Star date: 11:23:98
Exploring the Winter SkyThe winter sky is the prettiest and most interesting time of year for amateur astronomers in the northern hemisphere. Despite the frezzing cold temperatures and numb fingers, astronomers both amateur and professional bring their telescopes into the cold night air. Why is this? Why take a chance on suffering frostbite for a few hours of observation?
There are many reasons. The winter sky offers us the constellation Orion, the Double Cluster in Perseus, the Andromeda Galaxy, the Geminid meteor shower and many other treats. In addition, this year also offers us the spectacular king of the planets, Jupiter, and the beauty of Saturn with it's magnificent set of rings.
This week we will begin to look at that mighty constellation, Orion the hunter. Of all the constellations visible in the northern hemisphere, Orion is probably the second most easily recognized of the constellations behind only the Big Dipper. Orion also contains two of the most famous stars, Betelguese and Rigel. The easiest way of finding Orion is to look for the belt of Orion. These are the only three stars in the sky which draw out a near perfect line within just a few degrees of each other. At about 10 pm at this time of year, Orion can be found in the southeast sky. Look for it about thirty degrees above the horizon.
Thirty degrees can easily be found by holding a fist vertically at arms length. The distance from your index finger to your pinkie will be covering about 10 degrees. Simply do this three times to find about 30 degrees. If you picture Orion facing us, his right shoulder is a bright red star. This is the red giant Betelgeuse. This is a star just slightly more massive than our Sun, yet larger than the orbit of the planet Mars.
Red giaints are older stars, which have already run out of their hydrogen fuel and are now burning helium. Stars are kept stable throughout most of their lives by the balance of nuclear fusion trying to push them outwards and the crushing force of gravitation trying to collapse the star. When the star runs out of it's hydrogen fuel, gravity begins pulling the star inwards. When the pressures inside the star become great enough, the helium (which is the ash from hydrogen fusion) begins to fuse. The star then quickly expands outwards, to a swollen parody of itself. The temperature of the surface then cools beacause the atoms in the surface are now further apart. This causes the surface to appear red. Thus, the term red giant.
One day in about 5 billion years, when our own Sun runs out of it's hydrogen fuel, it too will become a red giant. When it does this, our Sun will easily swallow the planets Mercury, Venus, and the Earth. It may even engulf Mars.
Looking at Orion with the same orientation that he is facing us, his left foot is another bright star, yet this one is blue. This is the star Rigel. Rigel is another type of star, known as a blue giant. Blue giants have little in common with red giants except they are both, well, giants. Unlike red giants, however, blue giants are massive stars containing between twenty and fifty times the mass of the Sun. Their crushing gravity means that there must be a tremendous amount of nuclear reactions occuring in the core in order to keep the star stable. They also have more fuel than a smaller star, so you may think that the two factors would cancel each other out, leaving each type of star with about the same lifetime. This turns out not to be the case. Giant stars like Rigel burn their greater reserves of fuel at a much greater rate than due smaller stars, and thus have much shorter lifetimes. A blue giant like Rigel may live only a few dozen million years before it's final collapse. Stars like this, though, can sometimes form that most exotic of astronomical objects, a black hole.
The belt of Orion contains a very beautiful nebula, M42. This is also called the Great Nebula in Orion. Look for it as the middle "star" in the sword of Orion. This is easily seen with any backyard telescope or binoculars. Also just above the belt of Orion (on his "right" or eastern side) is the reflection nebula M78. This is a magnitude 8 nebula, streching about 1/7 of a degree across the sky.
Clear skies, and good viewing.
