ASTR 1205 Unit 1: A Modern View of the Universe PDF

ASTR 1205 Unit 1 Dr. Bryan Rowsell Unit 1: A Modern View of the Universe 1.1 The Scale of the Universe What would our “Cosmic Address” be if we could ascribe a mailing address, e.g. RDP has a Street, City, Province, Country, all aspects gettin...

ASTR 1205 Unit 1 Dr. Bryan Rowsell Unit 1: A Modern View of the Universe 1.1 The Scale of the Universe What would our “Cosmic Address” be if we could ascribe a mailing address, e.g. RDP has a Street, City, Province, Country, all aspects getting successively larger. In other words, if were to try to tell an alien where we are, what is the minimum amount of information they would need to locate us? 1. Planet (Earth) 2. Solar System (Sol) 3. Galaxy (Milky Way Galaxy) 4. Galactic Group (Local Group) 5. Supercluster of Galaxies (Local Supercluster) A Modern View of the Universe ·1−1· 1.1: The Scale of the Universe ASTR 1205 Unit 1 Dr. Bryan Rowsell a collection of stars held together by gravity and galaxy orbiting a common centre Our galaxy is referred to as the Milky Way, containing roughly: 100 billion, or 100,000,000,000 (i.e. 1×1011) stars! If you could count 1 star a second, it would take roughly 3000 years to count them all. Our galaxy is part of a local group of galaxies. galactic cluster a collection of galaxies relatively close in space, or group bound by gravity Small collections of galaxies are called groups, while larger collections of galaxies are called clusters. a collection of galactic groups and/or clusters, supercluster typically more concentrated than normal The collection of superclusters and isolated galaxies make up the known universe. At this point, it would be good to discuss units. Units (or dimensions) are important as they allow for dissemination of data across disciplines. Common units in astronomy are: astronomical Earth’s average distance to the sun, 150 unit (AU) million (or 1.5×108) kilometers (km) The distance light travels in one siderial year, light year (ly) 10 trillion (or 1.0×1013) km. parsec (pc) 3.2 ly or 206,265 (or 2.06×105) AU. Note that light year is a distance unit, not a unit of time, same with parsec (not that George Lucas would know). A Modern View of the Universe ·1−2· 1.1: The Scale of the Universe ASTR 1205 Unit 1 Dr. Bryan Rowsell Ramifications? The more distant we look in the universe, the further in time we are observing! For example: it takes the light from the sun 8 minutes to reach Earth, thus we are observing the Sun as it was 8 minutes ago. When we observe a distant galaxy or star, not only are we viewing the star as it was x years ago, but we’re even observing where it was x years ago! Scale of the Solar System: If the Sun is the size of a basketball…. 𝑑𝑠𝑢𝑛 = 𝑑𝑏𝑎𝑠𝑘𝑒𝑡𝑏𝑎𝑙𝑙 1400000 𝑘𝑚 = 25 𝑐𝑚 Thus, the scale is rough 1:56000… Where would Mercury, the planet closest to the Sun, be on this scale? roughly the door to the lecture theatre, and it would be a