Lunar calendar traces of its origin in the earlier lunar calendar, which continued to be used alongside it for religious and agricultural purposes. Present-day lunisolar calendars include the Chinese, Hindu, and Thai calendars. Synodic months are 29 or 30 days in length, making a lunar year of 12 months about 11 days shorter than a solar year. Some lunar calendars do not use intercalation, such as most Islamic calendars. For those that do, such as the Hebrew calendar, the most common form of intercalation is to add an additional month every second or third year. Some lunisolar calendars are also calibrated by
Apollo 8 lines took place on December 18, three days before the scheduled launch. As the first manned spacecraft to orbit more than one celestial body, Apollo 8's profile had two different sets of orbital parameters, separated by a translunar injection maneuver. Apollo lunar missions would begin with a nominal circular Earth parking orbit. Apollo 8 was launched into an initial orbit with an apogee of and a perigee of , with an inclination of 32.51° to the Equator, and an orbital period of 88.19 minutes. Propellant venting increased the apogee by over the 2 hours, 44 minutes, and 30 seconds spent