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Astronomy: The Final Review (Part 1of 2)Chapter 1: Our Place in the Universe•Solar system is 8 classical planets, dwarf planets, asteroids, and comets inside the Milky Way•Milky Way is a flattened collection of stars, gas, dust; Milky Way is a member of the Local Group, made up of a few dozen galaxies, Milky Way and Andromeda are giants within it, Local Group is part of the Virgo Super-cluster•Big Bang happened 13.7 million years ago•our bodily elements come from death of stars•astrobiology: possibilities of life elsewhere in our SS and beyond•Occam’s Razor: a guiding principle in science stating that when we are faced with two hypotheses that explain a particular phenomenon equally well, we should adopt the simpler of the two•Cosmological principle- on a large scale, the universe is the same ev-erywhere•math is the language of science!Chapter 2: Patterns in the Sky: Motions of Earth•Apparent Daily Motion: the path each celestial body makes across the sky•Polaris is almost directly above the North Pole, at the North Celestial Pole (which is always 90º away from the celestial equator)•The earth is at the center of the Celestial sphere, meridian divides the sky into east and west halves, runs through the Zenith (point directly aboveyou) and Nadir (point directly below you)•noon= when the Sun crosses the meridian, midnight= when the Sun cross the meridian on the other side of Earth•REMEMBER: even at its highest point, the Sun never reaches the Zenith (point directly above you).•Ecliptic: Sun’s apparent annual path around the celestial sphere. Re-ally, the sun is stationary, our view of stars changes as the Earth moves along its orbit, making it look like the Sun is moving against the back-ground of stars. •At the North Pole, nothing rises or sets, you always see the same half of the celestial sphere, at the South Pole you see the opposite half, and ev-erything spins clockwise around the SCP•Latitude is the angle between the radius of the Earth to your position, and the radius of the Earth to the nearest point on the Equator (so at the equator, it’s 0, at the poles, 90)•The NCP moves with the viewer, but is always parallel to the NP, celes-tial equator moves with the viewer too, but always parallel to the real equa-tor•Declination (Dec): like latitude, it’s the N/S position on the Celestial sphere, -90º to +90º (think, horizontal lines, flat like a pool “DECk”), mea-sured in degrees•Right Ascension: like longitude, it’s the E/W position on the Celestial sphere, 0 to 24 hours, runs through N and S Celestial poles, 0 at meridian•At 30º N latitude, the NCP is in the middle of the sky, the stars move counterclockwise around it; stars located close enough to the NCP are cir-cumpolar stars, they don’t rise/set•From the Poles: we will always see the same half of the sky. From the equator: In one day, we will see the whole sky pass through our view. In be-tween: we see part of the sky all day and different parts at different times.•Earth is 1 AU from the Sun, the 23.5º tilt of the axis from the ecliptic causes seasons. When the NP is tilted to the Sun, the Sun is north of the ce-lestial equator (“midnight sun” at NP), meaning it can bee seen above the horizon fro over 12 hours, causing the long days of summer, because it’s higher in the sky, the light strikes the ground more directly, causing the heat.•Directness of sunlight and differing length of night account for Temp. change between seasons•Summer solstice: NP tilted farthest to sun, June 21st, Winter solstice: furthest away, Dec. 22nd•Autumnal equinox: equal day/night, Sun directly over equator, Sept. 23, Vernal equinox: where ecliptic and CE intersect, RA is 0, Mar 21st•One vernal equinox to the next is about 365.25 days, leap years make up for this•The constellations along the ecliptic are the constellations of the zodiac•Earth’s axis wobbles, taking 26,000 years to complete one cycle, celes-tial equator moves with the axis, so the equinoxes change too (Precession of the Equinoxes)•Moon has synchronous rotation: it rotates, but it’s elongated and the near side always falls toward Earth, far side gets illuminated during our New Moon•New moon: rises at sunrise, sets at sunset, then waxing crescent, east of the sun, sets a little after sunset, first quarter rises at noon, sets at mid-night, waxing gibbous, then full moon, rises when sun sets, then all waning phases•Solar eclipse: when Earth moves through the shadow of the Moon (to-tal, partial, and annular-almost total but ring of light around moon), must be in moon’s tiny shadow to see it•Lunar eclipse: moon is illuminated by red light from the Sun bent as it travels through Earth’s atmosphere before hitting the moon, anyone on thecorrect hemisphere can see it•How could we prove Earth is a sphere: 1) stars are visible from differ-ent spots at different angles, 2) ships going out to sea drop below the hori-zon, 3) lunar eclipses show curved edge•Copernicus: estimated planet distance, used to predict locations, brought forward heliocentric idea, Brahe, Galileo, Kepler helped prove it•Apparent Retrograde motion: just like when we pass a slower car and itseems to be moving backwards, differences in planetary orbit sizes and speeds make some appear to move back•Tycho Brahe: last great astronomer before telescope, assistant, Kepler,used data to deduce empirical (describe, don’t explain) laws based on ob-servations of Mars, replaced Copernicus’ circular orbits with ellipses1) Kepler’s first law: orbit of a planet is an ellipse, Sun’s at one focus, e is eccentricity (0-1)2) Kepler’s second law: when a planet has a smaller space to “sweep” it orbits slower3) Kepler’s third law: period squared is equal to distance cubed. Small Angle Formula: L = 2πDA/360º624 BC: Thales, philosopher, rejected superstition but thought Earth floats in a large ocean560 BC: Pythagorus, came up with Pythagorean Theorem, thought Earth was a sphere428 BC: Plato, space is infinite, contains spherical universe, center is Earth348 BC: Aristotle, Plato’s student, circular motion, geocentric system, 55 ce-lestial spheres, 4 elements, Earth•Air•Fire•Water310 BC: Aristarchus, heliocentric model, wasn’t recognized until Copernicus276 BC: Eratosthenes, determined circumference of Earth [angle of Sun at Syrene (vertical) and Alexandria (7º), 5000 stadia apart, so C=πD]Chapter 3: Laws of


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FSU AST 1002 - Final Review

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