Whats Up in the Sky October, 2006
The Andromeda Galaxy
One of the best parts of teaching astronomy occurs when students observe really cool stuff for the first time. Craters on the Moon, Saturns rings and the moons of Jupiter are always favorites, but whenever I had students out at this time of year, I made sure we observed M31, the Andromeda Galaxy.
Currently, the Andromeda Galaxy is conveniently located high in the eastern sky. To find it, go out an hour or two after sunset to a dark location, away from city lights, face east and look for the Great Square of Pegasus, four stars in the shape of a square standing on one corner. Its large – as wide as two fists held at arms length – and over halfway between the horizon and overhead. Starting at the left-hand corner, count over two stars to the left and then two stars up and look for a small, fuzzy patch of light. To aid your efforts, I recommend you use a star chart such as those found in Astronomy or Sky and Telescope magazines. Charts can also be found online. Simply go online and type the following URL, “http://www.mmsd.org/planetarium”.
There are a number of things which make this object unique. For most people, it is the only naked-eye object that is not part of our own Milky Way galaxy, making it by far the most distant object visible without a telescope. It is about 2.5 million light years away, so when you observe it your eyes are responding to some very old photons of light since they’ve been traveling through space for 2.5 million years.
Galaxies like M31 can be thought of as giant rotating pinwheels of several hundred billion stars. Our own Milky Way galaxy is a spiral about 100,000 light years across. Put two paper plates on either side of the living room and you get a rough idea of the relative size and separation of these two. They are members of the Local Group of about 20 nearby galaxies.
The Andromeda Galaxy has been observed since 905 A.D. and was on Persian star charts as the Little Cloud long before the invention of the telescope.
It was in M31 that Edwin Hubble, in 1923, discovered a certain type of star, called a Cepheid variable, which enabled him to determine its distance. This revolutionized how astronomers view the universe and was the beginning of modern cosmology.
Andromeda may play a large role in the future of our own galaxy as the two are approaching each other at roughly 120 km (75 mi.) per second. That means in about 3 billion years, there will be a collision of galactic proportions. Actually, individual stars will not collide but rather the galaxies will pass right through each other, both becoming deformed by the others gravity. A few million years before that, imagine how cool it will look, quite large up in the sky.
This month in history:
Oct. 1: Yerkes Observatory dedicates 40 inch refractor – 1897
Oct. 1: NASA founded – 1958
Oct. 4: Space begins with launch of Sputnik 1 – 1957
Oct. 5: E. Hubble discovers variable stars in M31 – 1923
Oct. 12: First 3-person space mission, Voskhod 1, launched – 1964
Oct. 14: Chuck Yeager breaks sound barrier – 1947
Oct. 22: First record of solar eclipse – 2136 BC
Oct. 24: Final flight of X-15 rocket plane – 1968
Oct. 30: First launch of Saturn rocket – 1961
Here are this months viewing highlights:
Planets this month: Most of the planets are not easily visible this month, the exception being Saturn, which can be found in the southeast before sunrise.
Oct. 6: Full Moon
Oct. 9-10: Gibbous Moon occults Pleiades
Oct. 13: Last-quarter Moon.
Oct. 20: Orionid meteors peak.
Oct. 22: New Moon.
Oct. 24: Use binoculars to see Moon, Jupiter, and Mercury on SW horizon 35 min. after sunset.
Oct. 29: First quarter Moon.
Peter Burkey – SAAA President