Molad based on a constant interval cycle that is widely but incorrectly regarded as an approximation of the time in Jerusalem of the mean lunar conjunction. Each "molad" moment occurs exactly 29 days 12 hours 44 minutes and 3+/ seconds (or, equivalently, 29 days 12 hours and 44+/ minutes) after the previous "molad" moment. This interval is numerically exactly the same as the length of the mean synodic month that was published by Ptolemy in the Almagest, who cited Hipparchus as its source. Although in the era of Hipparchus (2nd century BC) this interval was equal to the average time between
Lunar month month because it is the cycle of the visible phases of the Moon. Most of the following types of lunar month, except the distinction between the sidereal and tropical months, were first recognized in Babylonian lunar astronomy. The period of the Moon's orbit as defined with respect to the celestial sphere of apparently fixed stars (nowadays the International Celestial Reference Frame (ICRF)) is known as a sidereal month because it is the time it takes the Moon to return to a similar position among the stars (): days (27 d 7 h 43 min 11.6 s). This type of month