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Developed pre telescopic instruments to accurately measure positions of stars and planets At age 20, he fought in a brawl and had his nose bitten off |
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1598- He moved to Prague, met Johannes Kepler 1601- He died, leaving his records of planetary positions to Kepler |
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German, inherited Brahe's records of planetary positions, realized records could be used to deduce true motions of planets around sun |
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Orbits of planets are ellipses with sun at one focus, orbits of planets are not circles or combinations of circles |
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"conic sections" can have different shapes |
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can have different shapes |
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Which scientist of the Copernican revolution was tried for heresy by the church of Rome? |
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recorded positions of fixed and wandering stars in the sky |
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What was the principle contribution of Tycho Brahe to the Copernican Revolution? |
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they are not circles nor combinations of circles |
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What is the significance of Kepler's discovery regarding the shapes of planetary orbits? |
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the ellipse is more elongated and the foci are further apart |
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higher eccentricities in ellipses mean what? |
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the ellipse is more elongated and the foci are further apart |
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higher eccentricities in ellipses mean what? |
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the average distance of planet from sun |
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How much does the sun-earth distance vary during the year? |
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as a planet orbits the sun, it sweeps out equal areas in equal times. Line between sun and planet, as the planet orbits, the line sweeps out at equal times |
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a planet moves faster when closer to the sun |
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the time a planet takes to go around the sun (its period) is related to its semi-major axis p2=a3 |
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planets more distant from the sun take longer to go around once ( they move more slowly and have larger orbits) |
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provided fundamental explanations for Kepler's laws in terms of gravitational force |
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Newtons Book, The Principia |
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describes Newtons laws of motion and law of gravitation, it completed the copernican revolution by providing fundamental explanations for Keplers laws in terms of gravitation |
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The earths orbit is elliptical, so the sun-earth distance varies by how much during the year? |
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a planet moves faster as it comes closer to the sun |
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What is the consequence of Kepler's 2nd law (the "equal areas" law)? |
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According to Kepler's 3rd law, which planet has the longest period? |
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The object will move in uniform motion |
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suppose an object is set in motion, then no further forces act upon it ( or else all forces cancel out). How will the object move? |
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motion in a straight line at a constant speed |
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car on highway, train moving at a constant speed |
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What are some examples of uniform motion? |
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any change in an objects state of motion, speeding up, slowing down, change in direction |
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gas pedal, breaks, steering wheel |
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what control devices in a car can cause an acceleration? |
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NO! if an object is experiencing acceleration it cannot be in uniform motion |
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Can an object experiencing acceleration also be in uniform motion? |
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miles per hour, kilometer per hour, meters per second |
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What are some units of velocity? |
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cyclist moving along a straight path at a constant speed |
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Which example below illustrates uniform motion? |
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cyclist moving along a straight path at a constant speed |
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In which case below can we conclude that no acceleration is occurring? |
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what unit is not a unit of velocity or speed? |
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forces have a strength and a direction |
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the combined effect of all forces |
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net force is in direction of motion, train speeds up (acceleration) |
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what if the force exerted by the engine exceeds the force of friction? |
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train slows down ( acceleration) |
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What if the force exerted by the engine is less than the force of friction? |
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train wreck! train plunges through rail |
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What if the upward force exerted by the rail is less than the downward force of gravity? |
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Suppose an object is falling downward, at 50 m/s, how fast after 4 seconds? |
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Consider the 4 forces acting upon a train, what force is directed vertically upward? |
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Imagine sitting in a chair. If the force of gravity is greater than the upward force exerted on you by the chair, what will happen? |
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Newtons 1st law of motion |
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if no net force acts on an object, the object remains i uniform motion (or at rest) experiences no acceleration |
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Newtons 2nd law of motion |
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if a net force acts on an object, the object experiences acceleration where A=Fnet/ M |
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high force on an object (powerful engine) low mass (light weight) |
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what characteristic should a car have in order to achieve highest possible forward acceleration? |
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suppose a force of 20 newtons is applied to an object having a mass of 5 kilograms. What is the acceleration? |
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force of 10 newtons on mass of 1 kilogram |
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what circumstances will lead to the highest acceleration? |
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Toward the sun, perpendicular to the motion of the planet |
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consider a hypothetical planet in a circular orbit around the sun. In what direction does the fore acting on this planet point? |
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a measure of resistance of an object to being put into motion, measure of inertia of an object . measured in kilograms and grams, the same everywhere |
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the gravitational force exerted on an object, can very with location ( earth vs. moon). units in newton and pound |
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Mass=same, Weight = 1/6th |
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Consider a bowling alley on the moon, would masses of balls and pins be same as on earth? the weights? |
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meters per second (m/sec) |
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What is the metric unit for speed or velocity? |
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meters per second per second (m/sec2) |
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what is the metric unit for acceleration? |
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olympic diver who has just left the springboard |
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Which person experiences weightlessness? |
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the 2 forces are equal in strength |
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How does the gravitational force exerted by the Earth upon the sun compare to the sun's force on earth? |
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Newtons 3rd law of motion |
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If one object exerts a force on a second object the second object exerts equal opposite force |
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friction force from the sidewalk exerts upon your feet |
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What force pushes you forward as you take off from a stand still on a sidewalk? |
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the earth isnt in uniform motion about the sun (1st law) |
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Why must a net force be acting upon earth? |
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the sun exerts force on planets, just as earth exerts force on objects near it |
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mass 1 and mass 2, distance between centers r |
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what determines strength of gravitational force between two objects? |
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how does force m1 exerts on m2 compare with force that m2 exerts on m1? |
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the 10 kg feels 10x force |
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Which object feels stronger force of gravity from earth? |
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which object accelerates faster? (neglecting air resistance) |
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If the masses of two objects are each doubled, the gravitational force between them will |
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if the distance between 2 objects increases 3 times, the gravitational force between them will... |
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the acceleration a 10kg object experiences when dropped is ? the acceleration of a 1000kg object |
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location of sunrise on horizon |
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how does the location of sunrise (sunset) on the horizon change over the year? |
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about march 21 and september 21 (equinox) |
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When does the sun rise due east? |
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June 21 (summer solstice date) |
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When does the sun rise as far north east as possible? |
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Dec 21 (winter solstice date) |
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When does the sun rise as far southeast as possible? |
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When is the sun angle highest? |
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when is the sun angle the lowest? |
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How many sunlit hours on june 21 |
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how man sunlit hours on mar/sep 21? |
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how many sunlit hours on dec 21? |
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sunlight more direct in the summer, and there is more sunlight per day |
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why is it warmer in summer than winter? |
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they are reversed, mid summer in australia is dec 21 |
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how do seasons in the southern hemisphere compare with those in the north? |
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very little, earth closest to the sun in early january, furthest in early july |
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what effect does the varying earth-sun distance have on the seasons? |
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23.5% tilt of earths axis |
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what is there about the earth that causes seasons? |
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day of year when days are longer or shorter, they occur june 21 and dec 21 |
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date of year with 12 hours of daylight and darkness |
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lexington= 15-19 1/2 hours equator= hours all year Alaska= 6-18 hours above arctic circle= 24 hours |
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is the seasonal variation different at different latitudes on earth? |
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the 23 1/2 tilt of the earths axis relative to its orbit |
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the cause of the seasons on earth is? |
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upon what date would you expect no sunlight at all near the earths south pole? |
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On approx. what date does the spring equinox fall in cape town south africa? |
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celestial objects move in circles at constant angles above horizone |
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what is daily apparent motion of celestial objects as viewed from the north pole? |
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all parts of earth would get 12 hours of sunlight pre day all year long |
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if earths axis were perpendicular to its orbit (not 23 1/2) how would seasons be different? |
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45 degrees above the north horizonw |
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Imagine a star viewed near the earth's north pole, 45 degrees above the south horizon. Approx. where will the same star be 12 hours later? |
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about 23 degrees below the horizon |
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At the earths south pole, where will the sun be in late june? |
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suppose the earths axis had no tilt ( that is, its axis were perpendicular to its orbits). In this case, about how many hours of sunlight would residents of anchorage alaska experience on dec 21? |
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how long does it take to complete a cycle of motion? |
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how long does the cycle of lunar phase take? |
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wanting gibbous, full moon, new moon, wanting crescent, 1st and 3rd quarter |
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what are some names of phases of the moon? |
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1/2 of the illuminated hemisphere |
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what fraction of moons surface is illuminated by sun at any given moment |
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in what direction does moons illuminated hemisphere always face the earth? |
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no, as the moon orbits earth, different fractions of moons illuminated face earth |
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does the moons illuminated hemisphere always face the earth? |
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at what lunar phase does none of moons illuminated hemisphere face earth? |
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1st quarter and 3rd quarter |
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at what lunar phases does half moons illuminated hemisphere face earth? |
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at what lunar phases does the illuminated hemisphere of the moon point both toward the sun and the earth? |
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the period of time between new moon and full moon is? |
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about what fraction of the moons surface is illuminated by the sun at 1st and 3rd quarters? |
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shadows of earth on moon (causes lunar eclipses occasionally |
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what does not cause phases of the moon? |
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0 degrees during new moon |
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90 degrees sun moon angle |
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180 degrees sun moon angle |
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90 degrees sun moon angle |
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early evening, full moon in opposite of direction of the sun, full moon rises when sun sets |
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at what time of day does the full moon rise? |
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rises at the same time as the sun |
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at what time of day does the new moon rise? |
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near 1st quarter in the afternoon, near 3rd quarter in morning |
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when can you see the moon during the daytime? |
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yes, every observer on earth sees the same phase of the moon at a given moment |
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if moon is full in lexington tonight is it also full tonight in santiago chili? |
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does earth show phases when viewed from the moon? |
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If the moon sets at sunset, what is the phase of the moon? |
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if the moon is full, what is the angle between the moon and the sun in the sky? |
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suppose you see the moon setting in early evening shortly after sunset. what is the phase of the moon? |
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phases of earth seen from the moon are always opposite of phases of the moon seen from the earth |
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yes, when the moon is a thin crescent |
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can we ever see the dark side of the moon? |
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earth nearly full, very bright in the sky |
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what is the phase of earth as seen on the moon? |
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we see dark side of the moon because of reflected light from the earth |
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does same hemisphere of the moon always face earth as moon orbits earth? |
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yes, to keep same face pointed at earth, moon must rotate exactly once with every orbit |
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does the moon rotate on its axis at all? |
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earth remains motionless in lunar sky |
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consequences of synchronous rotation |
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how long is a day on the moon? |
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