Lecture2

Lecture2 - Discovering the Universe for Yourself We had the sky up there all speckled with stars and we used to lay on our backs and look up at

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1 Discovering the Discovering the Universe for Yourself Universe for Yourself Mark Twain (1835 – 1910) American author, from Huckleberry Finn We had the sky, up there, all speckled with stars, and we used to lay on our backs and look up at them, and discuss about whether they was made, or only just happened. A Constellation is A Constellation is …a region of the sky, within official borders set in 1928 by the IAU. Recognizable by a pattern or group of stars. • Some patterns, like the Winter Triangle of Sirius, Procyon and Betelgeuse, span several constellations. Constellations Constellations • Most official names of the 88 constellations come from antiquity. Some southern hemisphere constellations were named by European explorers in the 17 th th centuries. The patterns of stars have no physical significance! Stars that appear close together may lie at very different distances. • Modern astronomers use constellations as useful general landmarks, but specify the exact location of objects by a system of celestial coordinates . Not to scale The Celestial Sphere The Celestial Sphere • The sky above looks like a dome…a hemisphere. . •I f w e imagine the sky around the entire Earth, we have the celestial sphere . • This a 2-dimensional representation of the sky; there is no physical sphere up there! Because it represents our view from Earth, we place Earth in the
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Parts of the Celestial Sphere Parts of the Celestial Sphere North & South celestial poles the points in the sky directly above Earth’s north and south poles celestial equator the extension of Earth’s equator onto the celestial sphere ecliptic the annual path of the Sun through the celestial sphere, which is just a projection of Earth’s orbital plane on the sky. (Remember, Earth goes around the Sun!) Understanding patterns in the sky Understanding patterns in the sky Describe the basic features of the local sky. How does the sky vary with latitude? Why are some stars above the horizon at all times? How does the night sky change through the year? Our goals for learning: Your next Lab will be in the Planetarium and you will learn more about these questions. Measuring the Sky Measuring the Sky We measure the sky in angles , not distances. • Full circle = 360º • 1º = 60 arcmin • 1 arcmin = 60 arcsec • 3600 arcsec = 1º NOTE: the Moon is about 0.5º, but so is the Sun! – A larger object farther away can have the same angular size as a smaller object closer to us 90º We may use terms like “angular distance” but we want an angle, not a distance! Measuring Angles in the Sky Measuring Angles in the Sky We say that the angular “distance” between these two stars in the Big Dipper is 5 degrees. There are about 9
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This note was uploaded on 02/20/2012 for the course ASTRO 3 taught by Professor Mclean during the Spring '11 term at UCLA.

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Lecture2 - Discovering the Universe for Yourself We had the sky up there all speckled with stars and we used to lay on our backs and look up at

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