Julian Years to Seconds (a to s)
1 Julian year equals 31,557,600 seconds exactly.
How to convert Julian years to seconds
To convert Julian years to seconds, multiply the number of Julian years by 31,557,600. This factor is exact. To go the other way, multiply seconds by 3.168808781×10⁻⁸ (rounded).
seconds = Julian years × 31,557,600
Example: 10 Julian years = 315,576,000 seconds.
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.
About these units
Julian Year (a)
Exactly 365.25 days (31,557,600 seconds). The astronomical standard; a light-year is defined using it.
Astronomers wanted a year that would never change, so they borrowed the average length of the old Julian calendar year: exactly 365.25 days of 86,400 SI seconds, or 31,557,600 seconds. The symbol is a, or aj when it must be told apart from other years. It is not an SI unit, but the IAU lists it among the non-SI units accepted for use in astronomy.
The mean tropical year drifts slightly from one year to the next, so it makes a poor unit, whereas the Julian year is constant because it rests on the SI second. It still approximates both the sidereal and tropical years to within about 0.008 days. The current standard epoch, J2000.0, is exactly 12:00 TT on 1 January 2000, and other Julian epochs are counted in Julian years from it. The light-year is defined as the distance light covers in one Julian year.
1 Julian year = 31,557,600 seconds (exactly).
Sources: Wikipedia: Julian year (astronomy); Wikipedia: Light-second; NIST SP 811 Appendix B.8: factors for units outside the SI
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
Related conversions
- Seconds to Julian years (reverse)
- Julian years to minutes
- Julian years to hours
- Julian years to days
- Julian years to weeks
- Julian years to months
- Julian years to years
- Minutes to seconds
- Hours to seconds
- Days to seconds
- Weeks to seconds
- Months to seconds
- Years to seconds
- Milliseconds to seconds
- Microseconds to seconds
- Nanoseconds to seconds
- Decades to seconds
- Centuries to seconds
- Millennia to seconds
See all time units.