The Light Year The distance light travels in

The Light Year • The distance light travels in one year. • How far is it? • 1 lyr = (speed of light) x (1 year) • 1 lyr = (3 x 108 m/s) x (365 * 86400 s) • 1 lyr = 9. 4 x 1015 m, or about 1016 m.

The furthest man made object? • Voyager 1, at 1013 m away. • It has only traveled one-thousandth of a light year in 35 years!

Planets and Asteroids • Planets: Clumps of rock or gas held together by gravity. • Asteroids: Space Rocks Asteroid Gas Giant Terrestrial Planet

Distance between planets: about 1 light-hour

Stars • Balls of gas compressed by gravity until nuclear fusion occurs, releasing energy and halting the collapse. • Nuclear fusion is the main job of the star: creating elements by fusing atoms together • Our sun is an average star. • Stars make up the majority of the mass in any stellar system (99. 9%) • Most stars are not singlets.

Stellar Classification • Classic mnemonic: “Oh, be a fine girl, kiss me. ” • Comment on temperature, color, size • Our star is classified as G

Stars have an average separation of about 10 lyr

Nebulae • Interstellar gas that has not collapsed into stars yet. • 10 -100 lyr across • Referred to as “Stellar Nurseries”

The “Pillars of Creation” 7 lyr

Crab Nebula This used to be a star. What you’re looking at is the aftermath of its supernova.

Reflection Nebulae A collection of gas and dust that cannot yet create its own light but can reflect the light from nearby stars.

Planetary Nebulae Hot gas sprayed out by a star

Galaxies • Collections of Stars bound gravitationally. Usually held together by a supermassive black hole • Our galaxy is the Milky Way. • About 100, 000 lyr across • They contain about 1011 or 100 billion stars.

Distance between Galaxies: Millions of lyr