1.1 cosmic perspective.pdf

1.1 Cosmic Perspective ˆ What is large? What is small? Consider walking from San Diego to Los Angeles. An example of a scale model is a globe. Perhaps the scale is 1 inch = 1000 miles. ˆ Solar System. What is the solar system? For now, let’s say Sun, planets, moons, asteroids, & comets (no other sta...

1.1 Cosmic Perspective ˆ What is large? What is small? Consider walking from San Diego to Los Angeles. An example of a scale model is a globe. Perhaps the scale is 1 inch = 1000 miles. ˆ Solar System. What is the solar system? For now, let’s say Sun, planets, moons, asteroids, & comets (no other stars!). (“My Very Excellent Mother Just Served Us Noodles.”) The scale is 1:1010. (In astronomy we use scientific notation for large numbers.) No units are needed because they’re the same on both sides. (A person would be 107 miles tall in this model.1) The relative sizes are easy to show in a book or on a screen, as are the relative distances. [sketches 1 & 2] In sketch #2, an easy way to remember the approximate relative distances from the Sun to the eight planets is as follows: 1/3, 2/3, 1, 3/2, 5, 10, 20, 30. But showing both the relative sizes and distances in the a single scale model can’t be done in a book or on a screen. Could we walk to α Centauri, 4.4 light years away? ˆ Milky Way. What is the Milky Way? It’s our galaxy, full of stars, dust, & gas. There are more than 1011 stars in our galaxy. How much is a hundred billion? (Consider salt in Snapdragon...) The scale is 1:1019. Or, 1 mm = 1 light year. (A light year is the distance light travels in one year, roughly equal to 1013 km.) Or, atom-size = star-size. In this model, our Milky Way would be the size of a football field – with the Sun at about the 20 yd. line. ˆ Alternate Milky Way model. If the d is a grain of NaCl, the next grain is 7 miles away. This model is useful when visualizing galaxy collisions. ˆ Universe. The universe is everything that exists. There are more than 1011 galaxies in the universe. Ñ 1022 stars. How much is 1022? (Consider grains of sand... ) ˆ In astronomy, it’s not acceptable to confuse the solar system, the galaxy, and the universe.2 ˆ Time. Now the scale model is 1 year = age of universe. (The age of the universe is about 13.8 billion years.) January 1: big bang (the beginning of space, time, matter, energy, force,...) January: Milky Way forms September 3: Earth forms September 22: earliest life on Earth December 26: rise of dinosaurs 1Model sizes in mm for the Sun and 8 planets are as follows: 139,.5, 1.2, 1.3,.7, 14.3, 12.0, 5.2, and 4.8. Model distances in m from the Sun to the 8 planets are as follows: 6, 11, 15, 23, 78, 143, 287, and 450. 2htwins.net; The Known Universe by AMNH; cosmic eye; atlasoftheuni- verse.com; Cosmic Voyage. J. M. Veal, Principles of Astronomy 3 December 30: extinction of dinosaurs Dec. 31, 9 p.m.: earliest human ancestors Dec. 31, 11:58 p.m.: first modern humans Dec. 31, 11:59:25 p.m.: rise of agriculture Dec. 31, 11:59:49 p.m.: pyramids at Giza Dec. 31, 11:59:59 p.m.: Kepler, Galileo ˆ Motions. How does Earth move? Like a top on a record player on a merry-go-round. motion speed period rotation 600 mph 1 day precession 26,000 yrs revolution 60,000 mph 1 year galactic orbit w/ “bounce” 600,000 mph 230 ˆ 106 yrs Milky Way toward Andromeda 180,000 mph expansion of universe v “ H0r