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University of Toronto St. George
Astronomy & Astrophysics
Stefan Mochnacki

AST201 Universe Totality of space, time, energy, and matter No outside Big Bang: Beginning of the expansion of the universe About 13.7 billion years old Elements are manufactured by the recycling of stars Observable universe is separated from the rest of the universe by a horizon Observable universe is the part of the universe that the laws of physics allow us to see How much can be seen of the universe (Observable Universe)? 1) Speed of light = c = 300 million ms (in a vacuum) a. Light Year = DISTANCE light travels in one year = 9.46 trillion km b. Observation of objects many light years shows us what happened to those objects that many years ago (Since light takes time to travel to us, looking far away means we are looking back in time) c. Light from the end of the universe have not reached us d. Limit imposed by nature to how far we can see (Observable universe) e. Closest star is Alpha Centauri (4.4 light years away) Structures in the Universe 1) Planets spherical bodies which orbit stars directly; can be rocky, gassy, liquid, or icy a. Pluto = dwarf planet (has not cleared its orbit) 2) Stars enormous spheres of very hot gas which produce energy by nuclear fusion exp. Sun 3) Solar system one or more planets orbiting a star 4) Galaxy Collection of Billions of stars all orbiting a common center a. Most galaxies are rotating like a disk i. Virtually every galaxy outside the Local Group is moving away from us ii. The more distant the galaxy, the faster it appears to be racing away b. Earth is in the Milky Way galaxy (Spiral Galaxy) c. Closest (large) neighbor galaxy Andromeda Galaxy (Spiral Galaxy) 5) Local Group Few of the galaxies who all orbit one another a. All of the galaxy clusters in the Universe are moving apart from one another 6) Superclusters Enormous group of galaxies all orbiting one another (1000s or 1000000s of member galaxies) a. Our supercluster = Virgo Supercluster Science Process of trying to find natural explanations for natural phenomena by repeatedly following a cycle of hypothesis, prediction, and observation or experiment Scientific propositions must be falsifiable (can be proven false) Hypothesis Educated guess Scientific Method: 1) Make Observations, 2) Ask a question, 3) Suggest Hypothesis, 4) Make a Prediction, 5) Perform Test Motion Earths Rotation daily spin Earths Orbit Revolution around the sun (years) - Earth is on an axis tilt (results in seasons) 1) Speed Rate at which an object moves (ms) = distancetime 2) Velocity Speed and Direction 3) Accelerations any change in velocity units of speedtime)(ms Acceleration of Gravity All falling objects accelerate at the same rate (vacuum) g = 9.81 ms2 on Earth Does not change regardless of mass Momentum = mass x velocity Net force changes momentum, which generally means an acceleration Rotational momentum of a spinning or orbiting object is known as angular momentum Angular Momentum = mass x velocity x radius Mass amount of matter in an object Weight Force that acts upon an object Astronauts are weightless in space o There is gravity in space
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