Sidereal Days Compared To Solar Days On Other Planets
Of the eight solar planets, all but Venus and Uranus have prograde rotation—that is, they rotate more than once per year in the same direction as they orbit the sun, so the sun rises in the east. Venus and Uranus, however, have retrograde rotation. For prograde rotation, the formula relating the lengths of the sidereal and solar days is
or equivalently
On the other hand, the formula in the case of retrograde rotation is
or equivalently
All the solar planets more distant from the sun than Earth are similar to Earth in that, since they experience many rotations per revolution around the sun, there is only a small difference between the length of the sidereal day and that of the solar day—the ratio of the former to the latter never being less than Earth's ratio of .997 . But the situation is quite different for Mercury and Venus. Mercury's sidereal day is about two-thirds of its orbital period, so by the prograde formula its solar day lasts for two revolutions around the sun—three times as long as its sidereal day. Venus rotates retrograde with a sidereal day lasting about 243.0 earth-days, or about 1.08 times its orbital period of 224.7 earth-days; hence by the retrograde formula its solar day is about 116.8 earth-days, and it has about 1.9 solar days per orbital period.
By convention, rotation periods of planets are given in sidereal terms unless otherwise specified.
Read more about this topic: Sidereal Time
Famous quotes containing the words sidereal, days, compared, solar and/or planets:
“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)
“Gone are the days when my heart was young and gay,
Gone are my friends from the cotton fields away,
Gone from the earth to a better land I know,
I hear their gentle voices calling “Old Black Joe.””
—Stephen Collins Foster (1826–1864)
““Warm in December, cold in June, you say?”
“I don’t suppose the water’s changed at all.
You and I know enough to know it’s warm
Compared with cold, and cold compared with warm.
But all the fun’s in how you say a thing.””
—Robert Frost (1874–1963)
“The solar system has no anxiety about its reputation, and the credit of truth and honesty is as safe; nor have I any fear that a skeptical bias can be given by leaning hard on the sides of fate, of practical power, or of trade, which the doctrine of Faith cannot down-weigh.”
—Ralph Waldo Emerson (1803–1882)
“Why are all these dolls falling out of the sky?
Was there a father?
Or have the planets cut holes in their nets
and let our childhood out,
or are we the dolls themselves,
born but never fed?”
—Anne Sexton (1928–1974)