chapter 2

chapter 2 - Chapter 2 Discovering the Universe for Yourself...

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Chapter 2 Discovering the Universe for Yourself
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2.1 Patterns in the Night Sky What does the universe look like from Earth? Why do stars rise and set? Why do the constellations we see depend on latitude and time of year? Our goals for learning:
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What does the universe look like from Earth? With the naked eye, we can see more than 2,000 stars as well as the Milky Way.
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Constellations A constellation is a region of the sky. 88 constellations fill the entire sky.
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Thought Question The brightest stars in a constellation… all belong to the same star cluster. all lie at about the same distance from Earth. may actually be quite far away from each other.
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Thought Question The brightest stars in a constellation… all belong to the same star cluster. all lie at about the same distance from Earth. may actually be quite far away from each other.
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The Celestial Sphere Stars at different distances all appear to lie on the celestial sphere. The ecliptic is the Sun’s apparent path through the celestial sphere.
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The Celestial Sphere The 88 official constellations cover the celestial sphere.
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The Milky Way A band of light that makes a circle around the celestial sphere. What is it? Our view into the plane of our galaxy.
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The Milky Way
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The Local Sky An object’s altitude (above horizon) and direction (along horizon) specify its location in your local sky.
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The Local Sky Zenith: The point directly overhead Horizon: All points 90° away from zenith Meridian: Line passing through zenith and connecting N and S points on the horizon
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We measure the sky using angles
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Angular Measurements Full circle = 360º = 60 (arcminutes) 1 = 60 (arcseconds)
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Thought Question 60 arcseconds 600 arcseconds 60 × 60 = 3,600 arcseconds The angular size of your finger at arm’s length is about 1°. How many arcseconds is this?
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Thought Question 60 arcseconds 600 arcseconds 60 × 60 = 3,600 arcseconds The angular size of your finger at arm’s length is about 1°. How many arcseconds is this?
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Angular Size angular size = physical size ´ 360 degrees 2p ´ distance An object’s angular size appears smaller if it is farther away.
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Why do stars rise and set? Earth rotates west to east, so stars appear to circle from east to west.
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Our view from Earth: Stars near the north celestial pole are circumpolar and never set. We cannot see stars near the south celestial pole. All other stars (and Sun, Moon, planets) rise in east and set in west. Celestial equator Your horizon A circumpolar star never sets This star never rises
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Thought Question What is the arrow pointing to? A. The zenith B. The north celestial pole C. The celestial equator
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What is the arrow pointing to? A. The zenith
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This note was uploaded on 06/04/2010 for the course ASTR 110G taught by Professor Unknown during the Fall '09 term at NMSU.

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chapter 2 - Chapter 2 Discovering the Universe for Yourself...

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