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
April 2015 lunar eclipse 17 October 1529 (which lasted 1 minute and 42 seconds). Another shortest occurs on December 28 1917, lasting (11 minutes and 58 seconds). The next very short lunar totality will occur on 26 May 2021 (which will last 14 minutes and 24 seconds). This was the sixth total lunar eclipse out of nine with totality under 5 minutes in a five millennium period between 2,000 BC and 3,000 AD. However, due to the oblateness of the Earth, this lunar eclipse may have actually been (barely) a partial eclipse. This eclipsed moon was 12.9% smaller in apparent diameter than the supermoon