Astronomy The Final Review Part 1 of 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 90 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 above you 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 90 to 90 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 30 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 5 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 furthest away Dec 22nd Summer solstice NP tilted farthest to sun June 21st Winter solstice 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 the correct hemisphere can see it 1 2 3 1 2 3 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 it seems 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 ellipses Kepler s first law orbit of a planet is an ellipse Sun s at one focus e is eccentricity 0 1 orbits slower Kepler s second law when a planet has a smaller space to sweep it Kepler s third law period squared is equal to distance cubed Small Angle Formula L 2 DA 360 624 BC Thales philosopher rejected superstition but thought Earth floats in a large ocean 560 BC Pythagorus came up with Pythagorean Theorem thought Earth was a sphere 428 BC Plato space is infinite contains spherical universe center is Earth 348 BC Aristotle Plato s student circular motion geocentric system 55 ce lestial spheres 4 elements Earth Air Fire Water 310 BC Aristarchus heliocentric model wasn t recognized until Copernicus 276 BC Eratosthenes determined circumference of Earth angle of Sun at Syrene vertical and Alexandria 7 5000 stadia apart so C D Chapter 3 Laws of Motion Galileo was the first to use a telescope from Pisa saw moon s craters demonstrated that Earth s gravity accelerates all objects at the same rate independent of mass discovered Jupiter s 4 largest moons and Venus phases together these proved the heliocentric model wrote a book thought to attack Pope placed under house arrest most of