Chapter 1 The Scale of the Cosmos

Chapter 1 Essential Questions 1) Where is Earth in relation to the sun, the planets an the galaxy? 2) How do astronomers talk about these huge astronomical distances? 3) Which objects are big, which are small? 4) Are there other worlds like Earth?

1) Where is Earth in relation to the sun, the planets an the galaxy? Earth is a planet found in our solar system, consisting of the sun, planets and smaller bodies such as moons and comets. 3rd rock from the sun, 1 AU (astronomical unit: distance from Earth to the sun) from the sun Our solar system is about two-thirds of the way from the center of our galaxy Planets: small, non-luminous bodies that shine by reflected light Star: self-luminous ball of hot gas that generates its own energy.

2) How do astronomers talk about these huge astronomical distances? Astronomical units (AU): distance from the middle of Earth to the middle of the sun- used to talk about distances in our solar system Light year (ly): the distance that light travels in one year. Roughly 1013km or 63,000 AU- used to talk about the distances of stars in our galaxy The nearest star to our sun is Alpha Centauri- 4.2 ly from Earth Parsec and Mega Parsec- this is to measure distances outside of our galaxy- this will come up in later chapters

3) Which objects are big, which are small? Small-comets, moons, planets, stars, solar systems Large Galaxy: a great cloud of stars, gas and dust bound together by the combined gravity of all the matter-range from 1500-300,000 ly in diameter Cluster: group of galaxies Super cluster: clusters of clusters

4) Are there other worlds like Earth?