An annular solar eclipse occurred at the Moon's descending node of orbit on Saturday, April 19, 1958,[1] with a magnitude of 0.9408. 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 2.2 days after apogee (on April 16, 1958, at 22:40 UTC), the Moon's apparent diameter was smaller.[2]
Annularity was visible in the Maldives, Nicobar Islands, Burma, Thailand including the capital city Bangkok, Cambodia, Laos, North Vietnam and South Vietnam (now belonging to Vietnam), China, British Hong Kong, Taiwan, Ryukyu Islands and Japan. Places east of International Date line witnessed the eclipse on April 18 (Friday). A partial eclipse was visible for most of Asia.
This was the last of four central solar eclipses visible from Bangkok from 1948 to 1958, where it is extremely rare for a large city to witness four central solar eclipses within 10 years.
Compared with a total solar eclipse, the chromosphere, corona and solar prominence are invisible during an annular eclipse. However, observations of millimeter-wave solar radio can provide data for lower- and mid-layer structure of the chromosphere, which is more valuable during an annular solar eclipse.[3]
A joint observation team formed by the Academy of Sciences of the Soviet Union (predecessor of today's Russian Academy of Sciences) and the Chinese Academy of Sciences conducted 8-millimeter radio observation in Sanya, Hainan Island, China using the equatorial parabolic radio telescope manufactured by the Lebedev Physical Institute and the dual-channel radiometer as a receiver.[3] [4] Radio astronomy started to develop from then in China.[5] Due to the Sino-Soviet split soon after this eclipse, the two countries did not conduct any joint observations of the total solar eclipse of September 22, 1968. On January 23, 1969, the People's Daily published an article reporting the observation of the eclipse in 1968, where it also criticized that the Soviet Union "plundered data of the annular solar eclipse" in 1958, only left China a "worn radio telescope antenna", and later even asked for it back.[6]
Observation ships were sent to Hachijō-jima, Izu Islands, Japan.[7] Pictures were also taken in Tanegashima, Osumi Islands, and luminosity, air pressure, temperature, humidity, water temperature of the storage tank, ground temperature, wind direction, wind speed and other data were recorded every 10 minutes.[8]
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.[9]
| First Penumbral External Contact | 1958 April 19 at 00:24:41.6 UTC | |
| First Umbral External Contact | 1958 April 19 at 01:30:53.9 UTC | |
| First Central Line | 1958 April 19 at 01:33:33.8 UTC | |
| First Umbral Internal Contact | 1958 April 19 at 01:36:14.1 UTC | |
| First Penumbral Internal Contact | 1958 April 19 at 02:47:56.9 UTC | |
| Ecliptic Conjunction | 1958 April 19 at 03:23:59.6 UTC | |
| Greatest Eclipse | 1958 April 19 at 03:27:16.7 UTC | |
| Greatest Duration | 1958 April 19 at 03:33:53.0 UTC | |
| Equatorial Conjunction | 1958 April 19 at 03:36:02.5 UTC | |
| Last Penumbral Internal Contact | 1958 April 19 at 04:06:22.2 UTC | |
| Last Umbral Internal Contact | 1958 April 19 at 05:18:13.8 UTC | |
| Last Central Line | 1958 April 19 at 05:20:52.8 UTC | |
| Last Umbral External Contact | 1958 April 19 at 05:23:31.5 UTC | |
| Last Penumbral External Contact | 1958 April 19 at 06:29:44.7 UTC |
| Eclipse Magnitude | 0.94082 | |
| Eclipse Obscuration | 0.88515 | |
| Gamma | 0.27499 | |
| Sun Right Ascension | 01h46m12.4s | |
| Sun Declination | +10°58'10.3" | |
| Sun Semi-Diameter | 15'55.4" | |
| Sun Equatorial Horizontal Parallax | 08.8" | |
| Moon Right Ascension | 01h45m56.6s | |
| Moon Declination | +11°12'31.2" | |
| Moon Semi-Diameter | 14'45.9" | |
| Moon Equatorial Horizontal Parallax | 0°54'11.2" | |
| ΔT | 32.3 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. The first and last eclipse in this sequence is separated by one synodic month.