An annular solar eclipse occurred at the Moon's ascending node of orbit on Friday, May 20, 1966,[1] with a magnitude of 0.9991. 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. The Moon's apparent diameter was near the average diameter because it occurred 6.8 days after apogee (on May 13, 1966, at 14:00 UTC) and 7.2 days before perigee (on May 27, 1966, at 15:00 UTC).[2]
Annularity was visible from Guinea (including the capital city Conakry), Mali, Algeria, Libya, Greece, Turkey, the Soviet Union (today's Russia and Kazakhstan) and China. A partial eclipse was visible for parts of North Africa, Central Africa, Northeast Africa, Europe, West Asia, Central Asia, North Asia, and South Asia.
During this eclipse, the apex of the moon's umbral cone was very close to the Earth's surface, and the magnitude was very large. The edges of the moon and the sun were very close to each other as seen from the Earth. Baily's beads on the lunar limb, which are usually only visible during a total solar eclipse, could also be seen. Therefore this eclipse was also an excellent opportunity to measure the size and shape of the Earth, as well as the mountains and valleys on the lunar limb. Many scientists observed the annular eclipse in Greece and Turkey, which are close to the location of maximum eclipse and have better observation conditions. The observation sites in Greece were mainly concentrated in Saronida and Anavyssos south of Athens, while those in Turkey were mainly concentrated in Ayvalik, across the sea facing the Greek island Lesbos.[3]
Similar to the Baily's beads, the corona is generally only visible in a total solar eclipse. Because the magnitude of this annular eclipse was close to 1, some predicted that the corona would be visible. An observation team went to Lesbos Island but only saw the Baily's beads, not the corona.[4]
Prior to it, the two hybrid solar eclipses of April 17, 1912 and April 28, 1930, and another annular solar eclipse of May 9, 1948 also belonging to Solar Saros 137, also occurred with a magnitude close to 1. Observations were made near Paris in France, Camptonville, California and Rebun Island in Japan respectively.[3]
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.[5]
| First Penumbral External Contact | 1966 May 20 at 06:50:51.2 UTC | |
| First Umbral External Contact | 1966 May 20 at 07:54:07.8 UTC | |
| First Central Line | 1966 May 20 at 07:54:41.4 UTC | |
| Greatest Duration | 1966 May 20 at 07:54:41.4 UTC | |
| First Umbral Internal Contact | 1966 May 20 at 07:55:14.9 UTC | |
| First Penumbral Internal Contact | 1966 May 20 at 09:07:24.3 UTC | |
| Greatest Eclipse | 1966 May 20 at 09:39:01.6 UTC | |
| Ecliptic Conjunction | 1966 May 20 at 09:42:51.0 UTC | |
| Equatorial Conjunction | 1966 May 20 at 09:51:45.8 UTC | |
| Last Penumbral Internal Contact | 1966 May 20 at 10:10:21.8 UTC | |
| Last Umbral Internal Contact | 1966 May 20 at 11:22:42.3 UTC | |
| Last Central Line | 1966 May 20 at 11:23:12.9 UTC | |
| Last Umbral External Contact | 1966 May 20 at 11:23:43.5 UTC | |
| Last Penumbral External Contact | 1966 May 20 at 12:27:00.2 UTC |
| Eclipse Magnitude | 0.99915 | |
| Eclipse Obscuration | 0.99830 | |
| Gamma | 0.34672 | |
| Sun Right Ascension | 03h46m47.1s | |
| Sun Declination | +19°55'23.3" | |
| Sun Semi-Diameter | 15'48.2" | |
| Sun Equatorial Horizontal Parallax | 08.7" | |
| Moon Right Ascension | 03h46m20.7s | |
| Moon Declination | +20°14'08.1" | |
| Moon Semi-Diameter | 15'33.4" | |
| Moon Equatorial Horizontal Parallax | 0°57'05.7" | |
| ΔT | 36.9 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.