ASTRO 100 NOTES - Introduction - The Night sky Astronomy:...

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Introduction - The Night sky Astronomy: study of all things outside the atmosphere of the Earth - Planets - Stars - Galaxies - Structure and evolution of universe Cosmology Milky Way contains over 200 billion stars only one of trillions of galaxies Constellations - Groupings of prominent stars which appear nearby in the sky - Includes the whole area in the sky, not just the stars. - In reality, stars are nowhere near each other Celestial Sphere - Coordinate system in the sky (like Latitude and Longitude) - Locations of stars, suns and planets can be specified on celestial sphere - Stars appear fixed with respect to each other not true in real life, but it is very small movement - Sun and planets move on the sphere throughout the year Daily Motions - Earth spins on its axis one time everyday o Causes day and night o Sun, Moon, and stars all move from East to West across the sky during the course of the day o North Star, Polaris, Does Not Move - Stars we see depend on our latitude on Earth - Vocab o Meridian: imaginary line running North-South Sun and stars reach their highest point when they reach the meridian o Zenith: point directly overhead - North Pole o Can only see stars North of Celestial Equator o North Star is directly overhead o Stars never rise or set = circumpolar They circle the North Star - Equator o All stars rise and set all day, every day o North and South Celestial Poles are near the horizon o Sun blocks some stars o No circumpolar stars o All stars appear to rise and set straight up from the horizon - Stevens Point o Cannot see most Southern stars o Some stars will always rise and set o Most Northern stars are circumpolar Yearly Motions
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- Earth travels around Sun once every year - It is tilted by 23.5 degrees with respect to the orbital plane - Sun lines up with different constellations during the year, blocking them - Ecliptic: path of the Sun through the Celestial Sphere not aligned with tilt of Equator due to tilt Of Earth - Zodiac: 12 constellations through which the ecliptic passes during the course of a year o 12 signs of Zodiac + Ophiuchus o My Actual sign: Ophiuchus Planetary Motion - Planets all move in the same plane about the Sun as the Earth, so they all appear to move around the Zodiac Summer Solstice - Longest period of daylight in Northern Hemisphere - Sun reaches highest point in sky for Northern Hemisphere - June 21 Autumnal Equinox - Equal periods of day and night for entire Earth - Sun crosses Celestial Equator - September 21 Winter Solstice - Longest period of darkness in Northern Hemisphere - Sun at lowest point in sky for Northern Hemisphere - December 21 Vernal Equinox - Equal periods of day and night for entire Earth - Sun crosses Celestial Equator - March 21 Seasons - Due to tilt of Earth with respect to orbital plane
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ASTRO 100 NOTES - Introduction - The Night sky Astronomy:...

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