ASTR 100 Lecture Notes - Lecture 3: Cosmic Calendar, Milky Way, Scientific Method

• School: University of Maryland
• Department: Astronomy
• Course: ASTR 100
• Professor: Sylvain Veilleux

Document Summary

First, we will need to talk about scientific notation. This is the notation used by scientists to express really small or really large numbers that cannot be easily expressed in decimal form. We move the decimal point 6 places to the left and get 0. 000001. 1 g cm 3 is the density of water. 5. 5 g cm 3 is the average density of earth. 01 29 cm 3 is the average density of the universe. Defined as the distance light can travel in a year. Around 11 trillion kilometers of 6 trillion miles. The astronomical unit is the distance from the earth to the sun or. One light year is around 63,000 au. From the sun to the center of the milky way galaxy is around 26,000 light years. This is a scale where we can compress the history of the universe into a single year.