An annular solar eclipse occurred at the Moon's ascending node of orbit between Saturday, May 8 and Sunday, May 9, 1948,[1] with a magnitude of 0.9999. 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 7 days after apogee (on May 2, 1948, at 2:00 UTC) and 6.7 days before perigee (on May 15, 1948, at 17:10 UTC).[2]
The moon's apparent diameter was only 0.006% smaller than the Sun's, so this was an annular solar eclipse that occurred on May 9. The path width of this large annular solar eclipse, was about 200 meters and lasted only 0.3 seconds. The large annular eclipse covered over 99% of the Sun, creating a dramatic spectacle for observers in only an extremely narrow strip; however, it was fleeting, lasting just moments at the point of maximum eclipse.
Annularity was visible from Car Nicobar, the northernmost of the Nicobar Islands, and Burma, Siam (now renamed to Thailand) including Bangkok, French Indochina (the part now belonging to Laos), North Vietnam (now belonging to Vietnam), China, South Korea, Rebun Island in Japan, Kuril Islands in the Soviet Union (now belonging to Russia) on May 9, and Alaska on May 8. A partial eclipse was visible for parts of South Asia, Southeast Asia, East Asia, Northeast Asia, Alaska, and northwest Canada.
This was the first 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.
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. The National Geographic Society sent 7 teams respectively to Myeik in Burma, Bangkok in Siam, Wukang County (now belonging to Deqing County, Zhejiang) in China, of (now Onyang-dong, Asan City) in South Korea, Rebun Island in Japan, Adak Island in Alaska, as well as from the air onboard a Boeing B-29 Superfortress departing from Shemya Island. The scale of this observation was larger than ever before. In the end, the teams from the air and on Rebun Island got the best results with good weather conditions, while the results in Myeik and Bangkok were relatively good, Adak Island still somewhat valuable, Onyang-eup missing many goals, and Wukang with the worst results where there was rain during the eclipse. It was shortly after the end of World War II, and the observation in Japan showed friendship among the science community.[3], one of the two villages on the island, supported the observation team, and a Solar Eclipse Observation Monument was built in 1954 to commemorate it.[4] [5] The monument was first erected in Kitousu, the center of the observation site. It was moved to Itsukushima Shrine in 2003, across the sea facing Rishirifuji.[6]
Prior to it, the two hybrid solar eclipses of April 17, 1912 and April 28, 1930, also belonging to Solar Saros 137, also occurred with a magnitude close to 1. Observations were made near Paris, France and Camptonville, California respectively. There was an opportunity to make similar observations during the annular solar eclipse of May 20, 1966 in Greece and Turkey, also belonging to the same solar Saros cycle.[4]
The Institute of Astronomy of the Academia Sinica (predecessor of Purple Mountain Observatory), Department of Physics of National Central University and Bureau of Surveying of the Ministry of National Defense also formed a team. The initial plan was to go to Guangdong, far from the observation site of the American team, hoping that the two teams would not be affected by bad weather at the same time. However after checking the weather, traffic and law and order conditions near Guangzhou, Hangzhou and Suzhou, the team finally decided on Cibiwu in Yuhang County. The decision was made based on the fact that meteorological data showed bad conditions generally across the whole Jiangnan in May, within the East Asian rainy season, and funding is limited so travel could not be made for a long distance. Besides, Xujiahui (Zi-Ka-Wei) Observatory estimated that there was 70% hope in Cibiwu, and it is close to the observation site of the American team, allowing the Chinese team to see the equipment of the American team for future reference.[7] Zhang Yuzhe, director of the Institute of Astronomy, visited the United States and Canada to study the spectrum of eclipsing binaries in 1946. However, the Ministry of Foreign Affairs of the Republic of China stopped funding him the return trip back to China. He took the opportunity of joining the observation team to return to China in March 1948,[8] and observed it together with .[9] In the end, due to the weather conditions, just like the American team which traveled to China, the Chinese team also only measured changes in the luminosity of the sun. The Qingdao Observatory, Sun Yat-sen University Observatory and the Department of Physics of Tongji University also made observations.[10]
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.[11]
| First Penumbral External Contact | 1948 May 08 at 23:40:23.2 UTC | |
| First Umbral External Contact | 1948 May 09 at 00:44:35.7 UTC | |
| First Central Line | 1948 May 09 at 00:45:07.7 UTC | |
| Greatest Duration | 1948 May 09 at 00:45:07.7 UTC | |
| First Umbral Internal Contact | 1948 May 09 at 00:45:39.6 UTC | |
| First Penumbral Internal Contact | 1948 May 09 at 02:06:53.9 UTC | |
| Greatest Eclipse | 1948 May 09 at 02:26:03.6 UTC | |
| Ecliptic Conjunction | 1948 May 09 at 02:30:35.8 UTC | |
| Equatorial Conjunction | 1948 May 09 at 02:44:18.7 UTC | |
| Last Penumbral Internal Contact | 1948 May 09 at 02:44:48.6 UTC | |
| Last Umbral Internal Contact | 1948 May 09 at 04:06:18.3 UTC | |
| Last Central Line | 1948 May 09 at 04:06:47.3 UTC | |
| Last Umbral External Contact | 1948 May 09 at 04:07:16.3 UTC | |
| Last Penumbral External Contact | 1948 May 09 at 05:11:30.1 UTC |
| Eclipse Magnitude | 0.99994 | |
| Eclipse Obscuration | 0.99989 | |
| Gamma | 0.41332 | |
| Sun Right Ascension | 03h03m37.8s | |
| Sun Declination | +17°18'09.3" | |
| Sun Semi-Diameter | 15'50.3" | |
| Sun Equatorial Horizontal Parallax | 08.7" | |
| Moon Right Ascension | 03h03m01.1s | |
| Moon Declination | +17°40'05.5" | |
| Moon Semi-Diameter | 15'36.6" | |
| Moon Equatorial Horizontal Parallax | 0°57'17.4" | |
| ΔT | 28.4 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.