Lunar month circular, the speed of Earth's progression around the Sun varies during the year. Thus, the angular rate is faster nearer periapsis and slower near apoapsis. The same is so for the Moon's orbit around the Earth. Because of these variations in angular rate, the actual time between lunations may vary from about 29.18 to about 29.93 days. The long-term average duration is days (29 d 12 h 44 min 2.8016 s). The synodic month is used to calculate eclipse cycles. It is customary to specify positions of celestial bodies with respect to the vernal equinox. Because of Earth's precession of
April 2015 lunar eclipse April 2015 lunar eclipse A total lunar eclipse took place on 4 April 2015. It is the former of two total lunar eclipses in 2015, and the third in a "tetrad" (four total lunar eclipses in series). Other eclipses in the tetrad are those of 15 April 2014, 8 October 2014, and 28 September 2015. This is the 30th member of Lunar Saros 132, and the first total eclipse. The previous event was the March 1997 lunar eclipse, being slightly partial. Totality lasted only 4 minutes and 44 seconds, making it the shortest lunar totality in almost five centuries since