrees longitude (Westport, MA). the giant planet sets about 4:30 am.

4:20 am  (8:20)Ganymede’s transit ends, but it’s shadow is still on the planet.

4:35 am (8:35) – At last! Here comes Callisto! For me it has been out of sight all night. It goes behind the planet before it is dark enough to see it and doesn’t come out until after Jupiter has set. However, folks farther west should certainly see this exit event.

6:21 am (10:21)Ganymede’s shadow exits the planet’s disc. Hey – that’s all folks – for tonight. But there are many other nights when there are interesting events.

Be sure to check Sky and Telescope Javascript utility.  Any night Jupiter is well placed for observing I always check this little utility to see if there are any neat events coming up at a convenient time. Nights like September 2-3, 2009 are rare. But with four moons there are frequent times when one or the other is doing something interesting.

How to time a light beam!

Oh – and about determining the speed of light. Think about it.  I believe Galileo once took a stab at this by stationing observers facing one another from different mountain peaks. They then uncovered a lantern at a predetermined time.  No luck. Light is much too fast for this kind of experiment. Hey – light could go completely around the Earth more than seven times in a second! But here’s how Jupiter’s moon helped determine the speed of light more than 300 years ago! These kinds of discoveries always leave me in awe at how brilliant the discoverer’s were and how precisely they were able to make observations with tools that were not nearly as good as the inexpensive telescopes available to anyone today.  The  account which follows can be read in full here. It is from a posting by Michael Fowler of the University of Virginia Physics Department. One more thing to appreciate as you watch Jupiter’s moons.

The first real measurement of the speed of light came about half a century later, in 1676, by a Danish astronomer, Ole Römer, working at the Paris Observatory. He had made a systematic study of Io, one of the moons of Jupiter, which was eclipsed by Jupiter at regular intervals, as Io went around Jupiter in a circular orbit at a steady rate. Actually, Römer found, for several months the eclipses lagged more and more behind the expected time, but then they began to pick up again. In September 1676, he correctly predicted that an eclipse on November 9 would be 10 minutes behind schedule. This was indeed the case, to the surprise of his skeptical colleagues at the Royal Observatory in Paris. Two weeks later, he told them what was happening: as the Earth and Jupiter moved in their orbits, the distance between them varied. The light from Io (actually reflected sunlight, of course) took time to reach the earth, and took the longest time when the earth was furthest away. When the Earth was furthest from Jupiter, there was an extra distance for light to travel equal to the diameter of the Earth’s orbit compared with the point of closest approach. The observed eclipses were furthest behind the predicted times when the earth was furthest from Jupiter.

From his observations, Römer concluded that light took about twenty-two minutes to cross the earth’s orbit. This was something of an overestimate, and a few years later Newton wrote in the Principia (Book I, section XIV): “For it is now certain from the phenomena of Jupiter’s satellites, confirmed by the observations of different astronomers, that light is propagated in succession (note: I think this means at finite speed) and requires about seven or eight minutes to travel from the sun to the earth.” This is essentially the correct value.

Less successful was an idea they had much later that they could solve the problem of finding one’s longitude – while at sea – by observing the moons of Jupiter. This was very seriously pursued  because knowing longitude is critical to navigation and the accepted method involved using a very precise clock that kept correct time throughout a long sea voyage. It was hard enough to make a very precise clock – but one that retained its precision when subjected to the knocking about and unavoidable moisture that was part of any long voyage by sail? Nearly impossible. (See the wonderful book, “Longitude,” by Dava Sobel, for the story of how they did solve this.)  But that said, as you watch the moons of Jupiter with a small telescope, try to imagine doing this on the heaving deck of a sailing ship with a telescope that is significantly cruder than the one you buy today! Then imagine that your life may depend on the result! Makes you appreciate GPS if nothing else 😉


Making free, custom charts for your night sky

Exactly what you see in the night sky depends upon where you are on Earth. The charts used on this  Prime Time web site are primarily for those living in mid-northern latitudes. But you can easily create free charts for your observing location. What’s more, you can customize these charts  so they meet the Prime Time goals of learning the bright stars and selected asterisms as they rise in the east. This post will show you how.

We all live on a ball and we look out at the “dome” of the sky as if we were living inside a globe. This means that exactly what we see and when we see it depends on where we live. If you live near mid-northern latitudes – that is, if you live in the highlighted area shown in the map below – the star charts and information  on the Prime Time web site should be very helpful to you because your night sky will look much the same as mine.

This map shows that by centering on 40 degree north latitude as a viewing location  our charts will work reasonably well for a large portion of the world's population that lives in the northern hemisphere. Outside that rgeion you need to make significant adjustments - and the southern hemisphere is another story entirely. Sorry ;-(

This map shows that by centering on 40 degree north latitude as a viewing location our charts will work reasonably well for a large portion of the world’s population that lives in the northern hemisphere. Outside that region you need to make significant adjustments that, fortunately, are easy with the free chart maker described here.

But if you live in other sections of the northern hemisphere – or even in the southern hemisphere, I urge you to follow the instructions below to create your own charts. In fact, you may find it interesting to try this free online chart source no matter where you live because then you can generate your own charts for your specific needs of the moment. Even if you live in the southern hemisphere, this chart-making Web site will be of use to you, though many of my specific examples on Prime Time will be of limited use. This is because  southern hemisphere dwellers, while seeing  many of the same stars and constellations that those of us in the northern hemisphere see, will see these stars at different times, and in different parts of  the sky than mentioned on Prime Time – and, the bright asterisms I give as guides may be hard to recognize since their orientation can be entirely different when seen from the southern hemisphere. Still, the basic principle of learning the brightest stars as they come out 45 minutes after sunset, rising in the east, holds.  The charts you make will help you do this.

Exactly how your view of the sky changes is complex and depends on not only where you are looking from, but what area of the sky you’re looking at.  When looking due south or north, the changes are most dramatic – looking due east, as we urge you to do when learning the sky, the changes are less dramatic, but still can be confusing. What follows are charts created with the Your Sky online chart maker. All are for 45 minutes after sunset (local time) on August 1, 2009, and all are the view when looking due east. The Prime Time goal in this instance is to learn the three bright stars of the “Summer Triangle”  – Vega, Deneb, and Altair. But notice how the position of these stars in the sky changes  – and the orientation of the triangle they form changes as well, depending on your viewing location.

Here's what I see in my eastern sky from near Boston, MA and this is the default view for charts on this web site.

Here's what I see in my eastern sky from near Boston, MA, and this is the default view for charts on this Web site.

Viewing from Anchorage, Alaska looks very similar to view from Boston, but notice how the orientation has changed. The other big change for Anchorage is on August 1 you will be in perpetual twilight - your night never gets fully dark at that time of year. That's good for learning bright stars, but hard when you wnat to look at faint objects.

Viewing from Anchorage, Alaska, looks very similar to the view from Boston, but notice how the orientation has changed? The other big change for Anchorage is on August 1 you will be in perpetual twilight - your night never gets fully dark at that time of year. That's good for learning bright stars, but hard when you want to look at faint objects, such as the Milky Way.

ys_miami_st

In Miami. Florida, the sky appears to make a small shift to the north. That shift brings into view on this particular date the planet, Pluto - but you will NOT see this with your naked eye, or even with binoculars. It takes a fairly large telescope and plenty of patience to find Pluto. (The bright planets that do sometimes appear in the east shortly after sunset are Mars, Jupiter, and Saturn.)

And now the view from “down under” – the southern hemisphere!

In Sydney, Australia th eview canbe quite different. You will see the same bright stars and the "Summer Triangle," but not for an hour or two later. Notice that one star - Altair - is just putting in an appearance on the horizon. The other will rise in the northeast for viewers in Sydney, but quite a while after sunset. Meanwhile, on this same date viewers in Sydnet are seeing the moon in their eastern sky - and if they have a telescope and lots of patience, Pluto.

In Sydney, Australia, the view is quite different. You will see the same bright stars and the "Summer Triangle," but not for an hour or two later. Notice that one star - Altair - is just putting in an appearance on the horizon. The others in the triangle will rise in the northeast for viewers in Sydney, but quite a while after sunset. Antares is also a guidepost star that we introduce in June, but is not visible in the eastern sky of our northern locations. Meanwhile, on this same date viewers in Sydney are seeing the moon in their eastern sky - and if they have a telescope and lots of patience, Pluto.

The Web site that generates these custom charts is called Your Sky, and while it includes excellent directions, the directions that follow are aimed at helping you generate custom charts that complement the Prime Time approach to learning the night sky – charts such as we include here, but that match your location. Making your first chart may take 10 minutes – but when you return to make others you’ll find it quick and easy.

Remember there are three critical elements to the Prime Time learning method:

  • focus on only the brightest stars and easily recognizable asterisms
  • observe objects as they appear to rise in the east
  • begin each observing session 45 minutes after sunset so you learn to find these bright stars and asterisms as they come out and before the sky is cluttered with many fainter stars.

So when you customize the charts on the Your Sky Web site using the instruction which follow, the goal is to optimize the chart for this use.

Preliminaries

You will need to know your latitude and longitude rounded to the nearest degree. If you don’t, go here (opens in new window/tab). Be sure to note whether your latitude is “north” or “south” and whether your longitude is “east” or “west.”

Remember to start your observing session 45 minutes after local sunset. To find the time of local sunset anywhere in the world for any date go here.

You will need to know the time and date you plan to observe in Universal Time – which used to be called Greenwich Mean Time. Most web sites and books give directions for changing Universal Time to your local time. Thus the conversion factor for Eastern Daylight Savings Time is usually given as  -4 – which means you subtract 4 hours from Universal Time to get EDST. For creating  star charts at Your Skies, you need to go in the opposite direction. To get the conversion factor for your time zone go to this web site.  (Universal Time is commonly used for astronomical events so that anyone, anywhere in the world, can thus calculate the local time for an event. You will find frequent use for it when you observe the night sky.)

Finally, planets on the Your Sky charts are identified by their common symbols show, in this graphic from NASA.

planet_symbolsI highlighted the three planet symbols most important to us – Mars, Jupiter, and Saturn – because these are the three bright planets that sometimes appear in our eastern sky after sunset and so may get confused with a bright guidepost star.

Step-by-step chart making

  1. Go to the Your Sky Web site. (Link opens in a new window/tab.)
  2. Scroll down to the “Horizon View” section and click “Make Horizon View” button.  At this point the settings do not matter.  Just press the button and don’t panic when you see the rather cluttered chart – you are going to modify your settings significantly in the form below the chart, then update it.
  3. Scroll to the form below the chart. You want to make it look much like the form to the right – but with your location and time. (Click the image of this form for a much larger view in a new window or tab.)
  4. You should uncheck most of the choices on the form to customize this chart. Here are the choices you want to make and what to put in each box. (The form at right is filled out in this way, but you need to substitute your specific information.)

    Click image of form to get a larger view in a new window or tab - you can then switch back and forth between windows, or print this new image out to help guide your choices.

    Click image of form to get a larger view in a new window or tab - you can then switch back and forth between windows, or print this out to help guide your choices.

  • Choose Universal Time and put in the Universal Time for the date and place where you will be observing. Remember to start your observing session 45 minutes after local sunset. (See “preliminaries” above for Universal Time and time of local sunset)
  • Your Viewpoint will be in “azimuth” and  set to 90 degrees. That means you’re looking due east.
  • Set the Field of view for 90 degrees. This will cover your horizon from northeast to southeast. (If this doesn’t capture what you want, you can increase the viewpoint to 180 degrees, but this tends to distort. You may want to change the azimuth instead – “0” would be north; “180” would be south. And notice the “pan” buttons just below your chart that allow you to move your view to the right or left.)
  • Set the latitude and longitude for your Observing Site.  (See preliminaries.)
  • Leave most of the “Display Optionsunchecked. You want a simple map.
  • Moon and planets”  should be checked because if there are any bright planets in the east they will look like stars and confuse you if not identified.  Planets are “wanderers” and one month may be there, and the next not. There are just three  bright planets  that might appear in the eastern sky in the early evening –  Mars, Jupiter, and Saturn.  (Mercury and Venus are seen only in the western sky in the early evening, or the eastern sky in the early morning.)
  • The important settings are for the stars. Set “Show stars brighter than magnitude” to 3.5 – and check “Names for magnitude” and set it for 1.5 and brighter.  The first setting means that all the stars of the bright asterisms we use will be included, but none of the dimmer stars which aren’t visible until the sky is fully dark and generally add confusion. By naming stars brighter than magnitude 1.5 you will have names for all the guidepost stars we use with the exception of Polaris, the North Star – to have that named you would need to set this to 2.5 and be looking north (0) not east (90). (To learn about the magnitude system go here.)
  • Color scheme” is a matter of personal preference. I prefer  “white on black background” for computer display. For printing you’ll use a lot less ink if you choose “black on white background.”
  • “Image size” I usually leave at 512 pixels. This really depends on your screen size. Try it. If too small and you have plenty of unused screen real estate, you can easily increase it.

That’s it. Just push the “update” button (between chart and form) and you will have a chart showing the bright stars – the ones that will put in an appearance about 45 minutes to an hour after sunset –  in the eastern sky for where you’re observing.

The Big Dipper is a familiar asterism within the constellation Ursa Major outlined here in a "Your Sky" chart.

The Big Dipper is a familiar asterism within the constellation Ursa Major outlined here in a "Your Sky" chart.

Can you do more with this? Yes – of course. For example, if you are looking for a bright asterism, check “Constellations: Outlines.” Most of the bright asterisms we use are part of a constellation and you can probably spot the asterism within the constellation outline. For example, the Big Dipper is a bright asterism that is part of the Constellation Ursa Major.

You can easily change the direction you are looking and brightness of stars visible.  My first concern is to give you a way to generate charts similar to the ones I use in the Prime Time Web site, but adjusted for your location.  Here are a few more suggestions. If you are in a heavily light-polluted area and you want to observe after it gets fully dark, you may still  want to restrict the brightness of stars to 4 to roughly match what you see.  In a rural area this can be set to 6 – the generally accepted limit for naked eye observing roughly 90 minutes after sunset when it is fully dark.

If you want a more elaborate star chart with many more details, I suggest you get one of the planetarium software programs and learn to use it. I use “Starry Nights Pro.” but this comes in several variations at different prices and for observing with naked eye and binoculars the simpler and less expensive versions are fine.

Many amateur observers I know prefer “The Sky” software.

And there is a new, free, planetarium program I’ve used a little called “Stellarium.” I really like its graphics, but I’m more comfortable with Starry Nights, a program I have used for years.

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

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

Sky and Telescope gives this example as a typical experience:

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

You can read the full Sky and Telescope report here.

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

Yikes! NASA captures a space monster!

NASA’ reports that it’s “Spitzer Space Telescope has imaged a wild creature of the dark — a coiled galaxy with an eye-like object at its center.The ‘eye’ at the center of the galaxy is actually a monstrous black hole .” The image is below – click on it for a larger version. (The rumor tha the ate Mars isn’t true – for the truth about Mars see this post!)

coiled_monster

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Step-by-step

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

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

Step 1

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

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

Step 2

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

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

Step 3

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

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

Step 4

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

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

Step 5

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

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

Step 6

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

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

Step 7

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

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

Step 8

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

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

Final Step

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

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

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

mw_finished

. . . and how to use it.

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

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

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

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

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

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

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

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

Galactic coordinate system

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

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

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

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

galactic_coordinates

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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