Solar eclipse of May 9, 1948

An annular solar eclipse occurred at the Moon's ascending node of orbit on Sunday, May 9, 1948, 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. 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. It was the first central solar eclipse visible from Bangkok from 1948 to 1958, where it is rare for a large city to witness 4 central solar eclipses in 10 years. 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, 1948. Occurring 7.1 days after apogee (on May 2, 1948) and 6.6 days before perigee (Perigee on May 15, 1948), the Moon's apparent diameter was near the average diameter.

The path width of the large annular solar eclipse of May 9, 1948, was about 200 meters and lasted only 0.3 seconds. A 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.

Observations
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, Onyang City of Asan-gun (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. Kafuka, 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. 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.

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.

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. 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, and observed it together with Chen Zungui. 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.

Eclipses in 1948

 * A partial lunar eclipse on April 23, 1948.
 * An annular solar eclipse on May 9, 1948.
 * A penumbral lunar eclipse on October 18, 1948.
 * A total solar eclipse on November 1, 1948.

Metonic

 * Preceded by: Solar eclipse of July 20, 1944
 * Followed by: Solar eclipse of February 25, 1952

Tzolkinex

 * Preceded by: Solar eclipse of March 27, 1941
 * Followed by: Solar eclipse of June 20, 1955

Half-Saros

 * Preceded by: Lunar eclipse of May 3, 1939
 * Followed by: Lunar eclipse of May 13, 1957

Tritos

 * Preceded by: Solar eclipse of June 8, 1937
 * Followed by: Solar eclipse of April 8, 1959

Solar Saros 137

 * Preceded by: Solar eclipse of April 28, 1930
 * Followed by: Solar eclipse of May 20, 1966

Inex

 * Preceded by: Solar eclipse of May 29, 1919
 * Followed by: Solar eclipse of April 18, 1977

Triad

 * Preceded by: Solar eclipse of July 8, 1861
 * Followed by: Solar eclipse of March 9, 2035