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Scales of the Universe (and a little refresher) www.astro.umass.edu/~mauro/astro100 Goals to refresh and use scientific notations to remember how to convert units! to see the levels of structure in the Universe to comprehend the vastness of scales in the Universe In order to describe and understand what you see, you need numbers and units Amherst: UMass is about 1.5 miles from the center; Antonio’s pizza is about 1 pound a slice The town was founded about 200 years ago The Universe: The nearest star is 4 light years away; The mass of a massive black hole is about 108 solar mass (1 solar mass is about 2*1030 Kg) The age of the Universe is about 14 billion years The scales we meet in exploring the Universe are very big, we must learn how to deal with them How to say big numbers Billion Million Thousand thousandth millionth billionth Giga Mega Kilo ... milli micro nano (G) (M) (K) 109 106 103 (m) (m) (n) 10-3 10-6 10-9 Units Conversion First of all – Units are good things! You can say the distance to Boston in miles (or km) instead of inches (or cm)! Translating to useful units is a very handy skill. The key to changing units is remembering to replace a unit by something equivalent Converting Units How many quarters are there in 1000 dollars? 1000 dollars= 1000x 1 dollar = 1000x 4 quarters = 4000 quarters Question: How many cm are there in 3 km? 3 km = 3x 1km = 3x 1000 m= 3000 m = 3000x 1m = 3000x 100 cm = 300000cm Light-time=Light traveling time=distance Car-traveling time as distance: Boston is about 1.5 hours away (assuming the speed of a car is 60 mph) The speed of light: c = Destination London Moon Sun Jupiter Nearest Star Most Distant Galaxy Distance (km) 6,000 385,000 1.5 x 108 7.8 x 108 4 x 1013 1.4 x 1023 5 3x10 km/s. Light Travel time 0.02 s 1.3 s 500 s (8.3 min) 43 min 4.3 years 14 billion years Whenever you see "light-(time)", that means we are talking about distance, not time. Examples 1 yr = 3.15 x 107 s (Earth revolves around the Sun once) 1 ly = (3 x 105 km/s) x 3.15 x 107 s = 9.45 x 1012 km =10 thousand billion km! Now… on to scales in the Cosmos... 52 feet across 1 mile across 160 kilometers across 1 mile = 1.61 kilometers Infrared photo 12,756 km 1,600,000 km =1.6 x 106 km Moon 1.6x108 km =1.6x1011m 1AU = 1.5x1011 m AU is a distance unit 1.6 x 1010 km, or a trillion (1012) times wider than the first picture! 32 AU 100 AU 10,000 AU Stars are so far apart from each other! If the Sun is a golf ball in NYC, the nearest star is a golf ball in Chicago!!! 106 AU = 17 ly 1 ly =63,000 AU = 1013 km 1700 ly 170,000 ly 1.7 x 107 ly The local group of galaxies 1.7 x 109 ly Basic classes of objects: Planets: Earth as one Stars Sun as one Galaxies Milky Way as one Their sizes Earth: 104 km poppy seed Sun: 106 km grape fruit Milky Way 1018 km Earth-Sun distance Universe 1023 km 100,000 Earth-Sun distance A Sense of Space 1. The Sun would hold 1.3 million Earths. i.e. the radius of the Sun is about 100 times that of the Earth. 2. There are ~100 billion "Suns" in a galaxy like our own Milky Way Galaxy. 3.Astronomers can see billions of galaxies. Your local address: So…How Big is the Observable Universe anyway? …about 14 billion-billion-billion centimeters in diameter or 14,000,000,000,000,000,000,000,000,000 cm or 1.4x1028 cm or 14 billion ly or 6000 Mpc Summary of concepts Various units and their conversion Order of magnitude Power of 10, exponent Scientific notation The speed of light Various scales of the Universe Our place in the Universe, both in space and time Assigned Reading for Next Class Chapter 2, “The Sky”, complete (p.12 to p.33) What is our address in the Universe? UMass, Amherst, Massachusetts U.S.A., Earth, Solar System Milky Way Galaxy, Local Group, Local Supercluster Our Universe