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Study Guide SOL 4.7
The Sun, Moon and Earth
Revolution or Rotation?
Rotation and Revolution: The Earth completes one revolution (or orbit)
around the sun every year (365 days). The Earth completes one rotation on
its axis every 24 hours. Day and night are caused by the Earth's rotation on
its axis.
The Seasons and the Earth's Tilt
• Earth's tilt causes seasons: The Earth is tilted on its axis as it revolves
around the sun. The hemisphere tilted toward the sun receives the sun's
rays more directly and therefore has warmer temperatures as well as longer
days (summer), while the half of the Earth tilted away has cooler
temperatures and shorter days (winter). It's important to realize that
warmer summer temperatures occur because the Sun's rays are striking
more directly, not because part of the Earth is closer to the Sun.
The Phases of the Moon
• The moon revolves around the Earth about once every month. The phases
of the moon are caused by its position relative to the Earth and the sun. (we
see only part of the sunlit side of the moon) The phases of the moon include
the new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous,
last quarter, and waning crescent.
The Sun, the Moon and the Planets
• The sun is an average-sized yellow star, about 110 times the diameter of
the Earth. The sun is approximately 4.6 billion years old.
• Our moon is a small rocky satellite, having about one-quarter the diameter
of the Earth and one eightieth its mass. It has extremes of temperature,
(virtually) no atmosphere, no water, and no life.
• The Earth is one of nine planets that revolve around the Sun and comprise
the solar system. The Earth, third planet from the sun, is one of the four
rocky inner planets. It is about 150 million kilometers from the sun.
• The Earth is a geologically active planet with a surface that is constantly
changing. Unlike the other four inner planets, it has large amounts of lifesupporting water and an oxygen-rich atmosphere. The Earth’s protective
atmosphere blocks out most of the sun’s damaging rays.
Aristotle, Ptolemy, Copernicus and Galileo
• Our understanding of the solar system has changed from an Earthcentered model (Aristotle and Ptolemy) to the sun-centered model
(Copernicus and Galileo).
• The NASA Apollo missions added a great deal to our understanding of the
moon.
• Our understanding of the sun, moon, and the solar system continues to
change with new scientific discoveries.