Chapter 2 Notes - ISP 205 - Chapter 2 Page 1 2.1 Patterns...


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ISP 205 - Chapter 2 Page 1 2.1 Patterns in the Night Sky I. Appearance of Universe from Earth A. Constellations 1. Well defined region of sky with borders; patterns of stars 2. 88 official constellations – names chosen in1928 by Astronomical Union B. Celestial Sphere 1. Imagining stars to lie on this that surrounds the Earth (Ancient Greeks) 2. Really lie at different distance from the Earth 3 . North Celestial Pole (North Pole) South CP (South Pole) Celestial equator (projection of the equator into space, makes a complete circle around the Celestial Sphere) Ecliptic (path the sun follows as it appears to circle around the celestial sphere once a year, crosses the celestial equator at 23.5º angle “tilt”) C. Milky Way 1. Shown on the celestial sphere (passing through more than a dozen constellations) 2. Relationship to Milky Way Galaxy : It traces our galaxy’s disk of stars-galactic plane-as it appears from our location in the outskirts of the galaxy 3. Shape: thin pancake with bulge in middle 4. Solar Systems is a little more than halfway 5. Farther out you are in the galaxy the more clear the view is with appropriate telescopes 6. Width varies a. Widest in the direction of the constellation Sagittarius (toward center bulge) Dark Lanes – Hidden Parts of the Galaxy 7. The dark lanes appear in the regions where particularly dense interstellar clouds obscure our view of stars behind them. 8. Abundant gas and dust prevents us from seeing more than a few thousand light years 9. Much of the galaxy was hidden until new technologies allowed us to peer through the clouds by observing forms of light that are invisible to our eyes (radio waves and x-rays) D. The Local Sky 1. Local Sky – the sky as seen from wherever you happen to be standing (takes shape of a hemisphere or dome) 2. Dome due to the fact that the ground block half of the celestial sphere 3. Horizon - boundary between Earth and Sky 4. Zenith – point directly overhead 5. Meridian – imaginary half circle stretching from the horizon due south, through zenith, to the horizon due north 6. We pinpoint an object in the local sky by stating its altitude above the horizon and direction along the horizon (sometimes stated in azimuth) E. Angular Sizes and Distances 1. Angular distance – between a pair of objects in the sky is the angle that appears to separate them. (Xº,X’,X”) a. Measured in degrees b. subdivided into 60 arcminutes (‘) c. subdivided into 60 arcseconds (“) 2. Stars Rising and Setting a. Stars moves from East to West
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ISP 205 - Chapter 2 Page 2 b. Stars relatively near the north celestial pole remain perpetually above the horizon. They never rise or set but instead make daily counterclockwise circles around the north celestial pole. Such stars are circumpolar. c. Stars relatively near the south celestial pole never rise above the horizon.
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