Sidereal Time and Solar Time
Solar time is measured by the apparent diurnal motion of the sun, and local noon in solar time is the moment when the sun is at its highest point in the sky (exactly due south or north depending on the observer's latitude and the season). The average time for the sun to return to its highest point is 24 hours.
The Earth makes a rotation around its axis in a sidereal day; during that time it moves a short distance (about 1°) along its orbit around the sun. So after a sidereal day has passed the Earth still needs to rotate a bit more before the sun reaches its highest point. A solar day is, therefore, nearly 4 minutes longer than a sidereal day.
The stars are so far away that the Earth's movement along its orbit makes nearly no difference to their apparent direction (see, however, parallax), and so they return to their highest point in a sidereal day.
Another way to see this difference is to notice that, relative to the stars, the Sun appears to move around the Earth once per year. Therefore, there is one fewer solar day per year than there are sidereal days. This makes a sidereal day approximately 365.24⁄366.24 times the length of the 24-hour solar day, giving approximately 23 hours, 56 minutes, 4.1 seconds (86,164.1 seconds).
Read more about this topic: Sidereal Time
Famous quotes containing the words sidereal, time and/or solar:
“Perhaps our eyes are merely a blank film which is taken from us after our deaths to be developed elsewhere and screened as our life story in some infernal cinema or despatched as microfilm into the sidereal void.”
—Jean Baudrillard (b. 1929)
“English people apparently queue up as a sort of hobby. A family man might pass a mild autumn evening by taking the wife and kids to stand in the cinema queue for a while and then leading them over for a few minutes in the sweetshop queue and then, as a special treat for the kids, saying “Perhaps we’ve time to have a look at the Number Thirty-One bus queue before we turn in.””
—Calvin Trillin (b. 1940)
“Senta: These boats, sir, what are they for?
Hamar: They are solar boats for Pharaoh to use after his death. They’re the means by which Pharaoh will journey across the skies with the sun, with the god Horus. Each day they will sail from east to west, and each night Pharaoh will return to the east by the river which runs underneath the earth.”
—William Faulkner (1897–1962)