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.
Shown 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]
| First Penumbral External Contact | 1977 April 18 at 07:33:32.8 UTC | |
| First Umbral External Contact | 1977 April 18 at 08:41:17.9 UTC | |
| First Central Line | 1977 April 18 at 08:43:51.9 UTC | |
| First Umbral Internal Contact | 1977 April 18 at 08:46:26.6 UTC | |
| First Penumbral Internal Contact | 1977 April 18 at 10:12:31.9 UTC | |
| Equatorial Conjunction | 1977 April 18 at 10:18:48.0 UTC | |
| Greatest Eclipse | 1977 April 18 at 10:31:29.9 UTC | |
| Ecliptic Conjunction | 1977 April 18 at 10:36:13.6 UTC | |
| Greatest Duration | 1977 April 18 at 10:40:30.0 UTC | |
| Last Penumbral Internal Contact | 1977 April 18 at 10:50:48.6 UTC | |
| Last Umbral Internal Contact | 1977 April 18 at 12:16:41.3 UTC | |
| Last Central Line | 1977 April 18 at 12:19:17.4 UTC | |
| Last Umbral External Contact | 1977 April 18 at 12:21:52.9 UTC | |
| Last Penumbral External Contact | 1977 April 18 at 13:29:36.4 UTC |
| Eclipse Magnitude | 0.94492 | |
| Eclipse Obscuration | 0.89288 | |
| Gamma | −0.39903 | |
| Sun Right Ascension | 01h45m03.2s | |
| Sun Declination | +10°51'37.2" | |
| Sun Semi-Diameter | 15'55.5" | |
| Sun Equatorial Horizontal Parallax | 08.8" | |
| Moon Right Ascension | 01h45m26.3s | |
| Moon Declination | +10°30'41.9" | |
| Moon Semi-Diameter | 14'50.4" | |
| Moon Equatorial Horizontal Parallax | 0°54'28.0" | |
| ΔT | 47.8 s |
See also: Eclipse cycle. 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.