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53 Cards in this Set
- Front
- Back
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What direction does the Earth turn around its axis of rotation?
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West to East
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What direction do we perceive the Earth turning?
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East to West
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What is the Celestial Sphere?
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A convenient way to think about the sky; how sky appears to rotate around the Earth. Fictional giant sphere around Earth.
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What are the two points that the celestial sphere seems to turn around?
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North celestial pole (NCP) and South celestial pole (SCP)
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How do we define the horizon for a person at any point on the Earth?
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the plane under your feet that just touches the earth where you are standing
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What would the horizon for someone standing at the north pole?
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Celestial Equator
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How do stars appear to move around the sky at the north pole?
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Make circles around the sky; staying the same height above the horizon
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How do stars appear to rise and set for someone standing at the equator?
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Stars will rise in East and set in West
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For someone living in Mt. P where would you find the North Celestial Pole?
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look up
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How do stars near the North Celestial Pole turn around the pole: clockwise or counterclockwise?
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Counterclockwise
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Why do we have seasons?
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Because of the 23.5 degree tilt.
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What is the tilt of the Earth's rotation axis relative to a line perpendicular to the Ecliptic?
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23.5 degrees
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When it is summer in the northern hemisphere, what season is it in the southern hemisphere?
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Winter
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What are the 4 special days of the year: summer solstice, winter solstice, autumnal equinox, vernal equinox?
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Summer: June 21st; Winter: December 21st; Autumnal: Sept. 21st; March: 21st.
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What two dates would the sun appear to be on the celestial equator? How many hours of daylight will we have at each?
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The vernal and autumnal equinoxes; approximately 12 hours.
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Where will the sun appear to rise and set on the summer solstice?
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look up
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Why do the constellations that we see in the night sky change with the seasons?
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look up
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What is the precession of the Earth's rotation axis?
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A gradual wobble that changes the orientation of Earth's axis in space.
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What causes precession?
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The gravity of the sun and moon pulls on the bulge at the equator.
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Toward what star does the north pole of the Earth's rotation axis point right now?
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Polaris
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Where will the pole point in 13,000 years?
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Towards the south; The new north pole will be Vega.
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When will the north celestial pole return to its present location?
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26,000 years
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Will the summer constellations of today appear as winter constellations in 13,000 years?
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Yes
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What is a tropical year? Will June always be a summer month?
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The time for the sun to go from the vernal equinox on one year to the vernal equinox on the next year; yes it will.
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Why does the moon go through phases?
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We see phases for the moon because as the moon orbits Earth we see varying amounts of the sunlit side.
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Memorize the phases
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Of the moon!
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What is the "umbra"? What is the "penumbra"?
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Umbra: sun is completely blocked from view.
Penumbra: sun is Partially blocked from view. |
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What would you see in each region of the umbra and penumbra?
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You would see that the moon is in front of the sun and smaller than the sun.
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What would you see in the region behind the umbra?
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A ring of sunlight behind the moon; corona
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What is the difference between a total solar eclipse and an annular solar eclipse?
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Total Solar Eclipse: moon is closer to earth; happens at a new moon phase; you will see a diamond ring effect. There is no sunlight.
Annular Solar eclipse: moon is farther away from the earth; moon is smaller than the sun so you will see a disk of sun; disk that you see is called the annulus. |
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Why does the umbra of the moon's shadow reach the surface of the Earth sometimes and not others?
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look up
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What would you see during each type of solar eclipse if you were directly along the path of the eclipse?
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Total: Corona
Annular: Annulus |
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How does a lunar eclipse occur?
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They happen at the full moon phase; it occurs when the earth, sun and moon are all lined up
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Difference between a total lunar eclipse and a partial lunar eclipse?
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Total: The moon will have a red glow
Partial: The moon will look like it has a chunk taken out of it. |
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Why does the moon have a red color during a total lunar eclipse?
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Because the earth has a thin atmosphere, when sunlight passes through it and into the umbra and onto the moon
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What phases of the moon do solar and lunar eclipses occur?
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The full moon phase
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Why don't solar and lunar eclipse occur every month?
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Because most of the time the moon, sun and earth are not lined up because of a 5 degree tilt.
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What direction across the sky do planets appear to move over months and years?
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East to West
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What is retrograde motion?
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When planets appear to move backwards because Earth is traveling faster
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What is a deferent? What is the epicycle?
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The ring that the planets go around the Earth; the epicycle is the little loops the planets appear to make along the deferent
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According to Ptolemy, what was special about the orbits of Mercury and Venus?
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He proposed that Mercury and Venus were on an epicycle path tuck on an imaginary line between the Earth and Sun.
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In the Heliocentric theory of Copernicus, what was at the center of the solar system? What did he assume about the shape of planet's orbits?
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Sun; he assumed that an inner planet moves faster than an outer planet
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How do we explain retrograde motion according to Copernicus' view?
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Like passing a car on the freeway
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How did Galileo use observations of Venus to prove that Copernicus was right?
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By seeing all possible phases for Venus
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Who was Tycho Brahe and what did he do?
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Rich guy who built the observatory; made accurate measurements of the positions of planets over 20 years
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Who was Johannes Kepler?
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Created three laws of planetary motion
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What are the 3 laws of planetary motion? What is another name for Kepler's laws?
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1) The orbits of the planets are ellipses and the sun is at one side of the ellipse
2) "Law of Areas" A line from the sun to the planet sweeps out equal areas in equal times 3) The orbital period (in years) squared equals the average distance from the sun (in AU) cubed These are called Empirical Laws. |
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Where is the sun located in a planet's orbit?
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To one side of the ellipse; the other side of the ellipse is nothing special
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What is the ellipses eccentricity scale?
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(0-1) 0 being a circle, .9 being a pretty normal ellipse and 1 being an infinite parabola
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What units should we use for the orbital period and the distance from the sun?
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Astronomical Units
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How does the avg. distance of the planet from the sun (a) relate to its orbital period (P) around the sun?
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(law 3) P^2 = a^3
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An astronomical unit is?
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The average distance from the Earth to the sun
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Empirical laws are?
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Known from repeated observation; not known why
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