Astronomy Answers
Planetary Phenomena 1991


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The diagram below is explained further on the page for the year 2000.

1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105

[1991] [Q 1991]

For an explanation of the above pictures, see the page for the year 2000.

The last table on this page lists a number of noteworthy planetary phenomena during the listed year. The first column ("date") gives the date and hour, in the form year-month-dayThour in the Gregorian calendar, in Universal Time (UT). The second column ("pl") identifies the planet that shows the phenomenon:

pl Planet
Me Mercury
Ve Venus
Ma Mars
Ju Jupiter
Sa Saturn
Ur Uranus
Ne Neptune
Lu Moon

The third column ("*") provides the type of the phenomenon. The fourth column ("AU") shows the value (distance) in Astronomical Units, if applicable. The fifth column ("deg") gives the value of a relevant angle (declination \( δ \), elongation \( E \), conjunction spread \( σ \), or ecliptic longitude \( λ \)) in degrees. Which angle it is for each phenomenon is shown below in column "?". Declinations and ecliptical longitudes are measured relative to the equinox of the date.

 ?  
Explanation
p perigee
a apogee
+dδgreatest northern declination
dδgreatest southern declination
cλconjunction (with the Sun)
oλopposition (relative to the Sun)
eEgreatest elongation
xaλpassage through the ascending node (zero ecliptical latitude)
xdλpassage through the descending node (zero ecliptical latitude)
bσleast conjunction spread (Mercury - Saturn)
Bσleast conjunction spread (Mercury - Neptune)
sσgreatest conjunction spread (Mercury - Saturn)
Sσgreatest conjunction spread (Mercury - Neptune)
Vλbegin eastward (prograde) acceleration
Pgλstationary point: begin eastward (prograde) motion
vλbegin westward (retrograde) acceleration
Rgλstationary point: begin westward (retrograde) motion

The calculations for the planets are based on the VSOP87 model (type A) of Laskar, and the calculations for the Moon are based on the most detailed model from [Meeus]. One position per day was calculated for each celestial object. The hour of the day for each phenomenon was determined by interpolation.

date pl * AU deg
1991−01−01T12 Ma Pg +57.75
1991−01−01T23 Lu xd +118.03
1991−01−03T17 Me Pg +263.70
1991−01−03T21
** 
s +184.96
1991−01−05T02 Ne a 31.19
1991−01−05T03 Ne c +284.28
1991−01−05T10 Ne v +284.29
1991−01−09T09 Pl d −3.22
1991−01−12T09 Lu V +252.39
1991−01−12T11 Lu a 0.002714
1991−01−13T01 Lu d −26.32
1991−01−14T13 Me e −23.64
1991−01−14T15
** 
B +128.42
1991−01−15T23 Lu c +295.32
1991−01−16T05 Lu xa +298.03
1991−01−18T02 Sa a 10.97
1991−01−18T05 Sa v +297.70
1991−01−18T07 Sa c +297.71
1991−01−24T13 Me xa +282.26
1991−01−25T08 Me d −22.88
1991−01−26T21 Lu +d +26.32
1991−01−28T08 Ju p 4.306
1991−01−28T08 Lu p 0.002420
1991−01−28T08 Lu v +102.03
1991−01−28T19 Ju V +128.61
1991−01−29T00 Ju o +128.58
1991−01−29T06
** 
S +179.87
1991−01−29T10 Lu xd +118.02
1991−01−30T06 Lu o +129.83
1991−02−09T04 Lu V +258.06
1991−02−09T04 Lu a 0.002708
1991−02−09T09 Lu d −26.29
1991−02−12T04
** 
B +138.64
1991−02−12T12 Lu xa +297.99
1991−02−14T17 Lu c +325.54
1991−02−21T20 Pl Rg +230.38
1991−02−22T16 Me a 1.388
1991−02−23T04 Lu +d +26.23
1991−02−25T00 Lu p 0.002457
1991−02−25T06 Lu v +110.05
1991−02−25T19 Lu xd +117.55
1991−02−27T10
** 
S +201.59
1991−02−28T18 Lu o +159.67
1991−03−02T12 Me o +341.76
1991−03−08T17 Lu d −26.14
1991−03−09T00 Lu a 0.002702
1991−03−09T04 Lu V +266.01
1991−03−09T17 Me v +355.70
1991−03−11T18 Lu xa +296.72
1991−03−12T20
** 
B +160.92
1991−03−15T05 Me xd +6.31
1991−03−16T08 Lu c +232.91
1991−03−18T09 Ve xd +29.37
1991−03−21T03 Lu v +62.55
1991−03−22T05 Lu p 0.002473
1991−03−22T10 Lu +d +26.02
1991−03−24T22 Lu xd +115.62
1991−03−27T09 Me e +18.61
1991−03−28T12
** 
S +253.02
1991−03−29T16 Ju +d +20.12
1991−03−30T07 Lu o +189.07
1991−03−30T07 Ma +d +25.37
1991−03−30T12 Ju Pg +123.54
1991−04−02T18
** 
b +125.75
1991−04−04T18 Me Rg +29.02
1991−04−04T21 Me +d +14.17
1991−04−05T01 Lu d −25.89
1991−04−05T20 Lu a 0.002703
1991−04−06T04 Lu V +273.83
1991−04−07T21 Lu xa +294.11
1991−04−11T06
** 
B +187.52
1991−04−13T07 Ur +d −23.08
1991−04−14T19 Lu c +24.35
1991−04−14T20 Me c +24.39
1991−04−15T16 Me V +23.79
1991−04−17T05 Lu v +59.29
1991−04−17T17 Lu p 0.002443
1991−04−18T03 Me p 0.5736
1991−04−18T06 Ur Rg +283.81
1991−04−18T16 Lu +d +25.78
1991−04−18T18 Ne Rg +286.76
1991−04−20T22 Lu xd +112.76
1991−04−22T13 Me xa +19.38
1991−04−22T20 Ne +d −21.59
1991−04−24T07
** 
S +300.87
1991−04−28T09 Me Pg +17.98
1991−04−28T21 Lu o +218.07
1991−05−02T08 Lu d −25.69
1991−05−03T04 Me d +5.21
1991−05−03T14 Lu a 0.002708
1991−05−04T01 Lu V +280.47
1991−05−04T23 Lu xa +291.21
1991−05−06T12
** 
B +209.74
1991−05−10T09 Pl V +228.98
1991−05−10T12 Pl c +228.98
1991−05−10T14
** 
s +138.78
1991−05−10T18 Pl p 28.70
1991−05−11T10 Ve +d +25.92
1991−05−12T14 Sa +d −18.90
1991−05−12T16 Me e −26.01
1991−05−14T04 Lu c +52.90
1991−05−15T09 Lu v +70.98
1991−05−15T16 Lu p 0.002411
1991−05−16T00 Lu +d +25.64
1991−05−17T02 Sa Rg +306.84
1991−05−18T01 Lu xd +110.26
1991−05−18T03
** 
S +253.35
1991−05−27T20
** 
B +223.88
1991−05−28T11 Lu o +246.64
1991−05−29T14 Lu d −25.60
1991−05−31T02 Lu a 0.002713
1991−05−31T14 Lu V +283.78
1991−06−01T02 Lu xa +289.35
1991−06−07T13
** 
S +281.69
1991−06−11T04 Me xd +72.49
1991−06−12T09 Lu +d +25.60
1991−06−12T12 Lu c +81.03
1991−06−12T20 Pl +d −2.27
1991−06−12T20 Lu v +86.30
1991−06−13T00 Lu p 0.002392
1991−06−14T03 Ve e +45.35
1991−06−14T08 Lu xd +109.07
1991−06−16T16 Me v +84.40
1991−06−17T12 Me o +86.21
1991−06−17T16 Me a 1.324
1991−06−21T21 Me +d +24.87
1991−06−22T09
** 
B +175.84
1991−06−25T19 Lu d −25.61
1991−06−27T02 Lu o +275.00
1991−06−27T07 Lu a 0.002716
1991−06−27T13 Lu V +280.07
1991−06−28T07 Lu xa +288.88
1991−07−03T17 Ur p 18.46
1991−07−04T06 Ur o +281.82
1991−07−04T12 Ur V +281.81
1991−07−04T18
** 
S +211.25
1991−07−07T22 Ve xa +147.87
1991−07−08T00 Ne o +285.37
1991−07−08T01 Ne p 29.18
1991−07−08T06 Ne V +285.36
1991−07−09T20 Lu +d +25.63
1991−07−11T09 Lu v +103.01
1991−07−11T10 Lu p 0.002390
1991−07−11T19 Lu xd +108.93
1991−07−11T19 Lu c +108.99
1991−07−19T12 Me xa +142.65
1991−07−19T15
** 
B +140.90
1991−07−23T01 Lu d −25.62
1991−07−24T07 Lu V +274.12
1991−07−24T11 Lu a 0.002714
1991−07−24T22 Me e +27.01
1991−07−25T13 Lu xa +288.97
1991−07−26T18 Lu o +303.26
1991−07−27T00 Sa o +303.50
1991−07−27T01 Sa V +303.50
1991−07−27T04 Sa p 8.947
1991−07−28T19 Pl Pg +227.56
1991−08−01T10 Ve Rg +157.32
1991−08−02T07
** 
S +178.67
1991−08−06T05 Lu +d +25.59
1991−08−07T23 Me Rg +155.90
1991−08−08T05 Lu xd +108.84
1991−08−08T18 Lu p 0.002407
1991−08−08T22 Lu v +119.35
1991−08−10T02 Lu c +137.02
1991−08−10T19
** 
b +109.83
1991−08−11T15 Me d +5.46
1991−08−14T01 Ve d +3.36
1991−08−15T04
** 
B +129.60
1991−08−16T21 Ju v +144.29
1991−08−17T22 Ju c +144.52
1991−08−18T08 Ju a 6.366
1991−08−18T16 Me p 0.6109
1991−08−19T08 Lu d −25.54
1991−08−20T17 Lu V +275.73
1991−08−20T23 Lu a 0.002708
1991−08−21T00 Me V +149.01
1991−08−21T19 Lu xa +288.46
1991−08−21T20 Me c +148.29
1991−08−22T20 Ve c +149.24
1991−08−23T00 Ve V +149.12
1991−08−23T04 Ve p 0.2875
1991−08−25T09 Lu o +331.69
1991−08−29T21
** 
S +179.33
1991−08−31T14 Me Pg +143.05
1991−09−02T12 Lu +d +25.44
1991−09−04T11 Lu xd +107.66
1991−09−05T07
** 
s +114.03
1991−09−05T19 Lu p 0.002438
1991−09−06T01 Me +d +12.87
1991−09−06T05 Lu v +132.72
1991−09−07T04 Me xd +146.08
1991−09−07T17 Me e −18.00
1991−09−08T11 Lu c +165.30
1991−09−12T17
** 
B +127.66
1991−09−13T08 Ve Pg +141.00
1991−09−15T16 Lu d −25.34
1991−09−16T07 Ur d −23.45
1991−09−17T12 Lu V +281.42
1991−09−17T15 Lu a 0.002703
1991−09−17T22 Lu xa +286.58
1991−09−19T05 Ur Pg +279.83
1991−09−23T22 Lu o +20.10
1991−09−24T02 Me v +172.61
1991−09−26T02 Ne Pg +283.98
1991−09−26T06
** 
S +160.66
1991−09−28T03 Ve +d +9.16
1991−09−29T18 Lu +d +25.21
1991−10−01T13 Lu xd +105.15
1991−10−02T17 Lu p 0.002469
1991−10−03T11 Me o +189.64
1991−10−03T13 Lu v +133.58
1991−10−05T02 Sa Pg +300.19
1991−10−06T07 Sa d −20.64
1991−10−06T12 Ne d −21.94
1991−10−07T21 Lu c +194.11
1991−10−11T04
** 
B +106.68
1991−10−11T06 Me a 1.421
1991−10−11T10 Ma a 2.573
1991−10−13T00 Lu d −25.09
1991−10−15T00 Lu xa +283.65
1991−10−15T10 Lu V +288.58
1991−10−15T11 Lu a 0.002702
1991−10−15T11 Me xa +209.84
1991−10−23T11 Lu o +29.53
1991−10−24T20
** 
S +140.47
1991−10−26T23 Lu v +79.18
1991−10−26T23 Lu +d +24.98
1991−10−27T16 Lu p 0.002463
1991−10−28T14 Lu xd +102.23
1991−10−29T02 Ve xd +168.70
1991−11−02T06 Ve e −46.52
1991−11−06T11 Lu c +223.54
1991−11−08T07
** 
B +91.73
1991−11−08T09 Ma c +225.48
1991−11−09T07 Lu d −24.91
1991−11−11T03 Lu xa +281.05
1991−11−12T07 Lu a 0.002706
1991−11−12T10 Lu V +296.13
1991−11−12T15 Pl a 30.64
1991−11−12T21 Pl v +230.29
1991−11−13T12 Pl o +230.31
1991−11−16T10 Ma xa +231.07
1991−11−19T02 Me e +22.24
1991−11−21T07 Me d −25.59
1991−11−21T22 Lu o +59.15
1991−11−22T07
** 
S +129.10
1991−11−23T07 Lu +d +24.86
1991−11−23T19 Lu v +86.53
1991−11−24T02 Lu p 0.002426
1991−11−24T18 Lu xd +100.32
1991−11−28T16 Me Rg +264.19
1991−12−04T03 Me xd +261.55
1991−12−06T03 Lu c +253.50
1991−12−06T09
** 
B +81.41
1991−12−06T14 Lu d −24.85
1991−12−08T08 Lu xa +279.85
1991−12−08T12 Me p 0.6783
1991−12−08T14 Me V +256.04
1991−12−08T14 Me c +256.02
1991−12−10T01 Lu a 0.002713
1991−12−10T06 Lu V +302.32
1991−12−18T02 Me +d −18.77
1991−12−18T11 Me Pg +247.90
1991−12−20T06
** 
S +120.88
1991−12−20T17 Lu +d +24.87
1991−12−21T10 Lu o +89.07
1991−12−22T03 Lu xd +99.83
1991−12−22T05
** 
b +92.62
1991−12−22T08 Lu v +102.96
1991−12−22T09 Lu p 0.002395
1991−12−27T11 Ju d +7.12
1991−12−28T01 Me e −22.14
1991−12−30T20 Ju Rg +164.62



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