[ FirstLight Astronomy Club ] The Skies Above

« June 2003 | Main | August 2003 »

Got Milk?

The Galaxy >

This week is a perfect week to go outside in the later evening and have a Milky Way. Few laymen really have a grasp of what that famous big band of starry light is and our place in it. Let's investigate.

First imagine a disk, very thin compared to its breadth, like a CD. The galaxy we live in is like this; but a thin disk over 100 thousand light years across made up of over 100 billion stars.

There are actually stars all over the disk, but it's called a spiral galaxy because the bigger, brighter, show-off stars are located in what are called spiral arms, in effect lighting the arms up. A distant observer would see our galaxy as something resembling a flattened pinwheel of countless tiny lights. Our sun is nestled inside that disk, about two-thirds of the way out.

Now move your imaginative self into that disk. Looking around you see that the giant spiral now appears as a flat plane of stars surrounding you. It is this line of light that most of us know as the Milky Way, that band of stars painted over our heads during the summer nights.

But what about the stars which are not in the Great Band? Those stars all around us, even those nowhere near the band of light, are part of our Milky Way, too.

Our sun, Polaris, the stars of the Big Dipper and Orion are all part of the Galaxy. These thousands of visible stars are just close neighbors, above and below our position in the enormous spiral.

Bottom line? Everything you can see with your naked eye is part of our Galaxy, the Milky Way.

Then if there are over 100 billion stars why can we only see 1000's of them? You're sitting on the answer. The very stuff of you and the chair and your dog and the Earth is spread out all over the disk as fine microscopic dust. We live in a filthy galaxy. You can get glimpses of this dust as you look out at the Milky Way from a very dark place on a clear, Moonless night. Here's how.

Slowly moving your eyes from north to south along the Milky Way you'll notice discontinuities in the band of light. These dark blotches are the especially dusty areas in the disk.

But this crud is a good and wonderful part of the make-up of our special galaxy. That dust, created in stars and scattered about over the eons, can be used to make planets and dogs and you.

One recent insight into our position in the Milky Way is worth noting.

Our sun moves around the galaxy like a planet around a star. The whole grand tour lasts over 200 million years and takes our solar system in and out of the great spiral arms. At the moment we are off a spiral arm, which is actually a great place to be. Why?

Being inside a spiral arm it's dusty, and it would be hard to enjoy the entire rest of the universe. Imagine all the great telescopes, from Palomar to the Kecks to Hubble, trying to observe the great mysteries of creation from inside a dusty arm. Not a pretty thought.

Being off an arm opens up the skies like coming out of a fog. From our present position we can see millions of other galaxies and supernovae and gamma ray bursters and so on and so on.

One of the great "coincidences of life" puts us in the perfect seat at the perfect time for using the best instruments to study the magnificent wonders of the universe.

Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.

Posted by Administrator at 2003.07.19 01:20 PM | Comments (0)

Thuban: Ye Olde Northe Starre

The Galaxy >

There is a special star in the sky which, in days of old, had a place of great prominence. Great civilizations revered it. Monuments were built by its position in the heavens. Alas! Nowadays it is nothing but an average member of the congregation of starry hosts, hardly discernible from the thousands of other stars in the night sky.

This star is Thuban. It can be found, but not easily, in the northern skies surrounded by its more renowned neighbors. Go outside tonight and do this: Find the North Star, Polaris. It is --- obviously --- due north and about two hand spans (held at arm's length) above the horizon. It is essentially by itself so it isn't too difficult to pick out.

Now find the Dipper. Using both Polaris and the stars at the end of the handle of the Dipper as your "end stars," can you find the two stars right between them? They are relatively easy to pick out and, for the sake of trivia, are part of the bowl of the Little Dipper.

Now you need to set your night vision to "sensitive." Right between these two stars and the stars at the handle of the Big Dipper is a dim star. That is Thuban. (A helpful star map can be found here.)

For the science-minded reader, Thuban is actually a tremendously big, very bright star. It is an A-class star (translation: hot and bleeding energy profusely) but it is a good distance away, over 300 light years. That explains its relative dimness.

So how is it that a dim, insignificant A-class star was once an A-list star to the ancients?

In days of old, nearly 4600 years ago, Thuban --- not Polaris --- was the North Star! All the constellations of the northern skies traversed around it.

About that time, the eminent empire of the Egyptians was erecting the great pyramids. All indications are that a pyramid built at that time was architecturally lined up with Thuban, the then-North Star.

Going down Pyramidal passageways, many of which were lined up in a north-south direction, one could look down the hall and see Thuban sparkling outside all night.

So how is it that Thuban was pushed from this limelight? Precession!

The earth spins like a top, with the top of our top always pointing in the same direction. Well ... not always. It just appears that way. During your lifetime our planet will spin around thousands of times, all that time with its axis seeming to point at that same star, our North Star, Polaris.

But like a top that is slowing, our planet wobbles about while spinning. This wobble is called precession. And although we can see the wobble in a spinning top after just after a few tens of spins, our planet takes 26000 years worth of spinning to wobble around just once!

Now imagine a spinning top with a laser light beaming out the top of it --- along its "axis of rotation."

Precession would cause the lightbeam to slowly draw out a circle on your ceiling. Earth does something similar, only without the laser light, of course. In the four-and-a-half millennia since Thuban reigned as North Star, the "point" directly above our spinning planet has circled over and around to Polaris, our current North Star.

Where is this point above our axis headed for now? See if you can find that bright star almost directly above our heads tonight. That is Vega, a bright blue hot star just 25 light years away. Stick around until about A.D. 14000 and you'll be able to use Vega as your wayfinding North Star.

Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.

Posted by Administrator at 2003.07. 5 01:23 PM | Comments (0)



Looking for something?	« June 2003 \| Main \| August 2003 » Got Milk? The Galaxy > This week is a perfect week to go outside in the later evening and have a Milky Way. Few laymen really have a grasp of what that famous big band of starry light is and our place in it. Let's investigate. First imagine a disk, very thin compared to its breadth, like a CD. The galaxy we live in is like this; but a thin disk over 100 thousand light years across made up of over 100 billion stars. There are actually stars all over the disk, but it's called a spiral galaxy because the bigger, brighter, show-off stars are located in what are called spiral arms, in effect lighting the arms up. A distant observer would see our galaxy as something resembling a flattened pinwheel of countless tiny lights. Our sun is nestled inside that disk, about two-thirds of the way out. Now move your imaginative self into that disk. Looking around you see that the giant spiral now appears as a flat plane of stars surrounding you. It is this line of light that most of us know as the Milky Way, that band of stars painted over our heads during the summer nights. But what about the stars which are not in the Great Band? Those stars all around us, even those nowhere near the band of light, are part of our Milky Way, too. Our sun, Polaris, the stars of the Big Dipper and Orion are all part of the Galaxy. These thousands of visible stars are just close neighbors, above and below our position in the enormous spiral. Bottom line? Everything you can see with your naked eye is part of our Galaxy, the Milky Way. Then if there are over 100 billion stars why can we only see 1000's of them? You're sitting on the answer. The very stuff of you and the chair and your dog and the Earth is spread out all over the disk as fine microscopic dust. We live in a filthy galaxy. You can get glimpses of this dust as you look out at the Milky Way from a very dark place on a clear, Moonless night. Here's how. Slowly moving your eyes from north to south along the Milky Way you'll notice discontinuities in the band of light. These dark blotches are the especially dusty areas in the disk. But this crud is a good and wonderful part of the make-up of our special galaxy. That dust, created in stars and scattered about over the eons, can be used to make planets and dogs and you. One recent insight into our position in the Milky Way is worth noting. Our sun moves around the galaxy like a planet around a star. The whole grand tour lasts over 200 million years and takes our solar system in and out of the great spiral arms. At the moment we are off a spiral arm, which is actually a great place to be. Why? Being inside a spiral arm it's dusty, and it would be hard to enjoy the entire rest of the universe. Imagine all the great telescopes, from Palomar to the Kecks to Hubble, trying to observe the great mysteries of creation from inside a dusty arm. Not a pretty thought. Being off an arm opens up the skies like coming out of a fog. From our present position we can see millions of other galaxies and supernovae and gamma ray bursters and so on and so on. One of the great "coincidences of life" puts us in the perfect seat at the perfect time for using the best instruments to study the magnificent wonders of the universe. Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com. Posted by Administrator at 2003.07.19 01:20 PM \| Comments (0) Thuban: Ye Olde Northe Starre The Galaxy > There is a special star in the sky which, in days of old, had a place of great prominence. Great civilizations revered it. Monuments were built by its position in the heavens. Alas! Nowadays it is nothing but an average member of the congregation of starry hosts, hardly discernible from the thousands of other stars in the night sky. This star is Thuban. It can be found, but not easily, in the northern skies surrounded by its more renowned neighbors. Go outside tonight and do this: Find the North Star, Polaris. It is --- obviously --- due north and about two hand spans (held at arm's length) above the horizon. It is essentially by itself so it isn't too difficult to pick out. Now find the Dipper. Using both Polaris and the stars at the end of the handle of the Dipper as your "end stars," can you find the two stars right between them? They are relatively easy to pick out and, for the sake of trivia, are part of the bowl of the Little Dipper. Now you need to set your night vision to "sensitive." Right between these two stars and the stars at the handle of the Big Dipper is a dim star. That is Thuban. (A helpful star map can be found here.) For the science-minded reader, Thuban is actually a tremendously big, very bright star. It is an A-class star (translation: hot and bleeding energy profusely) but it is a good distance away, over 300 light years. That explains its relative dimness. So how is it that a dim, insignificant A-class star was once an A-list star to the ancients? In days of old, nearly 4600 years ago, Thuban --- not Polaris --- was the North Star! All the constellations of the northern skies traversed around it. About that time, the eminent empire of the Egyptians was erecting the great pyramids. All indications are that a pyramid built at that time was architecturally lined up with Thuban, the then-North Star. Going down Pyramidal passageways, many of which were lined up in a north-south direction, one could look down the hall and see Thuban sparkling outside all night. So how is it that Thuban was pushed from this limelight? Precession! The earth spins like a top, with the top of our top always pointing in the same direction. Well ... not always. It just appears that way. During your lifetime our planet will spin around thousands of times, all that time with its axis seeming to point at that same star, our North Star, Polaris. But like a top that is slowing, our planet wobbles about while spinning. This wobble is called precession. And although we can see the wobble in a spinning top after just after a few tens of spins, our planet takes 26000 years worth of spinning to wobble around just once! Now imagine a spinning top with a laser light beaming out the top of it --- along its "axis of rotation." Precession would cause the lightbeam to slowly draw out a circle on your ceiling. Earth does something similar, only without the laser light, of course. In the four-and-a-half millennia since Thuban reigned as North Star, the "point" directly above our spinning planet has circled over and around to Polaris, our current North Star. Where is this point above our axis headed for now? See if you can find that bright star almost directly above our heads tonight. That is Vega, a bright blue hot star just 25 light years away. Stick around until about A.D. 14000 and you'll be able to use Vega as your wayfinding North Star. Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com. Posted by Administrator at 2003.07. 5 01:23 PM \| Comments (0)
	Powered by Movable Type 3.14