Total lunar eclipse on April 13, 1968
A total lunar eclipse occurred at the Moon’s descending node of orbit on Saturday, April 13, 1968, with an umbral magnitude of 1.1116. A lunar eclipse occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. A total lunar eclipse occurs when the Moon's near side entirely passes into the Earth's umbral shadow. Unlike a solar eclipse, which can only be viewed from a relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of Earth. A total lunar eclipse can last up to nearly two hours, while a total solar eclipse lasts only a few minutes at any given place, because the Moon's shadow is smaller. Occurring about 1.1 days before perigee (on April 14, 1968, at 7:50 UTC), the Moon's apparent diameter was larger.
This lunar eclipse was the third of a tetrad, with four total lunar eclipses in series, the others being on April 24, 1967; October 18, 1967; and October 6, 1968.
Visibility.
The eclipse was completely visible over much of North America and South America, seen rising over northwestern North America and the central Pacific Ocean and setting over Europe, Africa, and the Middle East.
Eclipse details.
Shown below is a table displaying details about this particular solar eclipse. It describes various parameters pertaining to this eclipse.
Eclipse season.
This eclipse is part of an eclipse season, a period, roughly every six months, when eclipses occur. Only two (or occasionally three) eclipse seasons occur each year, and each season lasts about 35 days and repeats just short of six months (173 days) later; thus two full eclipse seasons always occur each year. Either two or three eclipses happen each eclipse season. In the sequence below, each eclipse is separated by a fortnight.
Related eclipses.
Lunar eclipses of 1966–1969.
This eclipse is a member of a semester series. An eclipse in a semester series of lunar eclipses repeats approximately every 177 days and 4 hours (a semester) at alternating nodes of the Moon's orbit.
The penumbral lunar eclipse on August 27, 1969 occurs in the next lunar year eclipse set.
Saros 131.
This eclipse is a part of Saros series 131, repeating every 18 years, 11 days, and containing 72 events. The series started with a penumbral lunar eclipse on May 10, 1427. It contains partial eclipses from July 25, 1553 through March 22, 1932; total eclipses from April 2, 1950 through September 3, 2202; and a second set of partial eclipses from September 13, 2220 through April 9, 2563. The series ends at member 72 as a penumbral eclipse on July 7, 2707.
The longest duration of totality will be produced by member 38 at 100 minutes, 36 seconds on June 28, 2094. All eclipses in this series occur at the Moon’s descending node of orbit.
Eclipses are tabulated in three columns; every third eclipse in the same column is one exeligmos apart, so they all cast shadows over approximately the same parts of the Earth. 
Tritos series.
This eclipse is a part of a tritos cycle, repeating at alternating nodes every 135 synodic months (≈ 3986.63 days, or 11 years minus 1 month). Their appearance and longitude are irregular due to a lack of synchronization with the anomalistic month (period of perigee), but groupings of 3 tritos cycles (≈ 33 years minus 3 months) come close (≈ 434.044 anomalistic months), so eclipses are similar in these groupings.
Inex series.
The inex series repeats eclipses 20 days short of 29 years, repeating on average every 10571.95 days. This period is equal to 358 lunations (synodic months) and 388.5 draconic months. Saros series increment by one on successive Inex events and repeat at alternate ascending and descending lunar nodes.
This period is 383.6734 anomalistic months (the period of the Moon's elliptical orbital precession). Despite the average 0.05 time-of-day shift between subsequent events, the variation of the Moon in its elliptical orbit at each event causes the actual eclipse time to vary significantly. It is a part of Lunar Inex series 35.
Half-Saros cycle.
A lunar eclipse will be preceded and followed by solar eclipses by 9 years and 5.5 days (a half saros). This lunar eclipse is related to two annular solar eclipses of Solar Saros 138.
Notes.
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