ASTR 101 1st Edition Lecture 2 Outline of Last Lecture I. 4 fundamental forcesII. Key termsOutline of Current Lecture—Chapter 1 continuedI. The Universe,II. Scale of the solar system,III. Cosmic calendarCurrent LectureI. The Universe = the sum total of all matter and energy; everything with and between all galaxiesa. 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 galaxiesii. 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 universeiv. There are more planets than there are stars in the universe!III. Cosmic calendara. Look in the book at Figure 1.10- the cosmic calendar in 1 yearThese 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