Astronomy Vocabulary from the Textbook Compiled

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Astronomy & Astrophysics
Michael Reid

Astronomy Vocab CHAPTER 1OUR PLACE IN THE UNIVERSE Solar SystemA star sometimes more than one and all the objects that orbit it Milky Way Galaxyname of our galaxy and the band of light we see in the night sky Galaxy huge collection of a few hundred million to more than a trillion stars bound by gravity Local Groupthe group of about 40 galaxies to which the Milky Way belongs Galaxy Clusterscollection of a few dozen or more galaxies bound together by gravity Superclusterslargest known structures in universe consisting of many galaxy clusters Universesum total of all matter and energy Big Bangevent thought to mark the birth of the universe Nuclear Fusionprocess when two or more smaller nuclei slam together to make a larger one Asteroidrelatively small rocky object orbiting a star Cometrelatively small icerich object that orbits a star Observable Universeportion of the entire universe that can be seen from Earth probably only a tiny part of theuniverse LightYearDistance light can travel in a year 946 trillion km Astronomical Unit AUaverage distance of Earth from sun 150 million km CHAPTER 3THE SCIENCE OF ASTRONOMY Ellipsetype of oval that is the shape of a bound orbit Focusone of two special points within an ellipse that lie along the major axis When one object orbits a second object the second object lies at one focus of the orbit Semimajor Axishalf the distance across the long axis of an ellipse Eccentricitymeasure of how much an ellipse deviates from a perfect circle centretofocus distance divided by length of semimajor axis Keplers Laws of Planetary MotionThree laws discovered by Kepler that describe the motion of the planets around the sun Keplers First Laworbit of each planet around the sun is an ellipse with the sun at a focus Keplers Second Lawas a planet moves around its orbit it sweeps out equal areas at equal times Planet moves faster at the sun perihelion and slower farther away aphelion Keplers Third LawSquare of a planets orbital period is proportional to the cube of its average distance from the sun semimajor axis the more distant a planet the slower the orbit pa CHAPTER 4MAKING SENSE OF THE UNIVERSE Speedhow far something goes in an amount of time Velocitytells speed and direction of an object Accelerationwhen velocity changes Acceleration of Gravityacceleration of a falling object 98 ms on Earth Momentummass x velocity Forceanything that can change momentum Net Forceoverall force to which an object responds mass x acceleration Angular Momentummomentum attributed to rotation m x v x r radius Torquetwisting force that can change an objects angular momentum Massamount of matter in something Weightdepends on mass and forces like gravity FreeFallcondition in which an object is falling without resistance weightless Newtons Laws of Motionthree basic laws that describe an objects reaction to force Newtons First Lawin the absence of net force an object moves at constant velocity Newtons Second Lawhow net force effects an objects motion forcemass x acceleration Newtons Third Lawfor every force there is an equal and opposite reaction force Conservation of Momentumin absence of net force total momentum remains constant Conservation of Angular Momentumin absence of net torque total angular momentum remains constant Conservation of Energyenergy can be neither created or destroyed it can only change form MassEnergyenergycontained in mass itself Bound Orbitorbit on which an object travels repeatedly around another object elliptical
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