Astronomy Ch 4

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Title:	Astronomy Ch 4
Description:	center of mass The balance point of a body or system of masses. The point about which a body or system of masses rotates in the absence of external forces. (p. 69) <br />circular velocity The velocity an object needs to stay in orbit around another object. (p. 68) <br />closed orbit An orbit that returns to the same starting point over and over. Either a circular orbit or an elliptical orbit. (p. 69) <br />deferent In the Ptolemaic theory, the large circle around Earth along which the center of the epicycle was thought to move. (p. 51) <br />eccentricity, e A number between 1 and 0 that describes the shape of an ellipse. The distance from one focus to the center of the ellipse divided by the semimajor axis. (p. 59) <br />ellipse A closed curve around two points called the foci such that the total distance from one focus to the curve and back to the other focus remains constant. (p. 58) <br />epicycle The small circle followed by a planet in the Ptolemaic theory. The center of the epicycle follows a larger circle (the deferent) around Earth. (p. 51) <br />equant In the Ptolemaic theory, the point off center in the deferent from which the center of the epicycle appears to move uniformly. (p. 51) <br />escape velocity The initial velocity an object needs to escape from the surface of a celestial body. (p. 69) <br />geocentric universe A model universe with Earth at the center, such as the Ptolemaic universe. (p. 50) <br />geosynchronous satellite A satellite that orbits eastward around Earth with a period of 24 hours and remains above the same spot on Earth's surface. (p. 68) <br />heliocentric universe A model of the universe with the sun at the center, such as the Copernican universe. (p. 49) <br />hypothesis A conjecture, subject to further tests, that accounts for a set of facts. (p. 59) <br />inverse square relation A rule that the strength of an effect (such as gravity) decreases in proportion as the distance squared increases. (p. 66) <br />mass A measure of the amount of matter making up an object. (p. 66) <br />natural law A theory that is almost universally accepted as true. (p. 59) <br />neap tide Ocean tide of low amplitude occurring at first- and third-quarter moon. (p. 71) <br />open orbit An orbit that carries an object away, never to return to its starting point. (p. 69) <br />paradigm A commonly accepted set of scientific ideas and assumptions. (p. 54) <br />parallax The apparent change in position of an object due to a change in the location of the observer. Astronomical parallax is measured in seconds of arc. (p. 50) <br />retrograde motion The apparent backward (westward) motion of planets as seen against the background of stars. (p. 50) <br />semimajor axis, a Half of the longest diameter of an ellipse. (p. 58) <br />spring tide Ocean tide of high amplitude that occurs at full and new moon. (p. 71) <br />theory A system of assumptions and principles applicable to a wide range of phenomena that have been repeatedly verified. (p. 59) <br />uniform circular motion The classical belief that the perfect heavens could only move by the combination of uniform motion along circular orbits. (p. 50)
Number of Cards:	25
Author:	thesuhys13
Created:	2006-04-30
Tags:	astronomy
Private:	No
Favorite Count:	1
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