ASTR 101 Lecture 2: Size and Scale
Document Summary
Earth is 15,000 km wide while the sun is 1,500,000 km wide. Live stars can be as small as 1/10 of the sun, but can be as large as 1000x of the sun. Sun will eventually become a white dwarf, which is about the size of the earth. The galaxy is about 100,000 light years across. A light year (ly) is the distance light travels in one year. Distance = velocity x time (vt=d; d/t=v; d/v=t) 1 light year = c x 1 year = 1013 km c = 300,000 km/s = 3 x 105 km/s = 3 x 108 m/s. 1 year = x 107 seconds: distance = 1ly, speed = c, time = 1 yr. 1 ly = (3 x 105 km/s) x ( x 107 s) = 10 trillion km. The nearest star system is alpha centari. Space between stars is too huge to have star collisions.
