Annular Solar eclipse September 7, 1820
An annular solar eclipse occurred at the Moon's descending node of orbit on Thursday, September 7, 1820, with a magnitude of 0.9329. 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 about 5 hours before apogee (on September 7, 1820, at 18:50 UTC), the Moon's apparent diameter was smaller.
The path of annularity was visible from parts of modern-day northern Canada, Greenland, western Norway, Denmark, the Netherlands, Germany, Switzerland, the Czech Republic, Austria, Italy, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, northeastern Libya, Egypt, Israel, Jordan, and Saudi Arabia. A partial solar eclipse was also visible for parts of northern North America, Europe, North Africa, the Middle East, and Central Asia.
Observation and prediction.
This map was drawn in the book "Elementa eclipsium", published in Prague in 1816, by Franz Ignaz Cassian Hallaschka (František Ignác Kassián Halaška) (1780-1847), contained maps of the paths of solar eclipses from 1816 and 1860. The geometric constructions used by Hallaschka anticipated the standard theory of eclipses later developed by Friedrich Wilhelm Bessel.
Eclipse details.
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.
Eclipse season.
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.
Related eclipses.
Solar eclipses of 1819–1823.
This eclipse is a member of a semester series. An eclipse in a semester series of solar eclipses repeats approximately every 177 days and 4 hours (a semester) at alternating nodes of the Moon's orbit.
The partial solar eclipses on April 24, 1819 and October 19, 1819 occur in the previous lunar year eclipse set, and the partial solar eclipses on January 12, 1823 and July 8, 1823 occur in the next lunar year eclipse set.
Saros 122.
This eclipse is a part of Saros series 122, repeating every 18 years, 11 days, and containing 70 events. The series started with a partial solar eclipse on April 17, 991 AD. It contains total eclipses from July 12, 1135 through August 3, 1171; hybrid eclipses on August 13, 1189 and August 25, 1207; and annular eclipses from September 4, 1225 through October 10, 1874. The series ends at member 70 as a partial eclipse on May 17, 2235. Its eclipses are tabulated in three columns; every third eclipse in the same column is one exeligmos apart, so they all cast shadows over approximately the same parts of the Earth. 
The longest duration of totality was produced by member 9 at 1 minutes, 25 seconds on July 12, 1135, and the longest duration of annularity was produced by member 50 at 6 minutes, 28 seconds on October 10, 1874. All eclipses in this series occur at the Moon’s descending node of orbit.
Metonic series.
The metonic series repeats eclipses every 19 years (6939.69 days), lasting about 5 cycles. Eclipses occur in nearly the same calendar date. In addition, the octon subseries repeats 1/5 of that or every 3.8 years (1387.94 days). All eclipses in this table occur at the Moon's descending node.
Tritos series.
This eclipse is a part of a tritos cycle, repeating at alternating nodes every 135 synodic months (≈ 3986.63 days, or 11 years minus 1 month). Their appearance and longitude are irregular due to a lack of synchronization with the anomalistic month (period of perigee), but groupings of 3 tritos cycles (≈ 33 years minus 3 months) come close (≈ 434.044 anomalistic months), so eclipses are similar in these groupings.
Inex series.
This eclipse is a part of the long period inex cycle, repeating at alternating nodes, every 358 synodic months (≈ 10,571.95 days, or 29 years minus 20 days). Their appearance and longitude are irregular due to a lack of synchronization with the anomalistic month (period of perigee). However, groupings of 3 inex cycles (≈ 87 years minus 2 months) comes close (≈ 1,151.02 anomalistic months), so eclipses are similar in these groupings.
Notes.
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