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Astronomy & Astrophysics
Stefan Mochnacki

AST 201 1 Lecture 2 The Universe Universe: the totality of all space, time, energy, and matter, no outside; roughly 13.7 billion years old, therefore, we can only see things that are less than this far away, as we are looking back in time; Universe usually refers to the observable universe Light Year: distance light travels in one year = 9.46 trillion km Speed of light (c): 300 million ms Planets: spherical bodies which orbit stars directly; can be rocky, gassy, liquid or icy; now planets must have cleared their orbit Stars: enormous spheres of very hot gas which produce energy through nuclear fusion; produces more energy than it takes in Solar system: one or more planets orbiting a star; ours is roughly 1ly in length Galaxy: a collection of billions of stars all orbiting a common centre; we are in the Milky Way Galaxy, our nearest neighbour is the Andromeda Galaxy, both of them are spiral galaxies Local Group: a few dozen or so small galaxies make up ours, they orbit each other Galaxy Clusters: whole bunch of galaxy groups, galaxies are all organized into groups and the groups are all moving away from one another Super Clusters: enormous groups of galaxies all orbiting one another; 1000s or millions of galaxies, there is nothing in the universe much bigger; ours is called Virgo Super cluster because many of its galaxies appear to us in the direction of the constellation Virgo Science: the process of trying to find natural explanations for natural phenomena by repeatedly following a cycle of hypothesis, prediction, and observation or experiment; for something to be scientific it must be falsifiable (could be proven false if it is so) Lecture 2 Readings (1, 3.4, 3.5) Rotation: spin Orbit: revolution around the sun Astronomical Unit (AU): Earths average orbital distance; 150 million km www.notesolution.com
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