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  • Why is there day and night? - NASA
    Clearly, when you see the Sun shining in the sky, it is day, and when you don't it is night So the real question is "why is the Sun in the sky at some times and not at others?" We can see that the Sun seems to move across the sky starting in the east in the morning, moving toward the south at noon, and then toward the west as the day ends
  • Why is space black? - NASA
    The blue color of the sky is a result of this scattering process At night, when that part of Earth is facing away from the Sun, space looks black because there is no nearby bright source of light, like the Sun, to be scattered If you were on the Moon, which has no atmosphere, the sky would be black both night and day
  • StarChild Question of the Month for November 1998 - NASA
    The gibbous moon appears to grow fatter each night until we see the full sunlit face of the Moon We call this phase the full moon It rises almost exactly as the Sun sets and sets just as the Sun rises the next day The Moon has now completed one half of the lunar month During the second half of the lunar month, the Moon grows thinner each night
  • Why is Polaris the North Star? - NASA
    The Earth bulges out at its equator, and the gravitational attraction of the Moon and Sun on the bulge provided the "nudge" which made the Earth precess It was the ancient Greek astronomer and mathematician Hipparchus who first estimated the precession of the Earth's axis around 130 B C The period of precession is about 26,000 years
  • StarChild: Facts about Ceres - NASA
    Average Solar Distance : 415 million km; Revolution Period : 4 6 Earth years; Rotation Period : 9 074 hours
  • A Song for All Seasons - NASA
    Look at the chart of the Earth's orbit around the Sun above and the position (1, 2, 3, or 4) which you believe is where the Earth would be in its orbit during that season you hear The Earth's tilt remains at a constant 23 5 degrees, but you must decide (depending on the season) if the northern hemisphere is tilted toward or away from the Sun
  • What causes a falling star? - NASA
    At certain times of year, you are likely to see a great number of meteors in the night sky These events are called meteor showers and they occur when the Earth passes through the trail of debris left by a comet as it orbits the Sun These showers are given names based on the constellation present in the sky from which they appear to originate
  • Galileo Galilei - NASA
    The Catholic Church, which was very powerful and influential in Galileo's day, strongly supported the theory of a geocentric, or Earth-centered, universe After Galileo began publishing papers about his astronomy discoveries and his belief in a heliocentric , or Sun-centered, Universe, he was called to Rome to answer charges brought against him
  • StarChild: Cosmology - NASA
    He thought Earth was the center of the universe and that the Sun, Moon, planets, and all the fixed stars revolved around it Aristotle's ideas were widely accepted by the Greeks of his time The exception, a century later, was Aristarchus, one of the earliest believers in a heliocentric or sun-centered universe
  • StarChild: Cosmology - NASA
    The ancient Greeks believed that the Sun, Moon, and planets circled the Earth To explain the fact that planets sometimes appear to travel backward in the sky, the Greeks thought each moved in a small circle (called an epicycle) that was itself orbiting Earth Ptolemy summarized the theory in the Almagest, written in the 140 AD This view of





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