Sidereal Years to Months (yr (sid) to mo)
1 sidereal year equals 12.00045547 months (rounded).
How to convert sidereal years to months
To convert sidereal years to months, multiply the number of sidereal years by 12.00045547. The factor is rounded to 10 significant digits. To go the other way, multiply months by 0.08333017049 (rounded).
months = sidereal years × 12.00045547
Example: 10 sidereal years = 120.0045547 months.
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 year 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 Year (yr (sid))
About 365.256363 days, the time for Earth to return to the same position relative to the fixed stars.
Measured against the fixed stars, one orbit of Earth around the Sun takes about 365.256363 days, or roughly 365 days 6 hours 9 minutes 10 seconds. That is the sidereal year, and it is about 20 minutes 25 seconds longer than the mean tropical year used for the seasons.
The gap exists because of the precession of the equinoxes, which Hipparchus identified in 127 BC after comparing the two kinds of year. Ptolemy later reported his sidereal figure as about 365 days 6 hours 10 minutes, already close to the modern value. Earlier peoples had tracked the year by star events instead, such as the Egyptian watch for the rising of Sirius before the Nile flood, and Hesiod's farming advice tied to the Pleiades.
Indian astronomy kept the sidereal year in its calendars. The Surya Siddhanta gave a value near 365 days 6 hours 12 minutes 36.56 seconds, slightly long by modern measurement. NASA's fact sheet lists the sidereal orbital period of Earth as 365.256 days.
1 sidereal year = 31,558,149.76 seconds (approximately).
Sources: Wikipedia: Sidereal year; NASA Earth Fact Sheet
Month (mo)
One twelfth of an average Gregorian year: 30.436875 days. Calendar months actually range from 28 to 31 days.
Month and Moon are cognates, and the unit began as the Moon's cycle of phases, about 29.53 days from one new moon to the next. The trouble is that 12 of these fall short of a solar year, so calendars have had to choose. The Islamic calendar stays purely lunar, so its year is about 11 days shorter than the solar year, while the Hebrew calendar is lunisolar, using a 19-year cycle with an extra month. Even the start of a lunar month is still debated between observing the crescent and calculating it.
Gregorian months are a compromise that drifted far from the Moon. Their lengths run from 28 to 31 days, and this site uses their mean of 30.436875 days, one twelfth of the average year. The names also keep Roman history: September to December preserve the Latin numerals for seven to ten, since they were originally the seventh to tenth months, and Quintilis and Sextilis were renamed for Julius Caesar and Augustus. When a contract says month, check whether it means a calendar month or thirty days.
1 month = 2,629,746 seconds (exactly).
Sources: Wikipedia: Month; Wikipedia: Lunar calendar
Related conversions
- Months to sidereal years (reverse)
- Sidereal years to seconds
- Sidereal years to minutes
- Sidereal years to hours
- Sidereal years to days
- Sidereal years to weeks
- Sidereal years to years
- Seconds to months
- Minutes to months
- Hours to months
- Days to months
- Weeks to months
- Years to months
- Milliseconds to months
- Microseconds to months
- Nanoseconds to months
- Decades to months
- Centuries to months
- Millennia to months
See all time units.