Why do the solar and sidereal day differ?
Try this: Place a cent and quarter face up on the table before you, with the penny on the left. Abe and George will be facing each other. The penny represents earth and the quarter the sun. Abe is our observer on the earth; he sees the sun directly in front of him. Move the penny around the quarter in a clockwise direction. When the penny is above the quarter, the quarter passes out of Abe’s view and remains hidden until it appears overhead when the penny is below the quarter. The sun has risen and set, but the penny hasn’t rotated at all; Abe has continued to look at the same point on the wall all this time. In other words, the number of sidereal days in a year is one more than the number of solar days. Because the vernal equinox itself moves (due to the precession of the Earth’s axis), the sidereal day is not quite the same as the period of earth’s rotation with respect to a fixed direction in space. That period is 0.0084 seconds longer than a sidereal day. Oddly enough, this, the tr
