Sidereal Days to Years (d (sid) to yr)
1 sidereal day equals 0.002730431333 years (rounded).
How to convert sidereal days to years
To convert sidereal days to years, multiply the number of sidereal days by 0.002730431333. The factor is rounded to 10 significant digits. To go the other way, multiply years by 366.242501 (rounded).
years = sidereal days × 0.002730431333
Example: 10 sidereal days = 0.02730431333 years.
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
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
Year (yr)
The average Gregorian calendar year of 365.2425 days (31,556,952 seconds). A common year has 365 days and a leap year 366.
A year is the Earth's trip around the Sun, but there are several versions. The tropical year, which tracks the seasons, is about 365.2422 days. The sidereal year, measured against the stars, is about 365.2564 days, roughly 20 minutes longer, because the Earth's axis precesses. Calendars must squeeze these into whole days, which is the origin of leap years. English year descends from Old English gear, while Latin annus, the source of annual, comes from a different root.
The Gregorian calendar, introduced by Pope Gregory XIII's bull of 24 February 1582, fixed the problem of Julian drift that had moved the March equinox away from 21 March and upset the date of Easter. Ten days were skipped, so Thursday 4 October was followed by Friday 15 October. Its rule of skipping leap days in century years not divisible by 400 gives a mean year of 365.2425 days, the value this site uses for the year. Britain and its empire switched in 1752 and Russia in 1918. Scientists write the year as a, with the Julian year fixed at 31,557,600 seconds.
1 year = 31,556,952 seconds (exactly).
Sources: Wikipedia: Year; Wikipedia: Gregorian calendar
Related conversions
- Years to sidereal days (reverse)
- Sidereal days to seconds
- Sidereal days to minutes
- Sidereal days to hours
- Sidereal days to days
- Sidereal days to weeks
- Sidereal days to months
- Seconds to years
- Minutes to years
- Hours to years
- Days to years
- Weeks to years
- Months to years
- Milliseconds to years
- Microseconds to years
- Nanoseconds to years
- Decades to years
- Centuries to years
- Millennia to years
See all time units.