10 Stellar Facts for Astronomy Buffs

Astronomy holds a lifetime of fascination for observers of the heavens. Astronomer and author Jay Pasachoff shares ten stellar facts of interest to amateur astronomers and scientists alike.

1. Jupiter, Saturn, Uranus, and Neptune all have rings.

2. The Sun is middle-aged; it's halfway through its 10-billion-year lifetime.

3. Astronomers think that all of the normal matter in the universe makes up only about 5 percent of the contents of the universe. Dark matter is thought to make up about 25 percent, and a strange form of energy known as the cosmological constant is thought to make up the remaining 70 percent.

4. As a result of the greenhouse effect, Earth's average temperature is comfortable rather than freezing, and Venus is a horrid place, hot enough to melt lead.

5. Pulsars are dead stars that have collapsed. Some spin around in as little as 1/500 second, pretty fast for a body that contains as much mass as the Sun.

6. The Sun--as big as it seems to those of us on Earth--is actually on the small side for a star. It's a dwarf star; giants and supergiants are much larger, and neutron stars are even smaller.

7. Earth's galaxy, the Milky Way, contains about 400 billion stars. That's not all: There are hundreds of billions of other galaxies in the universe, some of which are much larger and contain many more stars than the Milky Way.

8. Wherever you are in the universe, distant clusters of galaxies seem to move away from you. The farther away they are, the faster they recede. This leads many astronomers to believe that the universe is expanding.

9. Astronomers have discovered dozens of planets orbiting stars other than the Sun. We know of many more planets outside our solar system than inside.

10. Explosions on the Sun send particles into space, creating luminous displays called auroras that can be seen from Earth.

Learn more about stars, planets, and the rest of the universe in Encarta Encyclopedia's article on Astronomy.

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Jay M. Pasachoff, A.B., A.M., Ph.D., is Field Memorial Professor of Astronomy and Director of the Hopkins Observatory at Williams College in Williamstown, Massachusetts.

Dr. Pasachoff has a great talent for teaching people about astronomy. Hundreds of thousands of amateur astronomers own well-thumbed copies of his Peterson Field Guide to the Stars and Planets, and his Astronomy: From the Earth to the Universe is a standard college astronomy textbook. He specializes in the study of the Sun during total eclipses, the formation of the elements in the early universe, the planets of the solar system, and observational cosmology. He has traveled all over the world in order to observe eclipses from prime viewing locations.