An annular solar eclipse occurred at the Moon's descending node of orbit on Wednesday, September 23, 1987,[1] with a magnitude of 0.9634. 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 only 5 days after apogee (on September 18, 1987, at 4:00 UTC), the Moon's apparent diameter was smaller.[2]
Annularity was visible in the Soviet Union (today's Kazakhstan), China (including Shanghai), southwestern Mongolia, Okinawa Islands of Japan except Kume Island and the southwestern tip of Kerama Islands, the Federal States of Micronesia, Papua New Guinea, Solomon Islands, Rotuma Islands of Fiji, Wallis Islands and West Samoa (the name changed to Samoa later). A partial eclipse was visible for parts of South Asia, Southeast Asia, East Asia, Australia, Oceania, and Hawaii.
Five radio observation stations were present in China at the time of the eclipse, two of which were within the annularity, in Ürümqi and Shanghai respectively. A partial solar eclipse was observed from the other three, including one in Nanjing where the eclipse was close to annularity, and the rest two in Beijing and Kunming. The Department of Mathematics and Physics of the Chinese Academy of Sciences and the Chinese Astronomical Society held a meeting in Kunming in December 1986, deciding that on-site observation would be conducted at each station, among which the Shanghai Astronomical Observatory was considered to have the best location with a larger magnitude of the eclipse, longer duration and larger solar zenith angle. The Shanghai Astronomical Observatory conducted observations with seven different wave bands using a 25-metre radio telescope.[3] The Yunnan Astronomical Observatory located in Kunming also conducted a multi-band joint observation of the partial solar eclipse.[4]
The Chinese Research Institute of Radio Wave Propagation conducted observations with a high-frequency skywave radar located in Xinxiang on the southern limit of annularity. Uneven structure and motion were observed in the ionosphere, the highest operating frequency was found changed during the eclipse, and large-scale fluctuations continued after the eclipse.[5]
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.[6]
| First Penumbral External Contact | 1987 September 23 at 00:15:50.5 UTC | |
| First Umbral External Contact | 1987 September 23 at 01:20:19.5 UTC | |
| First Central Line | 1987 September 23 at 01:22:07.2 UTC | |
| First Umbral Internal Contact | 1987 September 23 at 01:23:55.0 UTC | |
| First Penumbral Internal Contact | 1987 September 23 at 02:33:48.6 UTC | |
| Greatest Duration | 1987 September 23 at 02:45:44.7 UTC | |
| Equatorial Conjunction | 1987 September 23 at 02:54:28.0 UTC | |
| Ecliptic Conjunction | 1987 September 23 at 03:09:08.4 UTC | |
| Greatest Eclipse | 1987 September 23 at 03:12:21.6 UTC | |
| Last Penumbral Internal Contact | 1987 September 23 at 03:51:20.8 UTC | |
| Last Umbral Internal Contact | 1987 September 23 at 05:01:01.1 UTC | |
| Last Central Line | 1987 September 23 at 05:02:46.3 UTC | |
| Last Umbral External Contact | 1987 September 23 at 05:04:31.2 UTC | |
| Last Penumbral External Contact | 1987 September 23 at 06:08:54.0 UTC |
| Eclipse Magnitude | 0.96337 | |
| Eclipse Obscuration | 0.92807 | |
| Gamma | 0.27869 | |
| Sun Right Ascension | 11h58m25.1s | |
| Sun Declination | +00°10'17.1" | |
| Sun Semi-Diameter | 15'56.2" | |
| Sun Equatorial Horizontal Parallax | 08.8" | |
| Moon Right Ascension | 11h58m55.2s | |
| Moon Declination | +00°23'45.5" | |
| Moon Semi-Diameter | 15'07.6" | |
| Moon Equatorial Horizontal Parallax | 0°55'30.9" | |
| ΔT | 55.7 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.