Dr. Ken Rumstay's SPIRAL CORNER

OBSERVER'S NOTEBOOK

Greetings all!

Winter 2006 officially began on December 21st at 7:23 pm EST in the U.S. I love to stargaze this time of year; it seems as though the winter evening sky has more than its share of bright stars.


Image: courtesy Roger Smith/NOAO/AURA/NSF

Orion, the most prominent constellation in the sky is high in the southeast. Look for three fairly bright stars in a straight line; this is the belt of mighty Orion! Every primitive culture has imagined a human figure in this pattern of stars, and Orion is usually portrayed as a warrior or a hunter. I prefer the latter.

Surrounding the three stars of Orion’s belt is a large rectangle formed by four stars, two of them exceptionally bright. At the upper-left corner is Betelgeuse, an orange supergiant star located some 520 light years from Earth. Most of our star names are of Arabic origin, though some are Greek and others Latin, and the names usually have some meaning. Translated from the Arabic, Betelgeuse means “armpit of the giant,” and in artistic renderings of Orion, this star is invariably located at the base of his right arm. Some things are better left untranslated!

Betelgeuse (at left) is the tenth brightest star in the sky, while Rigel in Orion’s left leg, is number seven. These two stars make a remarkable contrast. Both are tens of thousands of times more luminous than our own Sun, but for somewhat different reasons.

Image: HST/NASA

Rigel’s tremendous power output results largely from its high surface temperature; this blue-white star is twice as hot as our Sun, and about fifty times larger in diameter. Orange Betelgeuse is cooler than our Sun, but its huge size more than compensates for this. In fact, if Betelgeuse were transposed into the center of our solar system, this orange supergiant, with a diameter 700 times that of the Sun, would stretch more than halfway to Jupiter!

Orion contains numerous fainter stars, of course, and a chart will help you pick out his sword and shield. By picturing Orion as a hunter, we can construct a little tableau around him using the surrounding stars. A hunter has to have hunting dogs, right? And Orion has two. Below Orion and to his left lies the “Dog Star” Sirius, the very brightest star in our night sky. This star is not nearly as luminous as Betelgeuse or Rigel, but it is much closer to us, and lies only nine light years away. To visualize Canis Major (the greater dog), picture Sirius in its head. Below Sirius lies a triangle of three faint stars; remember, the dog is standing on his hind legs, but with one paw thrust towards Orion’s feet.

Sirius (left) in images taken by the Chandra X-ray Observatory, clearly shows its white dwarf companion. A white dwarf is a hyperdense star of compacted atomic matter that manifests itself when certain normal hydrogen-burning stars exhaust their thermonuclear fuel.

Image: NASA/CXC/SAO

The lesser dog, Canis Minor, requires a stretch of the imagination. Above and to the left of Sirius lies the bright star of Procyon. It is in fact the eighth brightest star, falling between Rigel and Betelgeuse. Like Sirius, its brightness stems from its proximity, only eleven light years away. Canis Minor is a long, skinny dog (a dachshund?) composed of just two stars: Procyon and Gomeisa.

Now, what prey is Orion hunting? Above Orion, and a bit to the right, is another bright orange star. Aldebaran, the eye of Taurus the Bull, ranks number thirteen in our list of brightest stars. Located 65 light years away, it is slightly hotter than Betelgeuse, but not nearly so large (“only” 25 times the Sun’s diameter!).

Aldebaran lies at one corner of a “V” of faint stars; these form the Hyades, the star cluster closest to Earth. Above Aldebaran lies a more distant, but much more familiar cluster, the Pleiades. Look for a group of five or six faint stars, forming a tiny box with a handle about the size of the of the Full Moon. Many people mistake this for the Little Dipper, but that recognizable collection of stars is much larger, and is always found in the northern sky. In Arabic, Aldebaran means “the follower”: for as the Earth turns Aldebaran follows the Pleiades as they move from east to west.

Finally, to the left of Procyon and slightly above it is the constellation Gemini, the twin brothers of ancient mythology watching the hunt. Look for two bright stars close together. The upper star is Castor; his twin Pollux lies just below.

If you own a telescope or a pair of binoculars, there are two easily-observed objects to look for in the winter sky. The first is of course the Pleiades (at left) in Taurus.




Easily visible to the naked eye, a telescope reveals more than a hundred stars in this fine cluster. The second is the Great Nebula in Orion.
Image: NASA

Below the central star of his belt (at about half the distance to Rigel) appears a tight grouping of faint stars; this is Orion’s sword. If you have sharp eyesight, you will notice that one of the stars looks slightly fuzzy. The telescope reveals the Trapezium, a tiny cluster of four bright stars, surrounded by the faint wispy material of the nebula itself. The stars in the Trapezium are among the hottest stars known! They emit prodigious amounts of ultraviolet light that causes the surrounding interstellar gas to light up like a neon sign. Nebulae such as these are stellar nurseries; thousands of newborn stars lie deep inside.

It’s worth emphasizing that even a small telescope or binoculars will reveal thousands of deep-sky objects. And even more important than the size of your telescope is the darkness and clarity of your sky. If you are considering purchasing a telescope, you might want to resist the urge to purchase the biggest one you can afford, and simply drive out of town with a smaller, more portable instrument.

But if you already have a telescope, look for a bright yellow orb rising in the east after Gemini. That’s the planet Saturn, and its beautiful system of rings makes it one of the finest of astronomical sights!

Dr. Ken Rumstay's SPIRAL CORNER

OBSERVER'S NOTEBOOK

A century ago, the Milky Way would have been familiar to all but the few who lived in the largest cities.

Most Americans of the era would have been able to point out at least a dozen constellations.



Today, a plethora of electronic diversions --- including the internet --- keep us indoors at night. For those who do venture outdoors, light pollution has washed the Milky Way out of most of our skies.

The end result is that few people today have the time or inclination to study the night sky. Yet stargazing is still loved by a hardy minority of millions!

To share in the fun, there’s no need to spend thousands on fancy equipment; in fact, there’s no need for equipment at all.

In my astronomy classes here at Valdosta State University, I always have my students observe the heavens for at least a week before hauling out the telescopes.

This column will provide tips on how to get the most out of your night sky. All that’s required are two good eyes and a clear sky.

The first thing you’ll notice about the night sky is that it’s dark! That seems obvious. But as Heinrich Olbers pointed out in 1823, this actually tells us a lot about our universe.

Without much evidence to the contrary, 18th century astronomers and philosophers believed that the universe in which we live was infinite, and had always existed.

In other words, the universe had no boundaries in space or time but Olbers pointed out that if this were true, then the universe would contain an infinite number of stars, and in whatever direction we chanced to look, our line of sight would eventually intersect the surface of one of those stars.

If so, then the entire sky would glow as brightly as the surface of the sun! This is obviously not the case, and cosmologists have since validated the theory of the big bang in which the universe had a definite beginning, forming some 14 billion years ago.

Because of Olbers’ Paradox, you’ll notice how dark everything really seems once you’re outside under a night time sky. Gradually as your eyes adjust and begin to dilate, you will notice gradations in brightness until your eyes are able to discern darkness.

Astronomers refer to this process as “becoming dark adapted,” which takes about five minutes for a typical adult.

Once you’ve learned the lessons of taking the time to allow your eyes to fully adjust to the night sky, then believe it or not, if you’re still not convinced that you can observe the cosmos without a piece of astronomical equipment, then the first thing to buy would be a small flashlight.

Buy one small enough to hold in your mouth. That may sound crazy or even unsanitary, but it’s a skill that you will find handy later on.

The lens of your new flashlight should be covered with some red translucent material. Since red light tends not to overpower human night vision like light from other parts of the spectrum, both amateur and professional astronomers use it to avoid killing themselves in the dark and to avoid diminishing their “dark adapted” night vision.

Plastic report binders from office supply stores typically sell translucent red covers that can be fashioned at the end of one’s flashlight. If that’s too hard to track down, then red cellophane or even painted-on red nail polish applied to the flashlight lens can do the trick.

In some cases, the head of the flashlight can be disassembled to allow the filter to be placed against the inner surface of the lens. If not, simply secure it into place with double-sided adhesive tape.

If observing near your own house, turn off all your outside lights and if you can convince the neighbors to join you, have them do the same. Leave the house, and use your newly fashioned red light flashlight to make your way to a spot clear of obstructions from nearby trees or buildings.

Turn off your red light, wait five minutes or so, and look upwards. Towards the north, you should be able to see the Big Dipper, the most famous and most easily recognized set of stars within any of the constellations.

Depending on the date and the time of night, the Dig Dipper may be rightside-up, upside-down, or standing on its handle. But it is always in the northern sky. In November and December it is rightside-up. But at its lowest point; if you live in the southern United States, it may be obscured by trees or buildings.

Higher in the northern sky, you will see five stars, easily visible but not terribly bright, which form a shape not unlike the letter “M.” That’s the constellation of Cassiopeia, the Queen of Ethiopia, seated on her throne.

Now turn towards the west. High in the sky are three bright stars which form the so-called “Summer Triangle.” The Summer Triangle is not a constellation. Its three stars are each the brightest stars in three separate constellations.

The star at the top of the triangle is Deneb; hanging down from it (and tilted at a slight angle to the left) are stars which form the shape of a cross. This is the constellation of Cygnus the swan, although the pattern is also commonly known as the Northern Cross.

Below Deneb is a much brighter star called Vega. Vega belongs to the constellation of Lyra the harp; the other stars in Lyra form a parallelogram to the left and slightly above Vega itself. These stars are faint; you may have difficulty seeing them if your sky is not very dark.

To the left of Vega, is the bright star Altair. Altair belongs to the constellation Aquila, the eagle. But it in now way resembles an eagle! At least I’ve never seen an eagle in it.

Next time, we’ll look at some of the constellations rising in the east at this time of the year. There are many myths and legends immortalized in the night sky, and they are accessible to everyone!

Image: courtesy Roger Smith/NOAO/AURA/NSF