ASTR lecture notes - Reference Systems: Sky- Celestial...

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Reference Systems:Sky- Celestial sphere,equator…North/south celestial Pole…Declination…Right ascension(imaginary concepts)NCP is Polaris, the north star…SCP is never visible from this far northDeclination=latitude but in the skyEarth- Surface, equator, North/South Pole, Latitude, LongitudeoWhy earth isn’t flat:Lunar Eclipse: Earth’s shadow is cast upon the moon…the shadow was an arc; therefore, theobject is circularOceans: the oceans bulge so two ships cant see eachother decks since the other boat is below thecurve.Magalenic Clouds: Magellen went far enough south to see stars/galaxies that no one in Europehad seen before.Divernal MotionThe earth (from looking down at the north pole) is rotating counter-clockwiseAt north pole: the NCP is directly overhead…the stars are always levelAt equator: All stars rise and set (you can see all the stars)…NCP and SCP are on horizon..starsgo up and downLatitude: The angle to the horizon..some stars are circumpolar,rise and set, and some are nevervisibleCelestial Equator: where the sun path is on Mar21, sept22 (autumnal and vernal equinox)…Autumnal= sun is moving southward…Vernal= northwardWinter soltice= Dec.21…Summer soltice= June 21Precession=(think of spinning top) circular motion but takes a long time (25,800 years) it’llrotate 47 degress awayEarth goes around the sun in a counter-clockwise motion8/31/11Earth’s tilt= 23.5 degreesEcliptic= apparent path of the sun around the celestial sphereElicptic and celestial equator are separated by 23.5 degreesEquinox=ecliptic and the equator crossWinter solstice= sun is farthest south from the celestial equator…summer solstice is northThe changes in season DON’T mean we are closer to the sun in summer than winter..itsthe tilt of the earth.Solar constant=1370 Watts/meters^2…AT BEST the sun delivers this much energy (its isactually less due to the ozone and radiation)Sun is high in the sky…more energy…hotter and vise versaThe sunlight is closer to perpendicular in summerEARTH= Ellipse, Sun at Focus, Counterclockwise, Ecliptic, 365.26MOON= Ellipse orbit, Earth at focus, Counterclockwise, tipped 5degrees from ecliptic, 1month9/7The MoonNew moon= when moon is between earth and the Sun
Sidereal Month= time it takes the moon to do an orbit…27.3days…This is the new moonso the new moon isn’t always between the Earth and the Sun therefore lunar eclipsesdon’t always happen.Synodic Month= the moon actually has to go a little bit farther since the Earth is movingas well…29.5daysThe moon is always half litSynchronous rotation: The moon spins counterclockwise…it takes the same amount oftime for the moon to spin as it does to orbit the Earth…Therefore; we always see thesame side of the moonPhases: determined by how much of the bright side we see…light goes from RIGHT toLEFT till full…then darkness goes RIGHT to LEFT till New MoonRight side is bright…Waxing (means getting bigger)

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Term
Spring
Professor
TonyWong
Tags
Solar System, Planet

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