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Solar eclipse of April 18, 1977
An annular solar eclipse occurred at the Moon's descending node of orbit on Monday, April 18, 1977,[1] with a magnitude of 0.9449. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. An annular solar eclipse occurs when the Moon's apparent diameter is smaller than the Sun's, blocking most of the Sun's light and causing the Sun to look like an annulus (ring). An annular eclipse appears as a partial eclipse over a region of the Earth thousands of kilometres wide. Occurring about 3.1 days before apogee (on April 21, 1977, at 13:00 UTC), the Moon's apparent diameter was smaller.[2] Annularity was visible in South West Africa (today's Namibia), Angola, Zambia, southeastern Zaire (today's Democratic Republic of Congo), northern Malawi, Tanzania, Seychelles and the whole British Indian Ocean Territory. A partial eclipse was visible for parts of eastern Brazil, Southern Africa, Central Africa, East Africa, Antarctica, the Middle East, and South Asia. Eclipse detailsShown below are two tables displaying details about this particular solar eclipse. The first table outlines times at which the moon's penumbra or umbra attains the specific parameter, and the second table describes various other parameters pertaining to this eclipse.[3]
Eclipse seasonThis 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 eclipsesEclipses in 1977
Metonic
Tzolkinex
Half-Saros
Tritos
Solar Saros 138
Inex
Triad
Solar eclipses of 1975–1978This eclipse is a member of a semester series. An eclipse in a semester series of solar eclipses repeats approximately every 177 days and 4 hours (a semester) at alternating nodes of the Moon's orbit.[4]
Saros 138This eclipse is a part of Saros series 138, repeating every 18 years, 11 days, and containing 70 events. The series started with a partial solar eclipse on June 6, 1472. It contains annular eclipses from August 31, 1598 through February 18, 2482; a hybrid eclipse on March 1, 2500; and total eclipses from March 12, 2518 through April 3, 2554. The series ends at member 70 as a partial eclipse on July 11, 2716. Its 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. The longest duration of annularity was produced by member 23 at 8 minutes, 2 seconds on February 11, 1869, and the longest duration of totality will be produced by member 61 at 56 seconds on April 3, 2554. All eclipses in this series occur at the Moon’s descending node of orbit.[5]
Metonic seriesThe metonic series repeats eclipses every 19 years (6939.69 days), lasting about 5 cycles. Eclipses occur in nearly the same calendar date. In addition, the octon subseries repeats 1/5 of that or every 3.8 years (1387.94 days). All eclipses in this table occur at the Moon's descending node.
Tritos seriesThis 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 seriesThis eclipse is a part of the long period inex cycle, repeating at alternating nodes, every 358 synodic months (≈ 10,571.95 days, or 29 years minus 20 days). Their appearance and longitude are irregular due to a lack of synchronization with the anomalistic month (period of perigee). However, groupings of 3 inex cycles (≈ 87 years minus 2 months) comes close (≈ 1,151.02 anomalistic months), so eclipses are similar in these groupings.
Notes
References
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