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Solar eclipse of April 18, 1977

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Solar eclipse of April 18, 1977
Map
Type of eclipse
NatureAnnular
Gamma−0.399
Magnitude0.9449
Maximum eclipse
Duration424 s (7 min 4 s)
Coordinates11°54′S 28°18′E / 11.9°S 28.3°E / -11.9; 28.3
Max. width of band220 km (140 mi)
Times (UTC)
Greatest eclipse10:31:30
References
Saros138 (29 of 70)
Catalog # (SE5000)9458

An annular solar eclipse occurred at the Moon's descending node of orbit on Monday, April 18, 1977,[1] with a magnitude of 0.9449. 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 about 3.1 days before apogee (on April 21, 1977, at 13:00 UTC), the Moon's apparent diameter was smaller.[2]

Annularity was visible in South West Africa (today's Namibia), Angola, Zambia, southeastern Zaire (today's Democratic Republic of Congo), northern Malawi, Tanzania, Seychelles and the whole British Indian Ocean Territory. A partial eclipse was visible for parts of eastern Brazil, Southern Africa, Central Africa, East Africa, Antarctica, the Middle East, and South Asia.

Eclipse details

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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.[3]

April 18, 1977 Solar Eclipse Times
Event Time (UTC)
First Penumbral External Contact 1977 April 18 at 07:33:32.8 UTC
First Umbral External Contact 1977 April 18 at 08:41:17.9 UTC
First Central Line 1977 April 18 at 08:43:51.9 UTC
First Umbral Internal Contact 1977 April 18 at 08:46:26.6 UTC
First Penumbral Internal Contact 1977 April 18 at 10:12:31.9 UTC
Equatorial Conjunction 1977 April 18 at 10:18:48.0 UTC
Greatest Eclipse 1977 April 18 at 10:31:29.9 UTC
Ecliptic Conjunction 1977 April 18 at 10:36:13.6 UTC
Greatest Duration 1977 April 18 at 10:40:30.0 UTC
Last Penumbral Internal Contact 1977 April 18 at 10:50:48.6 UTC
Last Umbral Internal Contact 1977 April 18 at 12:16:41.3 UTC
Last Central Line 1977 April 18 at 12:19:17.4 UTC
Last Umbral External Contact 1977 April 18 at 12:21:52.9 UTC
Last Penumbral External Contact 1977 April 18 at 13:29:36.4 UTC
April 18, 1977 Solar Eclipse Parameters
Parameter Value
Eclipse Magnitude 0.94492
Eclipse Obscuration 0.89288
Gamma −0.39903
Sun Right Ascension 01h45m03.2s
Sun Declination +10°51'37.2"
Sun Semi-Diameter 15'55.5"
Sun Equatorial Horizontal Parallax 08.8"
Moon Right Ascension 01h45m26.3s
Moon Declination +10°30'41.9"
Moon Semi-Diameter 14'50.4"
Moon Equatorial Horizontal Parallax 0°54'28.0"
ΔT 47.8 s

Eclipse season

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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.

Eclipse season of April 1977
April 4
Ascending node (full moon)
April 18
Descending node (new moon)
Partial lunar eclipse
Lunar Saros 112
Annular solar eclipse
Solar Saros 138
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Eclipses in 1977

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Metonic

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Tzolkinex

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Half-Saros

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Tritos

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Solar Saros 138

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Inex

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Triad

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Solar eclipses of 1975–1978

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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.[4]

Solar eclipse series sets from 1975 to 1978
Descending node   Ascending node
Saros Map Gamma Saros Map Gamma
118 May 11, 1975

Partial
1.0647 123 November 3, 1975

Partial
−1.0248
128 April 29, 1976

Annular
0.3378 133 October 23, 1976

Total
−0.327
138 April 18, 1977

Annular
−0.399 143 October 12, 1977

Total
0.3836
148 April 7, 1978

Partial
−1.1081 153 October 2, 1978

Partial
1.1616

Saros 138

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This eclipse is a part of Saros series 138, repeating every 18 years, 11 days, and containing 70 events. The series started with a partial solar eclipse on June 6, 1472. It contains annular eclipses from August 31, 1598 through February 18, 2482; a hybrid eclipse on March 1, 2500; and total eclipses from March 12, 2518 through April 3, 2554. The series ends at member 70 as a partial eclipse on July 11, 2716. 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 annularity was produced by member 23 at 8 minutes, 2 seconds on February 11, 1869, and the longest duration of totality will be produced by member 61 at 56 seconds on April 3, 2554. All eclipses in this series occur at the Moon’s descending node of orbit.[5]

Series members 20–41 occur between 1801 and 2200:
20 21 22

January 10, 1815

January 20, 1833

February 1, 1851
23 24 25

February 11, 1869

February 22, 1887

March 6, 1905
26 27 28

March 17, 1923

March 27, 1941

April 8, 1959
29 30 31

April 18, 1977

April 29, 1995

May 10, 2013
32 33 34

May 21, 2031

May 31, 2049

June 11, 2067
35 36 37

June 22, 2085

July 4, 2103

July 14, 2121
38 39 40

July 25, 2139

August 5, 2157

August 16, 2175
41

August 26, 2193

Metonic series

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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.

22 eclipse events between September 12, 1931 and July 1, 2011
September 11–12 June 30–July 1 April 17–19 February 4–5 November 22–23
114 116 118 120 122

September 12, 1931

June 30, 1935

April 19, 1939

February 4, 1943

November 23, 1946
124 126 128 130 132

September 12, 1950

June 30, 1954

April 19, 1958

February 5, 1962

November 23, 1965
134 136 138 140 142

September 11, 1969

June 30, 1973

April 18, 1977

February 4, 1981

November 22, 1984
144 146 148 150 152

September 11, 1988

June 30, 1992

April 17, 1996

February 5, 2000

November 23, 2003
154 156

September 11, 2007

July 1, 2011

Tritos series

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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.

Series members between 1801 and 2200

August 28, 1802
(Saros 122)

July 27, 1813
(Saros 123)

June 26, 1824
(Saros 124)

May 27, 1835
(Saros 125)

April 25, 1846
(Saros 126)

March 25, 1857
(Saros 127)

February 23, 1868
(Saros 128)

January 22, 1879
(Saros 129)

December 22, 1889
(Saros 130)

November 22, 1900
(Saros 131)

October 22, 1911
(Saros 132)

September 21, 1922
(Saros 133)

August 21, 1933
(Saros 134)

July 20, 1944
(Saros 135)

June 20, 1955
(Saros 136)

May 20, 1966
(Saros 137)

April 18, 1977
(Saros 138)

March 18, 1988
(Saros 139)

February 16, 1999
(Saros 140)

January 15, 2010
(Saros 141)

December 14, 2020
(Saros 142)

November 14, 2031
(Saros 143)

October 14, 2042
(Saros 144)

September 12, 2053
(Saros 145)

August 12, 2064
(Saros 146)

July 13, 2075
(Saros 147)

June 11, 2086
(Saros 148)

May 11, 2097
(Saros 149)

April 11, 2108
(Saros 150)

March 11, 2119
(Saros 151)

February 8, 2130
(Saros 152)

January 8, 2141
(Saros 153)

December 8, 2151
(Saros 154)

November 7, 2162
(Saros 155)

October 7, 2173
(Saros 156)

September 4, 2184
(Saros 157)

August 5, 2195
(Saros 158)

Inex series

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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.

Series members between 1801 and 2200

August 17, 1803
(Saros 132)

July 27, 1832
(Saros 133)

July 8, 1861
(Saros 134)

June 17, 1890
(Saros 135)

May 29, 1919
(Saros 136)

May 9, 1948
(Saros 137)

April 18, 1977
(Saros 138)

March 29, 2006
(Saros 139)

March 9, 2035
(Saros 140)

February 17, 2064
(Saros 141)

January 27, 2093
(Saros 142)

January 8, 2122
(Saros 143)

December 19, 2150
(Saros 144)

November 28, 2179
(Saros 145)

Notes

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  1. ^ "April 18, 1977 Annular Solar Eclipse". timeanddate. Retrieved 8 August 2024.
  2. ^ "Moon Distances for London, United Kingdom, England". timeanddate. Retrieved 8 August 2024.
  3. ^ "Annular Solar Eclipse of 1977 Apr 18". EclipseWise.com. Retrieved 8 August 2024.
  4. ^ van Gent, R.H. "Solar- and Lunar-Eclipse Predictions from Antiquity to the Present". A Catalogue of Eclipse Cycles. Utrecht University. Retrieved 6 October 2018.
  5. ^ "NASA - Catalog of Solar Eclipses of Saros 138". eclipse.gsfc.nasa.gov.

References

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