sidereal time

noun

, Astronomy.

1. time measured by the diurnal motion of stars. A sidereal day is about four minutes shorter than a solar day, with hours, minutes, and seconds all proportionally shorter.

sidereal time

noun

1. time based upon the rotation of the earth with respect to the distant stars, the sidereal day being the unit of measurement See also sidereal day

sidereal time

1. Time based on the rotation of the Earth with respect to the background of fixed stars. Astronomers generally use sidereal time rather than solar time because it is better suited to observations beyond the solar system.
2. ◆ A sidereal day is the time required for one complete rotation of the Earth on its axis with respect to a fixed star. It is an unvarying unit equal to 23 hours, 56 minutes, 4.09 seconds of solar time.
3. ◆ A sidereal month is the average period of revolution of the Moon around the Earth with respect to a fixed star, equal to 27 days, 7 hours, 43 minutes of solar time.
4. ◆ A sidereal year is the time required for one complete revolution of the Earth around the Sun with respect to a fixed star, equal to 365 days, 6 hours, 9 minutes, 9.54 seconds of solar time.
5. Compare solar time

Word History and Origins

Origin of sidereal time¹

First recorded in 1805–15

Example Sentences

But one puzzling signal showed up most days at the same sidereal time.

From Scientific American

One of its functions shows sidereal time, which is based on the amount of time it takes the Earth to make two consecutive transitions of a meridian by a fixed start.

From BBC

He described it as having everything needed “for your package tour to Mars,” including mean-solar and sidereal time, age and phase of the moon and equation of time indicators.

From New York Times

Says Kern, “The combination of solar time and sidereal time in the same watch was certainly not the idea initially, but it is a clear indication that unusual things take time.”

From Forbes

When time is calculated by the stars it is called sidereal time; when by the sun, solar, or apparent time.

From Project Gutenberg