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Strolling Down the Late Summer Milky Way
Observing >
Let's take a late summer stroll down the lane, that cloudy lane of stars bisecting the night sky - the Milky Way.
This week is a good week to do so, weather and light pollution permitting. The Moon is below horizon until the wee hours of the morning and won't blot the sky with its intense brightness.
The Milky Way is easy to find, assuming you are not near an auto mall or casino whose lights turn night to day. It is the faint band of light stretching from the southern horizon across almost directly overhead and into the north.
It is of course our home galaxy seen edge on. We live in the disk of this collection of hundreds of billions of star and can see it all year long. But the summer Milky Way is especially easy to see because at this time of the year our night sky faces the more densely populated center of the galaxy. Our winter sky faces the dimmer suburbs of the galaxy.
The southern sky is a fine place to start our skywalk. (You can customize your own star chart at skytonight.com to follow along visually.) It is in the southern skies where the Way is brightest, in the constellation of Sagittarius. And in that teapot-shaped constellation resides the center of our galaxy. You can't see the billions of stars there, let alone the supermassive blackhole eating away at the very center, because of all the dust. But it’s there... trust me.
Scan around the top of the teapot with binoculars or a telescope and you should be able to spot several star clusters and faint nebulae. These are star birth regions similar to the Pleiades and the Orion Nebula.
Follow the Milky Way up into the sky, about two-thirds of the way up. There is a bright star called Altair in the constellation Aquila. Altair is unique in that it spins once on its axis every 6 hours or so. Compare that to our sun, which takes nearly a month to do so and you can see we have ourselves here one speedy spinner. It spins so fast that it is actually about 14% wider at the equator than at its poles.
Nearly above your head, can you see the cross-shaped constellation of Cygnus the Swan? At the "top" of the cross is Deneb, a bright star that pours out more energy in one day than the sun does in 140 years. Take Deneb, Altair and that bright star almost directly above your head, Vega, and you've got yourself the Summer Triangle.
At the foot of the cross await two stars - yes, two. It appears as just one with the naked eye, but that’s only because our eyes cannot resolve them - they are that close. They are Albireo, a binary star system about 380 light years away. If you have access to a scope take a look at them. They are a colorful pair; one is a pinkish-orange, the other a bluish-white.
At the intersection of the cross you might be able to spot another open cluster of stars with the poetic name of M29. Only 4000 light years away the cluster should be brighter than it appears. Then why so dim? For the same reason we can't see the galactic center; objects in the Milky Way disk lose a lot of their light to the massive clouds of dust there.
Follow the path now until you reach familiar Cassiopeia, the Queen, residing in her big zig-zaggy throne in the sky. Need some pure trivia? Travel to Alpha Centauri, one of the closest stars to earth just over 4 light years away, look back home, and you will see our sun as one of the stars in Cassiopeia. Don't laugh! That may win you a lot of money some day on Jeopardy.
Is there more to the Milky Way than this? You bet. This was just an attempt to get you outside and take a wondering look upwards. With a scope or even binoculars you can see all kinds of star clusters and nebulae, single stars and doubles.
Now go, and take a walk through the Way. Until next time, clear skies!
Posted by Mark Ritter at 2006.09.24 10:11 PM | Comments (0)
