24 Sep 2006
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 thatâ€™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!
03 Sep 2006
Ah... it's back-to-school time. How about we have a friendly little astronomy quizzie to put us all back into School Mode? Those of you who read here regularly know that this is not a genuine quiz so there is no need for clammy hands and shortened breath. And there are only three true-or-false questions. So sit back and enjoy a little exercising of the grey cells.
1. Only a select few people on the planet can see an eclipse.
OK, admittedly that was sort of a trick question. I should specify lunar or solar eclipse. Few people see a solar eclipse in a lifetime; most everyone on the planet can see a lunar eclipse though. Why?
An eclipse is basically one body casting a shadow on another. If the Moon squeezes in between the sun and us, for example, it can cast a shadow somewhere on Earth. But it's just a pinprick of a shadow, sometimes only tens of miles across. And the shadow races across the surface of our planet at about 1000 miles per hour.
This is a solar eclipse, and it is an amazingly ethereal phenomenon to observe. But you have to be in the exact right place to be in "the umbra" or full shadow. To see one you will probably have to get up and go somewhere. If you are not content on actually traveling to see one, be patient, your area probably will get a total solar eclipse in the next three or four centuries.
A lunar eclipse is a different duck. When we cast a shadow on the Moon, it's no tiny pinprick. Our shadow can cover the entire Moon! The benefit of a lunar eclipse is that everyone on one side of the earth can see it. It's a free show from your own backyard. And if you miss one you only need wait another 6 months or a year to see it again. In the average lifetime one can see literally dozens of them.
2. Your date of birth determines which astrological sign you are.
This really is an astronomy-related statement! We are told that the moment of your birth determines what "sign" you are; whether you are Capricorn or Aquarius or Leo, etc. And your sign is determined by which constellation the sun is in at that special moment.
But the charts that are used to tell us what our sign is were made thousands of years ago. Here's the problem. Since that time our planet has wobbled ever so slightly in its spin position - not much, but enough to "shift" the constellations through the calendar a wee bit.
So, for example, on January 27 a few thousand years ago we would have found the Sun occupying the region in space dedicated to Aquarius. Since then, though, our wobble has shifted the January 27 sun into Capricorn.
Meaning, although the newspaper horoscope will peg a baby born then as an Aquarian, the sun was really in Capricorn at her birth. So what sign is she - Aquarius or Capricorn? Good question. And the same dilemma follows for nearly everyone reading this now: Nearly all of us are off by one sign. More than 90% of the people reading horoscopes have been reading the "wrong" sign. Hmmm...
3. Pluto is a planet.
This is an emotional subject as of late! Since its discovery in 1930, this little guy has been considered a planet. And why not? It was the next heavenly body discovered beyond Neptune; it should be a planet.
But wee Pluto has been trying to tell us something since those early days.
For one thing, it is a very, very small orb, smaller than our country let alone our Moon and a handful of other heavenly objects not considered planets. Its orbit is way wacky; it's outside the regular plane of the rest of the planets, and sometimes it's closer to the sun than Neptune.
And for the last ten years we've seen a whole truckload of other Pluto-like objects out in the deep areas of our solar system, beyond Neptune, seemingly filled with icy bodies of all sizes, one bigger than Pluto itself.
Which is why it was agreed by voting astronomers recently that maybe Pluto should just be considered the "first found" of those trans-Neptunian objects, aka Kuiper Belt Objects.
But the controversy isn't over. A small but vocal group of astronomers who want to keep poor Pluto as a proper planet is demanding a recount. So stay tuned, maybe we won't need to downsize the little guy - yet.
Get all three correct? If not, no worries. None of these statements were too black and white. That's the nature of science; lots of gray, a little black and white. Until next time, clear skies!