ASTR 101 1st Edition Lecture 2 Outline of Last Lecture I 4 fundamental forces II Key terms Outline of Current Lecture Chapter 1 continued I The Universe II Scale of the solar system III Cosmic calendar Current Lecture I The Universe the sum total of all matter and energy everything with and between all galaxies a As astronomers we ask 2 questions i How did space and time come to be By the big bang ii How did this happen Most occurred from galaxies and stars Everything around us and us was once a star Stars made us come to be We are star stuff Hydrogen and helium came from the big bang The majority of a star s lifetime is spend in what we call the main sequence where it is burning hydrogen When a star tires and runs out of hydrogen it explodes and returns material to the interstellar media b We see objects as they occur in the past the farther away we look in the distance the farther back we see in time II Scale of the solar system a How big is the universe i The Milky Way is 1 of 100 billion galaxies ii There are as many stars as there are grains of dry sand on all the beaches on Earth iii 1022 stars are in the observable universe iv There are more planets than there are stars in the universe III Cosmic calendar a Look in the book at Figure 1 10 the cosmic calendar in 1 year These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute b How is Earth moving in our solar system i Earth s axis is tilted 23 5 degrees this contributes to the changing of the seasons If Earth did not have this tilt we would have a constant climate Also seasons are reversed in the Northern and Southern hemispheres c The Sun has a 230 million year orbit