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When the moon is at its first or last quarter the

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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 _________ tides. Explanation: Neap. The neap tides are lower than usual on the Earth. The Earth is not perfectly spherical and its equatorial diameter is twenty-seven miles greater than its _________ diameter. n: Polar. A perfect sphere would have the same diameter at all points.
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_______________ 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. Explanation: Precession. The Earth's rotation axis is not fixed in space; it is moving like the top of a wobbly top as illustrated by the animation below. Of course by human standards, this conical motion is imperceptible--with a precession period of 26,000 years, it takes 26,000 years for the Earth's axis to do a full rotation. Another way to look at this is that right now the North Star is Polaris, but in 13,000 years the star Vega will be approximately at the North Celestial Pole. Then in 26,000 years, the pole will be pointing in the same direction again--back at Polaris. The twenty brightest stars as seen from Earth are classified in that manner because they have high ______________ and/or are nearby. Explanation: Luminosity. Those stars are: Sun, Sirius, Canopus, Arcturus, Alpha Centauri, Vega, Rigel, Procyon, Achernar, Betelgeuse, Hadar (Agena), Capella A, Altair, Aldebaran, Capella B, Spica, Antares, Pollux, Fomalhaut, and Deneb. Note that many people mistakenly think that Polaris, the North Star, is the brightest star in the sky, when it's actually #48 on the list. Sirius is the brightest star after the sun.
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A visual grouping of five galaxies of which four form the first compact galaxy group ever discovered is called the ______________ ______________. Explanation: Stephan's Quintet. This group was discovered by Edouard Stephan in 1877 and is one of the most studied of all the compact galaxy groups. The length 206,265 AU (astronomical units) is defined as a _____________. Explanation: Parsec. A parsec is 206,265 AU, which is about 30 trillion kilometers (19 trillion miles) or 3.262 light years. The name parsec stands for "parallax of one second of arc" and the concept is based on trigonometry. A parsec is too big of a unit to use within our solar system, which is only around 1/2600th of a parsec across. Typically you would describe the distance between nearby stars in parsecs, kiloparsecs for the distance between parts of a galaxy or within galaxy groups, and megaparsecs for distances between galaxy clusters. _____________ is the change of angular position of two observations of a single object relative to each other as seen by an observer, caused by the motion of the observer. Explanation: Parallax. This is the apparent shift of an object against the background that is caused when the observer changes positions. When standing in one place it looks one way; if the observer moves, the background changes and the object looks different.
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The below graphic shows a simple demonstration of how the same star would look different when the Earth is in two different parts of its orbit around the sun:
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