DSST Astronomy notes 1

Ai3b for the first fifteen minutes or so these

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(a.i.3.b) For the first fifteen minutes or so, these particles underwent nuclear fusion, forming light elements such as helium and hydrogen (a specific type of hydrogen called deuterium).
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(a.i.3.c) The idea is that there were only a few minutes for these reactions to occur because the universe was expanding rapidly--temperature and density were dropping. So, there was no opportunity for heavier elements to form. (a.i.3.d) Therefore, the universe should consist almost entirely of light elements. Investigation shows that indeed, the older an object is in space, the less heavy elements it contains, but even really old objects contain at least 25% helium. (a.i.3.e) The gist is, the abundance of light elements such as Helium (almost 25% of matter in the universe) and Hydrogen (about 3/4 of all matter) is seen as one of the big three pieces of evidence to support the Big Bang theory 161) The gravitational attraction of the moon and sun, acting on the Earth, has two consequences that arise because the Earth is not a perfect Sphere but rather an ablate spheroid. (a.i.1.a) Since the Earth is not exactly spherical, its curvature varies with location. 162) The shape of the Earth and the Gravitational pull of the moon and the sun cause two phenomena: a.i) Tides and precession. a.ii) The differential gravitational forces of the moon's attraction on different parts of the Earth with respect to its center are called tidal forces. (a.ii.1.a) The areas of the Earth facing the moon have a higher gravitational pull than those away from the moon. This pull causes the Earth to slightly distort, rising up and down and tilting as a fluid surface, causing the sea level changes. 163) The sun also produces tides on the Earth, although it is less than half as effective a tide-raising agent as the moon. a) Actually, the gravitational attraction between the sun and the Earth is about 150 times as great as that between the Earth and the moon. a.i) However, the sun is so distant that it attracts all parts of the Earth with almost equal strength. a.ii) The moon is close enough for its attraction on the near side of the Earth to be substantially greater. 164) When the sun and moon are lined up (at a full moon), the tides produced are greater than normal and these are called spring tides. a) The spring tides are the highest tides that the Earth experiences. b) Of these high tides, the highest occur at those times during a full moon when the moon is closest to the center of the Earth. 165) When the moon is at its first or last quarter, the tides produced by the sun partially cancel out the tides of the moon and these are called Neap tides. a) The neap tides are lower than usual on the Earth. 166) The Earth is not perfectly spherical and its equatorial diameter is twenty-seven miles greater than its Polar diameter. a) A perfect sphere would have the same diameter at all points. 167) Precession is a slow, conical motion of the Earth's axis of rotation caused by the gravitational torque of the moon and the sun on the Earth's equatorial bulge. a)
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ai3b For the first fifteen minutes or so these particles...

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