A total solar eclipse occurred at the Moon's descending node of orbit on Sunday, September 22, 1968,[1] with a magnitude of 1.0099. 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. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide. Occurring about 3.4 days before perigee (on September 25, 1968, at 21:20 UTC), the Moon's apparent diameter was larger.[2]
Totality was visible from the Soviet Union (today's Russia and Kazakhstan) and Xinjiang in Northwestern China. A partial eclipse was visible for parts of Europe, Northeast Africa, West Asia, Central Asia, and South Asia.
A company named Opton proposed to the Sternberg Astronomical Institute to observe this solar eclipse in Sary Shagan on the west bank of Lake Balkhash, and also wrote to the Soviet Ministry of Railways for help to get to the destination faster. The observation team obtained spectrum of the corona. Students also assisted in taking pictures of the corona with MTO-1000 lens.[3]
This is the first total solar eclipse visible in the country since the founding of the People's Republic of China. It occurred during the Cultural Revolution, when astronomers including Zhang Yuzhe who organized observations of the total solar eclipse of June 19, 1936 and September 21, 1941 were excluded from key positions. The Chinese Academy of Sciences sent a team of 200 including Zhang Kuisan (张魁三), the then deputy director of the Geophysics Bureau to Xinjiang. The observation was code-named "532", named after the time February 1953 when Mao Zedong visited the Purple Mountain Observatory in Nanjing. The travel to Ürümqi by train first took 3 days, and another 7 days by car to the optical observation site Zhaosu Town (Mongolküre Town), Zhaosu County and the radio observation site Kashgar. Gravity measurements were also conducted in mountain caves. In order to avoid the turmoil of the Cultural Revolution, Zhou Enlai sent Liu Xiyao to lead the army to the local area and provide the whole team with meals and accommodation. The observation team completed the first monochromatic light observation and high-resolution radio observation of the sun in China. This was also the first time in China that a solar eclipse was observed by plane. Shanghai Scientific and Educational Film Studio also produced a science and education film of the total solar eclipse.[4] [5]
The Soviet Union and China were the only two countries the path of this total solar eclipse passed. Due to the Sino-Soviet split, the two countries did not conduct any joint observations. About half a year after the eclipse, on January 23, 1969, the People's Daily published an article claiming that the observation of this eclipse "achieved brilliant results", repeatedly criticized the Soviet Union of "obstructing" it, and also mentioned that the Soviet Union "plundered data" of the annular solar eclipse of April 19, 1958.[6] [7]
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.[8]
| First Penumbral External Contact | 1968 September 22 at 09:07:22.9 UTC | |
| Equatorial Conjunction | 1968 September 22 at 10:22:09.4 UTC | |
| First Umbral External Contact | 1968 September 22 at 10:44:14.2 UTC | |
| First Central Line | 1968 September 22 at 10:44:37.1 UTC | |
| First Umbral Internal Contact | 1968 September 22 at 10:45:00.3 UTC | |
| Ecliptic Conjunction | 1968 September 22 at 11:08:44.2 UTC | |
| Greatest Eclipse | 1968 September 22 at 11:18:46.0 UTC | |
| Greatest Duration | 1968 September 22 at 11:20:13.7 UTC | |
| Last Umbral Internal Contact | 1968 September 22 at 11:53:04.0 UTC | |
| Last Central Line | 1968 September 22 at 11:53:29.7 UTC | |
| Last Umbral External Contact | 1968 September 22 at 11:53:55.1 UTC | |
| Last Penumbral External Contact | 1968 September 22 at 13:30:26.7 UTC |
| Eclipse Magnitude | 1.00990 | |
| Eclipse Obscuration | 1.01989 | |
| Gamma | 0.94507 | |
| Sun Right Ascension | 11h58m11.0s | |
| Sun Declination | +00°11'49.6" | |
| Sun Semi-Diameter | 15'56.3" | |
| Sun Equatorial Horizontal Parallax | 08.8" | |
| Moon Right Ascension | 11h59m58.7s | |
| Moon Declination | +01°00'16.0" | |
| Moon Semi-Diameter | 16'01.1" | |
| Moon Equatorial Horizontal Parallax | 0°58'47.3" | |
| ΔT | 38.9 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.