ast test 1

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ast test 1
2010-09-22 15:22:51

vocab and concepts
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  1. solar system
    • our sun and all the objects that orbit it
    • located a little over halfway from the galactic center to the edge of the galactic disk
  2. Milky Way Galaxy
    • our disk-shaped collection of stars
    • contains more than 100 billion stars
  3. galaxy
    • great island of stars in space
    • contains between a few hundred million to a trillion or more stars
  4. local group
    the group of about 40 galaxies to which the Milky Way belongs
  5. galaxy clusters
    • a collection of a few dozen or more galaxies bound together by gravity
    • smaller collections of galaxies are simply called groups
  6. universe
    the sum total of all energy and matter
  7. expanding
    • the idea that the space between galaxies or clusters of galaxies is growing with time
    • caused by the Big Bang
  8. nuclear fusion
    he process in which two (or more) smaller nuclei slam together and make one larger nucleus
  9. light year
    the distance that light can travel in 1 year, which is 9.46 trillion km
  10. observable universe
    the portion of the entire universe that, at least in principle, can be seen from Earth
  11. rotation
    the spinning of an object around its axis
  12. orbit or "revolution"
    the orbital motion of one object around another
  13. astronomical unit (au)
    the average distance (semimajor axis) of Earth from the Sun, which is about 150 million km
  14. ecliptic plane
    the plane of Earth's orbit around the Sun
  15. axis tilt
    the amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic plane
  16. what is your universal address?
    universe -> local supercluster -> local group -> milky way galaxy -> solar system -> north america -> USA -> Florida -> Orlando -> Main Campus -> MAP 260
  17. our cosmic origins (figure 1.2)
  18. constellations
    • a region in the sky with well-defined borders
    • there are 88 official constellations
  19. why do stars rise and set?
    • because all stars have daily circles that are partly above and partly below the horizon, they appear to rise and set because Earth rotate from west to east
    • stars in the north celestial pole do not rise or set but are circumpolar (make daily counterclockwise rotations)
    • stars in the south celestial pole do not rise above the horizon
  20. how does latitude affect constellations?
    • it affects the locations of the horizon and zenith relative to the celestial sphere
    • the altitude of the celestial pole in your sky is equal to your latitude
  21. celestial sphere
    • the imaginary sphere on which objects in the sky appear to reside when observed from Earth
    • 4 points: north celestial pole - south celestial pole - celestial equator - ecliptic
  22. Milky Way
    • the band of light that circles all the way around the celestial sphere
    • it traces our galaxy's disk of stars (the galactic plane) as it appears from our location in the outskirts of the galaxy
  23. angular sizes and angular distances
    size - the angle it appears to span in your field of view, does not tell us an object's true size, the further the object the smaller the angular size

    distance - the angle that appears to separate two objects in the sky
  24. what causes seasons?
    • the Earth's axis tilt causes sunlight to fall differently on Earth at different times of the year
    • has nothing to do with the Earth's distance from the Sun
    • Earth's axis tilt is 23.5 degrees, always pointed towards Polaris
  25. solstices
    • summer (June) solstice - June 21, northern hemisphere receives more direct sunlight that the southern hemisphere, the sun is at its highest at noon
    • winter (December) solstice - December 21, northern hemisphere receives its least direct sunlight, the sun is at its lowest at noon
  26. equinoxes
    • spring (March) equinox - March 21, the moment when the northern hemisphere is being tipped slightly toward the sun
    • fall (September) equinox - September 22, the northern hemisphere first starts being tipped away from the sun

    • the sun rises precisely due east and sets precisely due west
    • the sun falls equally on both hemispheres
  27. precession
    • the wobble of the earth on it's tilt
    • DOES NOT change the earth's tilt (always remains at 23.5 degrees)
    • caused by gravity's effect on a tilted rotating object that is not a perfect sphere
  28. moon phases (lunar phases)

    • half of the moon is always illuminated by the sun, but the amount we see depends on the Moon's position in orbit
    • 29.5 days for a complete orbit (new moon - new moon)
  29. eclipses
    • solar eclipse - when the sun and moon are on the same side, moon casts a shadow on earth, only new moon
    • lunar eclipse - when the sun and moon are on opposite sides, earth casts a shado on the moon, only full moon

    • there is not an eclipse every moon cycle because the moon's orbit has a 5 degree tilt
    • saros cycle - eclipse cycle
  30. retrograde motion
    the appearance of planets moving "backward" because earth is passing them in its orbit
  31. stellar parallax
    hold thumb out and close eyes simultaneously

    how the Greeks explained retrograde motion
  32. what did ancient civilizations build to study astronomy?
    • Egyptian obelisk - determined the time of day
    • Stonehenge, Templo Mayor (Aztec), Sun Dagger - mark seasons
    • Babylonians, Mayans, Muslims - lunar calendar (Metonic cycle every 19 years, eclipse predictions)
  33. Plato
    idea of perfect circles, perfect spheres, perfect bodies
  34. Aristotle
    produced first geocentric (earth-centered model) using Plato's ideas of perfect circles
  35. Ptolemy
    created Ptolemic model, a geocentric model explaining retrograde motion using perfect circles
  36. Copernicus
    • heliocentric (sun-centered) model
    • distances in AU to planets
    • perfect circles
  37. Tycho Brahe
    • naked-eye observations
    • earth centered model
  38. Kepler
    • planets orbit in ellipse
    • three laws of planetary motion
  39. Kepler's 1st Law
    the orbit of each planet about the Sun is an ellipse with the Sun at one focus (planets distance from sun varies during its orbit)
  40. Kepler's 2nd Law
    as a planet moves around its orbit it sweeps out equal areas in equal times (planets travel faster when its closest to sun and slower when its farther)

    *think of ice skater spinning
  41. Kepler's 3rd Law
    • more distant planets orbit the sun at slower average speeds
    • p^2 = a^3
  42. Galileo
    • non-perfect bodies - Moon has craters, Venus has phases, Jupiter has moons
    • used the telescope
    • stars were too distant for stellar parallax
  43. Newton's 1st Law
    object in motion stays in motion unless acted upon by another force
  44. Newton's 2nd Law
  45. Newton's 3rd Law
    every force is paired with an equal and opposite reaction force
  46. law of conservation of angular momentum
    • total angular momentum can never change
    • m*v*r
    • spinning skater
  47. law of conservation of energy
    energy cannot appear out of nowhere and cannot disappear into nothingness
  48. gravity
    • strength of the gravitational force attracting any two objects is directly proportional to the product of their masses
    • strength of gravity between two objects between decreases with the square of the distance between their centers
    • Fg=G M1*M2/d^2
  49. orbital energy
    sum of its kinetic and gravitational potential energies
  50. gravitational encounters
    two objects can exchange orbital energy when they pass near enough so that each can feel the effects of the other's gravity
  51. atmospheric drag
    friction can cause objects to lose orbital energy
  52. escape velocity
    the speed necessary for an object to completely escape the gravity of a large body such as a moon, planet, or star
  53. tides
    • high tide is always closest to the moon
    • 4 tides per day (2 high tides and 2 low tides)
    • spring tides are highest of month (Full and New moon)
    • neap tides are lowest of the month (1st and 3rd quater moon)
  54. what is light?
    • white light is all colors mixed together
    • visible light - the light our eyes can see, ranging in wavelength from about 400 to 700 nm
    • electromagnetic radiation - another name for light of all types, from radio waves through gamma rays
    • light travels in waves and particles (photons)
  55. what are the bands of electromagnetic radiation?

    • radio band - lowest energy band; fm/am/satellite
    • infrared band - heat band; sun warmth on skin
    • visible band - band of light you see with your eyes; ROYGBIV, red = low energy, violet = high energy
    • ultraviolet band - skin cancer, cataracts, burns and tans
    • xray
    • gamma ray
  56. wave properties of light
    • the longer the wavelength the lower the frequency (vice versa)
    • wavelength x frequency = speed of light = constant