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Astronomy Notes Historically Earth was thought to be center of solar system (geocentric model) Heliocentric model is correct (Sun centered solar system) On Earth celestial objects appear to move from east to west in an arc pattern Sun/Stars Apparent Path #1 Looking North at Polaris #2 Looking West #3 Looking South #4 Looking East This apparent motion is due to Earth’s counterclockwise rotation at 15 o /hour A solar day is from one solar noon (meridian or longitude) to the next The earth revolves in a tilted position 360 o around the sun (approx. 1 o /day) counterclockwise direction in an elliptical orbit Earth seasons are caused by the tilted revolution around the sun - not distance! Closer in the winter time (tilted away), further away in the summer time (tilted towards) Aphelion – Greatest distance away from sun in orbit (summer in N. Hemisphere) Sun’s diameter appears smallest in sky, slowest orbital velocity Perihelion – Closest distance to sun in orbit (winter in N. Hemisphere) Sun’s diameter appears largest in sky, fastest orbital velocity Dec. 21 Winter Solstice Direct Ray 23.5o S. Tropic of Capricorn Nights get longer, days shorter as you move higher in latitude 90o N. Endless night! June 21 Summer Solstice Direct Ray 23.5o N. Tropic of Cancer Nights get shorter, days longer as you move higher in latitude 90oN. Endless day! The earth rotates counterclockwise from west to east at 15 o /hour = 1 time zone 15 o /hour x 24 hours = 24 time zones on a 360 o sphere Evidence of Earth’s rotation 1) Foucault’s Pendulum (appears to turn) 2) Coriolis Effect (right deflection in N. Hemisphere) MOON The moon orbits the earth counterclockwise in an elliptical orbit on a 5o tilt Gravity and Inertia keeps moon in revolution, 1/2 illuminated by sunlight Moon ¼ dia. of Earth, 1/6th gravity, 120 lbs on earth = 20 lbs on moon One moon revolution = one moon rotation, back side of moon never faces Earth 27 1/3 Days to make one complete revolution around Earth, 29 ½ days for complete phases Apogee – Greatest distance away from Earth (appears smaller diameter) Perigee – Closest distance to Earth (appears larger diameter) Because the Earth and moon revolve as well as rotate the Earth must rotate more than 360o to return to the same meridian (solar noon or daily moon position) Lunar eclipse– occurs only at Full Moon, Earth’s shadow cast on moon Sun-Earth-Moon Solar eclipse – occurs only at New Moon, moon’s shadow cast on Earth Sun-Moon-Earth PLANETS Inner solid terrestrial planets Mercury, Venus, Earth, Mars Mercury 1st planet, 2nd smallest, no atmosphere, no moons Venus has CO2 atmosphere, hottest planet due to greenhouse effect, sister planet to Earth, clockwise rotation (retrograde motion), no moons Earth only planet with water/life, 1 moon Mars – red planet, thin CO2 atmosphere, 2 moons – Phobos & Deimos Asteroid Belt between Mars and Jupiter Jupiter – largest plane, ring system, fastest rotation (shortest day), 4 major moons, has rings & the Great Red Spot Saturn – ring system, many moons (18) Uranus – has rings, many moons (18), “tipped over” about 90 degrees to orbit plane Neptune – ring system, 8 moons Triton has a retrograde orbit (clockwise), can orbit further out than Pluto Pluto – half ice/half rock, highly eccentric orbit (very oval), over 90 degree axis tilt (points south), has one moon Charon. 10th planet – UB 313 has moon Meteor-Meteorite- Meteoroid Outer Gas Planets Jupiter, Saturn, Uranus, Neptune - all have “rings” Jupiter largest planet, gas giant, less dense Pluto/Charon and 10th Planet UB 313/moon are small, solid moon-like. Comets – “dirty snowballs”, huge elliptical orbits, tails point away due to solar wind Geometry of Orbits Revolution – movement of one celestial body around another Orbit – path taken during revolution All planets and comets have elliptic al orbits (oval) The eccentr icity or “out-of-roundness” of an ellipse can be calculated: Eccentricity = Distance between major foci Length of major axis Gravitation is the attractive force between all objects The greater the mass the greater the gravity STARS H-R Diagram - Luminosity vs. Temperature/Color The Sun is an average star Star power = fusion H He Sunspots – dark magnetized spots (usually pairs) travel across equator of Sun as Sun rotates Milky Way – Spiral galaxy, Solar System/Earth located halfway across on spiral band The universe is expanding as evidenced by the RedShift or Doppler Effect Galaxies are moving out and expanding, this stretches light beams out/longer wavelength Spectral shift of objects moving away is towards the red wavelength (red shift)