Synodic Months to Days (mo (syn) to d)
1 synodic month equals 29.53059 days exactly.
How to convert synodic months to days
To convert synodic months to days, multiply the number of synodic months by 29.53059. This factor is exact. To go the other way, multiply days by 0.03386319068 (rounded).
days = synodic months × 29.53059
Example: 10 synodic months = 295.3059 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 synodic month varied by place and period, so this converter uses the most commonly cited value. Treat results as estimates, not exact figures.
About these units
Synodic Month (mo (syn))
About 29.53 days, the time from one new moon to the next. The basis of lunar and many religious calendars.
A synodic month is the span from one new moon to the next, when the Moon returns to the same position relative to the Sun as seen from Earth. Its mean length is about 29.53 days, or 29 days 12 hours 44 minutes 3 seconds. The word synodic derives from a Greek term for meeting, since the Sun and Moon meet in the sky at each new moon.
Individual months are far from equal. Because the Moon's orbit is elliptical and the Sun perturbs it, a single lunation can run from about 29.27 to about 29.83 days, and in a given year the interval can differ from the mean by up to roughly seven hours. In 2001, for instance, lunations ranged from 29 days 19 hours in January to 29 days 7 hours in July.
Babylonian astronomers were the first to recognise this kind of month and to work out its mean length, and the quantity still underlies lunar and lunisolar calendars such as the Islamic, Hebrew and Chinese ones. It is longer than the sidereal month of about 27.3 days because Earth moves along its orbit while the Moon circles it.
1 synodic month = 2,551,442.976 seconds (approximately).
Sources: Wikipedia: Lunar month
Day (d)
24 hours or 86,400 seconds. The mean solar day; the actual rotation of the Earth is about 4 minutes shorter (see sidereal day).
Old English dæg is the root of our day, with close cousins in German Tag, Dutch dag and Icelandic dagur, all descending from Proto-Germanic dagaz. It is the oldest unit here, because the cycle of light and dark needs no instrument. Yet the day we count is a constructed average: the actual interval from one noon to the next varies through the year by up to about 7.9 seconds, because Earth's orbit is elliptical and its axis is tilted.
Astronomers smooth this out with a fictitious mean Sun, giving the mean solar day, and the day in the SI sense is fixed at exactly 86,400 seconds. Reality has drifted slightly: the mean solar day has recently averaged about 86,400.002 seconds, and tidal drag from the Moon is lengthening it by about 2 milliseconds per century. That is why 27 leap seconds were added to UTC between 1972 and 2022. One rotation measured against the distant stars is shorter, about 23 hours 56 minutes 4.09 seconds, and a year contains one more of these sidereal days than solar days.
1 day = 86,400 seconds (exactly).
Sources: Wikipedia: Day; BIPM: SI Brochure, 9th edition
Related conversions
- Days to synodic months (reverse)
- Synodic months to seconds
- Synodic months to minutes
- Synodic months to hours
- Synodic months to weeks
- Synodic months to months
- Synodic months to years
- Seconds to days
- Minutes to days
- Hours to days
- Weeks to days
- Months to days
- Years to days
- Milliseconds to days
- Microseconds to days
- Nanoseconds to days
- Decades to days
- Centuries to days
- Millennia to days
See all time units.