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

Whats Up in the Sky September, 2006 (Extra)

How Celestial Objects Are Named

Amid all the Pluto is no longer a planet hubbub, some friends recently asked me about how things like planets and stars get named. After a brief explanation with a couple of examples, I became intrigued by some of the more subtle details in this story.

The Sun, Moon, and visible planets (Mercury, Venus, Mars, Jupiter and Saturn) were all named by the ancients who believed them to be mythological gods. The astronomers who first identified Uranus, Neptune, and Pluto continued that tradition. Constellations such as Hercules, Perseus, and Andromeda also take their names from ancient mythology, although several visible only in the southern hemisphere have names like Antila (the Air Pump) and Telescopium because they were named by European explorers who first sailed southern seas.

Other categories of objects follow different rules of naming. Satellites of planets go through a process where they first receive a number indicating the year of discovery, then are assigned a Roman numeral, and then may receive a name from mythology. So when Voyager 2 found a bunch of new moons around Neptune in 1989 they were first designated, for example, S/1989 N 1 which later became Neptune VIII and finally Proteus. The moons of Uranus are the exception to the mythology rule – they are named by their discoverers after characters from the writings of Shakespeare and Pope such as Caliban and Puck.

Asteroids are also given a provisional number at first, but when their orbits are understood well enough for us to be able to predict their positions, they receive a permanent number and name. Therefore, 253 Mathilde is the 253rd asteroid to be numbered but not necessarily the 253rd to be discovered. Asteroid discoverers are afforded much more latitude in their choice of names. Asteroids can be named for almost anything so we have 2309 Mr. Spock, 3834 Zappafrank and 8749 Beatles.

Comets are generally named for the person or persons (up to three) who first discover them. Comet Halley is probably the most familiar example, named after famed English scientist and astronomer Edmund Halley. He was not the first to observe the comet, records of its appearance date back to ancient China, but he was the first to understand its nature and predict its return. More recent examples include comets Hale-Bopp, Hyakutake and Shoemaker-Levy 9 (the 9th one found by Carolyn and Gene Shoemaker and David Levy).

Surface features like craters or mountains on asteroids, planets, or moons follow complicated rules set by the International Astronomical Union Nomenclature Committee. Basically they are named after noteworthy places, things, or individuals who are no longer be living nor political or religious figures from the last 200 years. Examples include lunar craters Tycho, Copernicus, and Scobee; valleys on Mercury such as Arecibo and Goldstone (named after radio telescopes); and the Amsterdam crater on Mars. These features also take their names from the places and stories of Norse, Chinese, Japanese, Indian, Hawaiian, Native American and Aboriginal mythology.

There is one group of objects that no longer receive names other than catalogue numbers: the stars. The brightest stars, like Sirius or Betelgeuse, retain their names from antiquity, but astronomers use several systems for naming stars so Sirius is also known as Alpha Canis Majoris, 9 Canis Majoris, HR 2491, HD 48915, BD-16 1591 and the Dog Star. Stars, however, cannot be officially named after you, nor can you buy a star. Those names exist only in the book the company sells you.

Its all in the name and its all up in the sky.

Peter Burkey – SAAA President