Seconds to Sidereal Days (s to d (sid))
1 second equals 0.00001160576284 sidereal days (rounded).
How to convert seconds to sidereal days
To convert seconds to sidereal days, multiply the number of seconds by 0.00001160576284. The factor is rounded to 10 significant digits. To go the other way, multiply sidereal days by 86,164.0905.
sidereal days = seconds × 0.00001160576284
Example: 10 seconds = 0.0001160576284 sidereal days.
Months and years are not constant. This site uses the average Gregorian year of 365.2425 days, so one 'year' converts to 365.2425 days, not 365; use 'common year' for exactly 365 days.
Approximate value. Standards for the sidereal day varied by place and period, so this converter uses the most commonly cited value. Treat results as estimates, not exact figures.
About these units
Second (s)
The SI base unit of time, defined by the radiation frequency of the cesium-133 atom: 9,192,631,770 cycles per second.
Our word second is a leftover of Latin. Medieval scholars divided a degree, and later the hour, into 60 parts called pars minuta prima, the first small part, and divided those again into pars minuta secunda, the second small part. NIST traces the roots further back: Babylonian and Greek astronomers split the circle into 360 degrees, and around 150 C.E. Ptolemy split each degree into 60 minutes and each minute into 60 seconds. Clocks that could show seconds appeared only in the later 16th century, and Christiaan Huygens's pendulum clock of 1656 was the first able to keep time accurately to the second.
For most of history the second was a fraction of a day, and in 1956 it was redefined as a fraction of the tropical year, a definition the SI took over in 1960. In 1967 the 13th CGPM switched to atoms: 9,192,631,770 periods of the radiation tied to a hyperfine transition of caesium-133. The 2019 SI revision restated this by fixing the caesium frequency at 9,192,631,770 hertz. NIST reports that commercial caesium clocks stay within about a three-millionth of a second per year, and experimental clocks based on other atoms are roughly ten thousand times more precise.
The second is the reference unit for time on this site.
Sources: NIST: the second and the SI redefinition; BIPM: SI Brochure, 9th edition; Wikipedia: Second
Sidereal Day (d (sid))
About 86,164.09 seconds (23 h 56 min 4 s), one rotation of the Earth relative to the stars.
Sidereal comes from the Latin word for star, and the unit measures how long Earth takes to turn once relative to the distant stars rather than to the Sun. The figure used here is about 86,164.09 seconds, or 23 hours 56 minutes 4.09 seconds. NASA's Earth fact sheet gives the same period as 23.9345 hours.
The sidereal day is about four minutes shorter than the mean solar day because Earth also moves roughly one degree along its orbit during each rotation, so it must turn slightly further before the Sun is back on the meridian. Over a year this adds up to one extra turn, giving about 366.24 sidereal days against 365.24 solar days.
For centuries astronomers measured it by timing stars as they crossed the meridian and checking observatory clocks against star catalogues. From the 1970s, radio methods such as very long baseline interferometry and pulsar timing proved more precise, and since 2003 the Earth Rotation Angle has replaced the older sidereal time conventions in formal use.
1 sidereal day = 86,164.0905 seconds (approximately).
Sources: Wikipedia: Sidereal time; NASA Earth Fact Sheet
Related conversions
- Sidereal days to seconds (reverse)
- Seconds to minutes
- Seconds to hours
- Seconds to days
- Seconds to weeks
- Seconds to months
- Seconds to years
- Seconds to milliseconds
- Seconds to microseconds
- Seconds to nanoseconds
- Seconds to decades
- Seconds to centuries
- Seconds to millennia
- Minutes to sidereal days
- Hours to sidereal days
- Days to sidereal days
- Weeks to sidereal days
- Months to sidereal days
- Years to sidereal days
See all time units.