An annular solar eclipse occurred at the Moon's ascending node of orbit on Monday, December 24, 1973,[1] with a magnitude of 0.9174. 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 1.25 days before apogee (on December 25, 1973, at 21:30 UTC), the Moon's apparent diameter was smaller.[2]
The duration of annularity at maximum eclipse (closest to but slightly shorter than the longest duration) was 12 minutes, 2.37 seconds in the Atlantic Ocean near the Brazilian coast. It was the longest annular solar eclipse until January 14, 3080, but the Solar eclipse of December 14, 1955 lasted longer.[3]
Annularity was visible from southern Mexico, southwestern Nicaragua, Costa Rica including the capital city San José, Panama, Colombia including the capital city Bogotá, southern Venezuela, Brazil, southern Guyana, southern Dutch Guiana (today's Suriname), southern French Guiana, Portuguese Cape Verde (today's Cape Verde) including the capital city Praia, Mauritania including the capital city Nouakchott, Spanish Sahara (today's Western Sahara), Mali, and Algeria. A partial eclipse was visible for parts of eastern North America, Central America, the Caribbean, northern and central South America, Western Europe, and West Africa.
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.[4]
| First Penumbral External Contact | 1973 December 24 at 12:01:48.2 UTC | |
| First Umbral External Contact | 1973 December 24 at 13:10:43.7 UTC | |
| First Central Line | 1973 December 24 at 13:14:29.7 UTC | |
| First Umbral Internal Contact | 1973 December 24 at 13:18:17.1 UTC | |
| First Penumbral Internal Contact | 1973 December 24 at 14:54:55.3 UTC | |
| Greatest Duration | 1973 December 24 at 14:57:39.1 UTC | |
| Greatest Eclipse | 1973 December 24 at 15:02:43.5 UTC | |
| Ecliptic Conjunction | 1973 December 24 at 15:07:45.5 UTC | |
| Equatorial Conjunction | 1973 December 24 at 15:08:46.6 UTC | |
| Last Penumbral Internal Contact | 1973 December 24 at 15:10:21.8 UTC | |
| Last Umbral Internal Contact | 1973 December 24 at 16:47:05.3 UTC | |
| Last Central Line | 1973 December 24 at 16:50:53.5 UTC | |
| Last Umbral External Contact | 1973 December 24 at 16:54:40.4 UTC | |
| Last Penumbral External Contact | 1973 December 24 at 18:03:38.0 UTC |
| Eclipse Magnitude | 0.91745 | |
| Eclipse Obscuration | 0.84171 | |
| Gamma | 0.41710 | |
| Sun Right Ascension | 18h11m38.6s | |
| Sun Declination | -23°24'56.0" | |
| Sun Semi-Diameter | 16'15.7" | |
| Sun Equatorial Horizontal Parallax | 08.9" | |
| Moon Right Ascension | 18h11m26.8s | |
| Moon Declination | -23°02'37.9" | |
| Moon Semi-Diameter | 14'43.0" | |
| Moon Equatorial Horizontal Parallax | 0°54'00.7" | |
| ΔT | 44.5 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.