Hebrew calendar (astronomically called a lunar conjunction and, in Hebrew, a molad) is the moment at which the sun and moon are aligned horizontally with respect to a north-south line (technically, they have the same ecliptical longitude). The period between two new moons is a synodic month. The actual length of a synodic month varies from about 29 days 6 hours and 30 minutes (29.27 days) to about 29 days and 20 hours (29.83 days), a variation range of about 13 hours and 30 minutes. Accordingly, for convenience, a long-term average length, identical to the mean synodic month of ancient times (also
Lunar phase phases shifts by an average of almost one day for each successive month. (A lunar year lasts about 354 days.) Photographing the Moon's phase everyday for a month (starting in the evening after sunset, and repeating roughly 24 hours and 50 minutes later, and ending in the morning before sunrise) and arranging the series of photos on a calendar would create a composite image like the example calendar (May 8 – June 6, 2005) shown on the left. May 20 is blank because a picture would be taken before midnight on May 19 and the next after midnight on May