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{{Short description|Partial lunar eclipse in 1991}}
{{Infobox lunar eclipse
| type = partial
| image = Lunar eclipse chart close-1991Dec21.png
| caption = The Moon's hourly motion shown right to left
| date = December 21, 1991
| gamma = 0.9709
| magnitude = 0.0876
| saros_ser = 115
| saros_no = 56 of 72
| partiality = 64 minutes, 4 seconds
| penumbral = 251 minutes, 29 seconds
| p1 = 8:27:18
| u1 = 10:01:02
| greatest = 10:33:01
| u4 = 11:15:06
| p4 = 12:38:46
| previous = July 1991
| next = June 1992
}}
A partial [[lunar eclipse]] occurred at the Moon’s [[Lunar node|descending node]] of orbit on Saturday, December 21, 1991,<ref>{{cite web|title=December 20–21, 1991 Partial Lunar Eclipse|url=https://www.timeanddate.com/eclipse/lunar/1991-december-21|publisher=timeanddate|access-date=8 January 2025}}</ref> with an umbral [[Magnitude of eclipse|magnitude]] of 0.0876. A lunar eclipse occurs when the [[Moon]] moves into the [[Earth's shadow]], causing the Moon to be darkened. A partial lunar eclipse occurs when one part of the Moon is in the Earth's umbra, while the other part is in the Earth's penumbra. Unlike a [[solar eclipse]], which can only be viewed from a relatively small area of the world, a lunar eclipse may be viewed from anywhere on the [[night]] side of Earth. Occurring only about 23 hours before [[Apsis|perigee]] (on December 22, 1991, at 9:25 UTC), the Moon's apparent diameter was larger.<ref>{{cite web|title=Moon Distances for London, United Kingdom, England|url=https://www.timeanddate.com/astronomy/moon/distance.html?year=1991&n=136|publisher=timeanddate|access-date=8 January 2025}}</ref>

This eclipse was the last of four lunar eclipses in 1991, with the others occurring on [[January 1991 lunar eclipse|January 30]] (penumbral), [[June 1991 lunar eclipse|June 27]] (penumbral), and [[July 1991 lunar eclipse|July 26]] (penumbral).

== Visibility ==
The eclipse was completely visible over [[northeast Asia]], much of [[North America]], and much of the [[Pacific Ocean]], seen rising over [[central Asia|central]], [[south Asia|south]], and [[east Asia]], and [[Australia]] and setting over [[South America]] and [[northern Europe]].<ref>{{cite web|title=Partial Lunar Eclipse of 1991 Dec 21|url=https://eclipse.gsfc.nasa.gov/LEplot/LEplot1951/LE1991Dec21P.pdf|publisher=NASA|access-date=8 January 2025}}</ref>

{| class=wikitable
|[[File:Lunar eclipse from moon-1991Dec21.png|300px]] [[File:Lunar eclipse chart close-1991Dec21.png|300px]]
|}

== Eclipse details ==
Shown below is a table displaying details about this particular solar eclipse. It describes various parameters pertaining to this eclipse.<ref>{{cite web|title=Partial Lunar Eclipse of 1991 Dec 21|url=https://eclipsewise.com/lunar/LEprime/1901-2000/LE1991Dec21Pprime.html|publisher=EclipseWise.com|access-date=8 January 2025}}</ref>

{|class="wikitable" align="{{{align|left}}}" style="margin:{{#ifeq:{{{align}}}|right|0 0 0.5em 1em|0 1em 0.5em 0}}"
|+December 21, 1991 Lunar Eclipse Parameters
! Parameter
! Value
|-
| Penumbral Magnitude
| 1.06511
|-
| Umbral Magnitude
| 0.08762
|-
| Gamma
| 0.97094
|-
| Sun Right Ascension
| 17h55m52.1s
|-
| Sun Declination
| -23°26'13.9"
|-
| Sun Semi-Diameter
| 16'15.5"
|-
| Sun Equatorial Horizontal Parallax
| 08.9"
|-
| Moon Right Ascension
| 05h56m15.5s
|-
| Moon Declination
| +24°25'15.3"
|-
| Moon Semi-Diameter
| 16'38.0"
|-
| Moon Equatorial Horizontal Parallax
| 1°01'02.6"
|-
| ΔT
| 58.3 s
|}
{{clear}}

== Eclipse season ==
{{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]].

{| class="wikitable"
|+ Eclipse season of December 1991–January 1992
! December 21 Descending node (full moon) !! [[Solar eclipse of January 4, 1992|January 4]] Ascending node (new moon) 
|-
| [[File:Lunar eclipse chart close-1991Dec21.png|200px]] || [[File:SE1992Jan04A.png|200px]]
|- align=center
| [[Lunar eclipse#Types of lunar eclipse|Partial lunar eclipse]] Lunar Saros 115 || [[Total eclipse#Types|Annular solar eclipse]] Solar Saros 141
|}

== Related eclipses ==
=== Eclipses in 1991 ===
* [[Solar eclipse of January 15, 1991|An annular solar eclipse on January 15]].
* [[January 1991 lunar eclipse|A penumbral lunar eclipse on January 30]].
* [[June 1991 lunar eclipse|A penumbral lunar eclipse on June 27]].
* [[Solar eclipse of July 11, 1991|A total solar eclipse on July 11]].
* [[July 1991 lunar eclipse|A penumbral lunar eclipse on July 26]].
* '''A partial lunar eclipse on December 21.'''

=== Metonic ===
* Preceded by: [[March 1988 lunar eclipse|Lunar eclipse of March 3, 1988]]
* Followed by: [[October 1995 lunar eclipse|Lunar eclipse of October 8, 1995]]

=== Tzolkinex ===
* Preceded by: [[November 1984 lunar eclipse|Lunar eclipse of November 8, 1984]]
* Followed by: [[January 1999 lunar eclipse|Lunar eclipse of January 31, 1999]]

=== Half-Saros ===
* Preceded by: [[Solar eclipse of December 15, 1982]]
* Followed by: [[Solar eclipse of December 25, 2000]]

=== Tritos ===
* Preceded by: [[January 1981 lunar eclipse|Lunar eclipse of January 20, 1981]]
* Followed by: [[November 2002 lunar eclipse|Lunar eclipse of November 20, 2002]]

=== Lunar Saros 115 ===
* Preceded by: [[December 1973 lunar eclipse|Lunar eclipse of December 10, 1973]]
* Followed by: [[December 2009 lunar eclipse|Lunar eclipse of December 31, 2009]]

=== Inex ===
* Preceded by: [[January 1963 lunar eclipse|Lunar eclipse of January 9, 1963]]
* Followed by: [[November 2020 lunar eclipse|Lunar eclipse of November 30, 2020]]

=== Triad ===
* Preceded by: [[February 1905 lunar eclipse|Lunar eclipse of February 19, 1905]]
* Followed by: [[October 2078 lunar eclipse|Lunar eclipse of October 21, 2078]]

=== Lunar eclipses of 1991–1994 ===
{{Lunar eclipse set 1991-1994}}

=== Metonic series ===
{{Metonic lunar eclipse 1991-2048}}

=== Saros 115 ===
{{Lunar Saros series 115}}

=== Tritos series ===
{{Lunar Tritos series November 2002}}

=== Inex series ===
{{Lunar Inex series November 2020}}

=== Half-Saros cycle===
A lunar eclipse will be preceded and followed by solar eclipses by 9 years and 5.5 days (a [[Saros (astronomy)#Relationship between lunar and solar saros .28sar.29|half saros]]).<ref>Mathematical Astronomy Morsels, Jean Meeus, p.110, Chapter 18, ''The half-saros''</ref> This lunar eclipse is related to two partial solar eclipses of [[Solar Saros 122]].
{| class=wikitable
![[Solar eclipse of December 15, 1982|December 15, 1982]]
![[Solar eclipse of December 25, 2000|December 25, 2000]]
|-
|[[File:SE1982Dec15P.png|240px]]
|[[File:SE2000Dec25P.png|240px]]
|}

== See also ==
*[[List of lunar eclipses]]
*[[List of 20th-century lunar eclipses]]

==References==
{{reflist}}

== External links ==
* [http://www.hermit.org/eclipse/gen_stats.cgi?mode=query&page=full&qtype=type&body=L&saros=115 Saros cycle 115]
* {{LEplot1951 link|1991|Dec|21|P}}

{{Lunar eclipses}}

{{DEFAULTSORT:Lunar eclipse 1991-12}}
[[Category:20th-century lunar eclipses|1991-12]]
[[Category:1991 in science]]
[[Category:December 1991]]

December 1991 lunar eclipse - Revision history

imported>BunnysBot: /* Eclipse season */ Fix CW Errors with GenFixes (T1)