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Sidereal Day




An apparent sidereal day is the time it takes for the s, 56 Minute s, 4.091 seconds).

The reason there is one more sidereal day than "normal" days in a year is that the Earth's orbit around the Sun offsets one sidereal day, giving observers on Earth 365 1/4 days, even though the planet itself rotated 366 1/4 times (the Earth rotates in the same direction around its axis as it does around the Sun: seen from the northern sky, counter-clockwise).

Midnight , in Sidereal Time , is when the First Point Of Aries crosses the upper meridian.

A mean sidereal day is reckoned, not from the actual transit, but from the transit of the mean vernal equinox (see: Mean Sun ).


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