Lunar calendar or crescent moons and others employing detailed calculations. Since each lunation is approximately days (29 days, 12 hours, 44 minutes, 3 seconds, or days), it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of twelve such lunations, a lunar year, is only 354 days, 8 hours, 48 minutes, 34 seconds ( days), purely lunar calendars lose around 11 days per year relative to the Gregorian calendar. In purely lunar calendars like the Islamic calendar, the lack of intercalation causes the lunar months to cycle through all the seasons of
Tranquility Calendar word tranquility is mentioned in this somewhat famous quote — "Houston, Tranquility Base Here. The Eagle Has Landed". Moon Landing Day has 20 hours, 18 minutes, and 1.2 seconds Before Tranquility and 3 hours, 41 minutes, 58.8 seconds After Tranquility. The calendar year has 13 months each with 28 days (divided in exactly 4 weeks) plus an extra day at the end of the year not belonging to any month (and so 365 days). The months are named after famous scientists: Archimedes, Brahe, Copernicus, Darwin, Einstein, Faraday, Galileo, Hippocrates, Imhotep, Jung, Kepler, Lavoisier, and Mendel. The 365th day is called