A penumbral lunar eclipse occurred at the Moon’s descending node of orbit on Thursday, August 18, 2016,[1] with an umbral magnitude of −0.9925. A lunar eclipse occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. A penumbral lunar eclipse occurs when part or all of the Moon's near side passes into 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 about 3.4 days before perigee (on August 21, 2016, at 21:20 UTC), the Moon's apparent diameter was larger.[2]
| Penumbral eclipse | |||||||||
 The Moon barely clipped the northern penumbral shadow of the Earth. | |||||||||
| Date | August 18, 2016 | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Gamma | 1.559 | ||||||||
| Magnitude | −0.9925 | ||||||||
| Saros cycle | 109 (72 of 72) | ||||||||
| Penumbral | 33 minutes, 36 seconds | ||||||||
| |||||||||
The HM National Almanac Office's online canon of eclipses lists this event as the last eclipse on Saros Series 109,[3] while NASA lists August 8, 1998 as the last eclipse of the series, and has this event missing the shadow.[4]
This eclipse grazed the northern boundary of the Earth's penumbral shadow. The event lasted 33 minutes and 36 seconds, beginning at 9:25 UTC and ending at 9:59. This produced a maximum penumbral magnitude of 0.0166.[5] Eclipses of such small magnitudes are visually imperceptible; a penumbral magnitude of approximately 0.6 is required for even skilled observers to detect.[6]
Background
editThe Earth's penumbral shadow is larger than would be expected from simple geometry, a phenomenon first observed by Philippe de La Hire in 1707. The precise amount of enlargement varies over time for reasons which are not fully understood, but likely involve the amount of dust in certain layers of the Earth's atmosphere.[7] Various eclipse almanacs have used different assumptions about the magnitude of this effect, resulting in disagreement about the predicted duration of lunar eclipses or, in the case of penumbral eclipses of very short duration, whether the eclipse will occur at all.[8]
In 1989, NASA published a lunar eclipse almanac that predicted a short penumbral lunar eclipse to occur on 18 August 2016. However, the French almanac Connaissance des Temps used more conservative assumptions about the size of the Earth's shadow and did not predict an eclipse to occur at all.[8] The Bureau des Longitudes in France continued to refine their lunar eclipse models; NASA's 2009 edition of its lunar eclipse almanac was based on their values,[9] which effectively reclassified nine eclipses between 1801 and 2300 as non-events, including the one in August 2016.[a][10]
Some resources, including the HM Nautical Almanac Office's online canon of eclipses, continued to list the 18 August 2016 event. Despite not appearing in NASA's printed lists of eclipses since the 2009 revision, AccuWeather reported the upcoming eclipse and projected this was the final member of Lunar Saros 109.[11]
Visibility
editThe eclipse was completely visible over Australia, North and South America, and Antarctica, seen rising over western Australia and northeast Asia and setting over eastern North and South America.[12]
|
Hourly motion shown right to left |
Eclipse season
editThis 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. The first and last eclipse in this sequence is separated by one synodic month.
| August 18 Descending node (full moon) |
September 1 Ascending node (new moon) |
September 16 Descending node (full moon) |
|---|---|---|
| |
 |
|
| Penumbral lunar eclipse Lunar Saros 109 |
Annular solar eclipse Solar Saros 135 |
Penumbral lunar eclipse Lunar Saros 147 |
Related eclipses
editEclipses in 2016
edit- A total solar eclipse on March 9.
- A penumbral lunar eclipse on March 23.
- A penumbral lunar eclipse on August 18.
- An annular solar eclipse on September 1.
- A penumbral lunar eclipse on September 16.
Metonic
edit- Followed by: Lunar eclipse of June 5, 2020
Tzolkinex
edit- Preceded by: Lunar eclipse of July 7, 2009
Tritos
edit- Followed by: Lunar eclipse of July 18, 2027
Lunar Saros 109
edit- Preceded by: Lunar eclipse of August 8, 1998
Inex
edit- Preceded by: Lunar eclipse of April 14, 1987
- Followed by: Lunar eclipse of March 3, 2045
Triad
edit- Followed by: Lunar eclipse of June 20, 2103
Lunar eclipses of 2016–2020
edit| Lunar eclipse series sets from 2016–2020 | ||||||||
|---|---|---|---|---|---|---|---|---|
| Descending node | Ascending node | |||||||
| Saros | Date | Type Viewing |
Gamma | Saros | Date Viewing |
Type Chart |
Gamma | |
| 109 | 2016 Aug 18
|
Penumbral
|
1.56406 | 114
|
2017 Feb 11
|
Penumbral
|
−1.02548 | |
119
|
2017 Aug 07
|
Partial
|
0.86690 | 124
|
2018 Jan 31
|
Total
|
−0.30143 | |
129_(43696968392)_(cropped).jpg)
|
2018 Jul 27
|
Total
|
0.11681 | 134_(cropped).jpg)
|
2019 Jan 21
|
Total
|
0.36842 | |
139
|
2019 Jul 16
|
Partial
|
−0.64300 | 144
|
2020 Jan 10
|
Penumbral
|
1.07270 | |
| 149 | 2020 Jul 05
|
Penumbral
|
−1.36387 | |||||
| Last set | 2016 Sep 16 | Last set | 2016 Mar 23 | |||||
| Next set | 2020 Jun 05 | Next set | 2020 Nov 30 | |||||
Saros 109
editAccording to some sources, this was the last lunar eclipse of Saros cycle 109, and was eclipse 72 in that series.[5] There are many ways to determine the boundaries of Earth's shadow. One model was revised and this eclipse was classified a non-event by that model. Some eclipse sites decided to follow those calculations which meant Saros 109 now includes 71 events, with the last occurring on 8 August 1998.[4]
See also
editNotes
edit- ^ The others are: 22 April 1864, 21 June 1872, 26 October 1882, 21 February 1951, 28 October 2042, 7 March 2194, 30 April 2219, and 18 February 2288.
References
edit- ^ "August 18, 2016 Almost Lunar Eclipse". timeanddate. Retrieved 16 November 2024.
- ^ "Moon Distances for London, United Kingdom, England". timeanddate. Retrieved 16 November 2024.
- ^ "Penumbral Eclipse of the Moon: 2016 August 18". Canon of Eclipses. HM Nautical Almanac Office. 22 June 2018. Archived from the original on 31 October 2018. Retrieved 11 January 2019.
- ^ a b "Catalog of Lunar Eclipse Saros Series: Saros Series 109". NASA Eclipse Web Site. Retrieved 11 January 2019.
- ^ a b Espenak 1989, p. 150.
- ^ Espenak & Meeus 2009, p. 11.
- ^ Espenak 1989, p. 205.
- ^ a b Espenak 1989, p. 207.
- ^ Espenak & Meeus 2009, p. v.
- ^ Espenak & Meeus 2009, p. 10.
- ^ Sutherland, Scott (17 August 2016). "An 'almost, maybe' lunar eclipse this week?". The Weather Network. Retrieved 10 January 2019.
- ^ "III. Penumbral Eclipse of the Moon" (PDF). HM Nautical Almanac Office. Retrieved 16 November 2024.
Bibliography
edit- Espenak, Fred (1989). Fifty Year Canon of Lunar Eclipses: 1986–2035 (PDF). NASA. NASA Reference Publication 1216.
- Espenak, Fred; Meeus, Jean (2009). Five Millennium Catalog of Lunar Eclipses: -1999 to +3000 (2000 BCE to 3000 CE) (PDF). NASA. NASA/TP-2009-213173.