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Next up: Focus on our solar system Three motions of Earth are: – Rotation (spin on the axis) – Revolution, a.k.a. orbit (around the sun) – Precession (wobble of the rotation) Major features of our planets and dwarf planets Motions of the Earth: Rotation Causes day & night (Two ways to measure) Mean solar day (noon to noon) = 24 hours Sidereal day (360o) = 23 hr, 56 min, 4 sec. Represents the time required for a star to be in the identical position as the night before. Since the sidereal day is approximately 4 min shorter than the mean solar day, we use the mean solar day to set our calendar. Astronomers use the sidereal day. Difference is due to the revolution or orbit of the earth around the sun. Sidereal day vs. solar day 360o turn 4 min difference Motions of Earth: Revolution/Orbit Elliptical orbit (a.k.a. oval!) Perihelion = closest to sun, occurs about January 3 Aphelion = farthest from sun, occurs about July 4 Ecliptic = Imaginary plane that connects the orbit of the earth with the celestial sphere. Celstial Sphere? Imaginary bubble of the sky. Ancient astronomers thought it was REAL The Truman show QuickTime™ and a decompressor are needed to see this picture. Ecliptic Precession The earth’s axis currently points at Polaris (North Star) Eventually will be Vega Not static! Traces a circle every 26,000 years. A wobble, like a top. Effects the seasons, and has been suggested that it relates to global warming/cooling (alone = inaccurate due to rate of warming trend). Planets • Formed from a nebula (cloud of dust and gas). Cloud comes together due to gravity. • Three Categories – Terrestrial – Jovian – Dwarf The Planets Terrestrial planets(a.k.a. Inner/Rocky planets) – Small – Rocky – more dense – close to sun – no rings – thin atmosphere – Mercury,Venus, Earth, Mars The Planets Jovian planets (a.k.a. Outer/Gaseous planets) – Huge – gas giants = thick atmosphere, – much less dense (Saturn floats!), – rings, – beyond asteroid belt – Jupiter, Saturn, Uranus, Neptune The Planets Dwarf planets – Ceres, Pluto, Eris – What is a Dwarf planet? – Bigger than an asteroid, but not quite big enough. – Caused astronomers to redefine exactly what a planet IS. Poor Pluto! Planets must: 1. Orbit the sun. 2. Have enough mass to be round. 3. Dominate its orbit. Pluto doesn’t dominate (dances with Charon) Ceres doesn’t dominate, not round (asteroid belt) Eris doesn’t dominate (space junk) My Very Excellent Mother Just Served Us Noodles - Terrestrial Planets Mercury -smallest inner planet, closest to the sun, no atmosphere, revolves/orbits quickly, but rotates very slowly, has the greatest temperature extremes Venus-2nd planet from the sun, brightest “star” in the sky, has recently active volcanism and tectonic activity, “thick” atmosphere consisting of 97% CO2. My Very Excellent Mother Just Served Us Noodles - Terrestrial Planets Earth is next in line . . . Mars - Appears reddish through a telescope with white polar caps, has a very thin atmosphere, large dust storms with hurricane force winds (270 km/h) last for weeks; has mountains & volcanoes, temperatures range from -70oC to -100oC. My Very Excellent Mother Just Served Us Noodles - Jovian Planets Jupiter-Huge mass, hydrogen and helium atmosphere, Great Red Spot, rotates rapidly, appears banded, 28 moons resembling a small solar system (Jupiter needed to have been 10X larger to be a star!), has rings My Very Excellent Mother Just Served Us Noodles - Jovian Planets Saturn- The ringed one! Similar to Jupiter in size, atmosphere, and structure, winds reach 1500 km/hr, stormy, 31 moons. Uranus-rotates “lying down”, has rings Neptune- rings, active atmosphere, 1, 000+ km/hr winds, Great Dark Spot, 13 moons, nitrogen and methane atmosphere, low temps = -200oC. How big? How big? How big? Looking ahead First Lab: what we can observe in our sky. Second lab: Debunking 2012.