The Scale of the Cosmos Scale defined as relative magnitude. Astronomy deals with objects on a vast range of size scales and time scales. Most of these size and time scales are way beyond our every-day experience. #1 An Average Classroom Order of magnitude = Power of ten Each jump in scale will be 2 orders of magnitude or a factor of 100 in distance. The classroom is roughly one order of magnitude larger than the human height scale. Approx. Scale: 52 x 52 ft #2 - A City View Scale: 5200 x 5200 ft 1 mile x 1 mile Jumping 2 orders of magnitude 10 x 10 = 10 2 = 100 1
Metric System of Units MKS units Meter (m) for length Kilogram (kg) for mass Second (s) for time Uses prefixes to express large or small quantities. kilo- k 1000 thousand Mega- M 1,000,000 million Giga- G 1,000,000,000 billion Example: 5 Ms = 5,000,000 seconds #3 Southern California Scale: 100 miles x 100 miles 160 x 160 km 4 orders of magnitude larger than classroom. Scale factor = 10,000 Conversion factor for distance 1 mile = 1.6 kilometers Which unit is a longer measure of distance? A.Mile B.Kilometer 2
#4 - Earth Diameter of the Earth: 12,756 km Scale: 16,000 x 16,000 km 1.6 x 10 4 km 6 orders of magnitude Scale factor = 1,000,000 = 10 6 Scientific Notation A convenient way to write very large or very small numbers that excludes placeholder zeros. Examples: 45,600 = 4.56 x 10 4 0.0000581 = 5.81 x 10-5 index Index is used to indicate the magnitude of a number. 10 3 thousand 10 6 million 10 9 billion Which of the following numbers is the expanded form of 5.01 x 10 5? A. 51,000 B. 5,010 C. 501,000 D. 50,100 3
What is the magnitude of the following number? 2.96 x 10 8 A. ten million B. hundred million C. billion D. ten billion #5 - Earth and Moon Average Distance Earth Moon: 384,000 km Scale: 1.6 x 10 6 km #5 (Earth and Moon) or Sun Diameter of the Sun: 1.4 x 10 6 km = Scale: 1.6 x 10 6 km 4
# 6 Earth s orbit around the Sun Average Distance Sun Earth = 150,000,000 km Scale: 1.6 x 10 8 km 1 AU Distances in the solar system In order to avoid large numbers beyond our imagination, we introduce new units: 1 Astronomical Unit (AU) = Avg. Distance Sun Earth ~ 150 million km #7 - The Solar System Scale: Approx. 100 AU 5
# 8 - Local Space Around our Solar System Scale: Approx. 10,000 AU #9 - The Solar Neighborhood Scale: Approx. 1 million AU The Solar Neighborhood 1 million AU is too large to express stellar distances New distance scale: 1 light year (ly) Distance traveled by light in 1 year = 63,000 AU = 10 13 km = 10,000,000,000,000 km Approx. 16 light years Nearest star to the Sun: Proxima Centauri, at a distance of 4.2 light years 6
If we wanted to accurately represent the distance between stars TO SCALE, where on Earth would a basketball have to be placed to represent the distance between the Sun (placed in Lancaster) and Proxima Centauri? A. Somewhere on campus B. In the next city C. In the next state D. Somewhere in Europe #10 - The Extended Solar Neighborhood Scale: Approx. 1,600 light years #11 - The Milky Way Galaxy Diameter of the Milky Way: ~ 100,000 ly Scale: 160,000 light years 50,000 pc = 50 kpc 7
Let s scale down the Milky Way (~100,000 ly across) to the size of the continental United States (~3000 miles across). What distance would represent the nearest stars? the solar system? #12 - The Local Group of Galaxies Distance to the nearest large galaxies: several million light years Scale: 5,000 kpc = 5 Mpc If we wanted to accurately represent the distance between galaxies TO SCALE, where on Earth would a basketball have to be placed to represent the average distance between the Milky Way (placed in Lancaster) and a member of the local group of galaxies? A. Somewhere on campus B. In the next city C. In the next state D. Somewhere in Europe 8
#13 - Large Scale Structure Clusters of galaxies are grouped into superclusters. Superclusters form filaments and walls around voids. Scale: 500 Mpc 16.3 billion light years 24 orders of magnitude larger than the classroom. Common units of distance used in astronomy Unit Kilometer (km) Astronomical Unit (AU) Light year (ly) Parsec (pc) Kiloparsec (kpc) Megaparsec (Mpc) Purpose Distance to the Moon; Size of an object found in the solar system Distance within a solar system Distance to another star Large scale distances within a galaxy Distance to another galaxy Complete the statement: The galactic center is located about 7.6 away from the Earth. A. astronomical units B. light years C. kiloparsecs D. megaparsecs 9
Complete the statement: Eris is the largest known dwarf planet in the Solar System (roughly 27% more massive than Pluto) and the ninth largest body known to orbit the Sun directly. It s current distance from the Sun is 96.7. A. astronomical units B. light years C. kiloparsecs D. megaparsecs Eris (center) and Dysnomia taken by the Hubble Space Telescope. 10