Crater Timings for Jan. 31, 2018, Total Lunar Eclipse Show Umbral Span

Summary: Crater timings for the Jan. 31, 2018, total lunar eclipse show the umbral span by besting limb contacts in predicting Earth's variably sized shadow.

Langrenus Crater in the eastern sector of the moon's Southern Hemisphere is the site of Fred Espenak's final crater timing for the Jan. 31, 2018, total lunar eclipse: Langrenus Crater viewed Dec. 24, 1968, from an altitude of 150 nautical miles by Apollo 8, the first manned mission to the moon: NASA/Apollo 8, Public Domain, via Wikimedia Commons

Crater timings for the Jan. 31, 2018, total lunar eclipse show the umbral span more accurately than suggested lunar limb, or edge, contacts by yielding careful predictions of Earth’s variably sized ecliptic shadow.

Retired NASA astrophysicist Fred Espenak, known as “Mr. Eclipse,” credits Philippe de La Hire (March 18, 1640-April 21, 1718) with discerning that Earth’s umbra displays variably-sized enlargements from one eclipse to the next. In 1702, the French astronomer and mathematician discovered that enlarging the umbra’s radius by one arc minute more than deemed by geometric considerations increases the accuracy of predicted durations of lunar eclipses. One arc minute equals one-sixtieth (1/60) of one degree. One degree represents one-three hundred sixtieth (1/360) of a turn, or full circle.

Earth’s atmosphere influences the umbral enlargement. The process, however, eludes complete understanding as the reason for seemingly variably-sized lunar eclipses remains a mystery.

Careful timings of prominent lunar craters during entrances, termed immersions, into and exits, termed emersions, from the umbra provide clear measurements of a lunar eclipse’s umbral enlargement and yield closely accurate duration predictions for the eclipse’s partiality and totality.

Espenak provides shadow contact timings for lunar eclipses on his dedicated lunar and solar eclipse website, EclipseWise. His table of crater immersion and emersion times for the Wednesday, Jan. 31, 2018, total lunar eclipse tracks umbral contacts with 25 well-defined lunar craters. His predictions for the blue moon total lunar eclipse assumes an approximate atmospherically-induced umbral enlargement of one percent.

Espenak’s calculations begin with Riccioli Crater, located near the western limb in the moon’s Southern Hemisphere. Immersion, or entrance, happens at 11:54 UT. His calculations end with Langrenus, located near the eastern lunar limb in the Southern Hemisphere. Emersion, or exit, happens at 15:05 UT.

The list’s 25 prominent lunar craters are scattered across the western and eastern sectors of both the Northern and Southern Hemispheres of the moon’s near side. Southwestern umbral contact timings comprise five craters:
Billy: 12:03 UT immersion, 14:12 UT emersion;
Campanus: 12:16 UT immersion, 14:22 UT emersion;
Grimaldi: 11:55 UT immersion, 14:12 UT emersion;
Riccioli: 11:54 UT immersion, 14:12 UT emersion;
Tycho: 12:29 UT immersion, 14:26 emersion.

Southeastern umbral contact timings comprise four craters:
Censorinus: 12:32 UT immersion, 14:56 UT emersion;
Goclenius: 12:39 UT immersion, 15:00 UT emersion;
Langrenus: 12:43 UT immersion, 15:05 UT emersion;
Messier: 12:38 UT immersion, 15:02 UT emersion.

Northwestern umbral contact timings consider six craters:
Aristarchus: 11:54 UT immersion, 14:23 UT emersion;
Copernicus: 12:06 UT immersion, 14:32 UT emersion;
Kepler: 11:59 UT immersion, 14:23 UT emersion;
Plato: 12:06 UT immersion, 14:41 UT emersion;
Pytheas: 12:04 UT immersion, 14:33 UT emersion;
Timocharis: 12:06 UT immersion, 14:37 UT emersion.

Northeastern umbral contact timings comprise 10 craters:
Aristoteles: 12:14 UT immersion, 14:49 UT emersion;
Autolycus: 12:11 UT immersion, 14:44 UT emersion;
Dionysius: 12:24 UT immersion, 14:49 UT emersion;
Endymion: 12:23 UT immersion, 14:58 UT emersion;
Eudoxus: 12:15 UT immersion, 14:50 UT emersion;
Manilius: 12:18 UT immersion, 14:47 UT emersion;
Menelaus: 12:20 UT immersion, 14:50 UT emersion;
Plinius: 12:24 UT immersion, 14:54 UT emersion;
Proclus: 12:33 UT immersion, 15:03 UT emersion;
Taruntius: 12:36 UT immersion, 15:03 UT emersion.

Espenak’s summary of the Jan. 31 eclipse suggests times of the event’s major phases based upon lunar limb, or edge, contacts with Earth’s penumbra, or light, outer shadow, and umbra, or dark, inner shadow. Lunar limb contact calculations place the penumbral phase from 10:51:13 Universal Time (UT) to 16:08:32 UT. Partiality begins at 11:48:28 UT and ends at 15:11:14 UT. Totality spans 1 hour 16 minutes 8 seconds, from 12:51:49 to 14:7:57 UT.

Amateur, expert and novice skygazers can record their own timings with two simple tools: a low-power telescope and a watch synchronized with radio time signals. Espenak suggests aiming for a precision of 0.1 minute (six seconds) in timings.

The total lunar eclipse Wednesday, Jan. 31, 2018, occurs as the month’s blue moon. January opens with a full moon, reaching fullness on the month’s second day, and closes with a full moon. In a month with two full moons, the second is designated as a blue moon.

The takeaway for crater timings for the Jan. 31, 2018, total lunar eclipse, which occurs during the month’s blue moon, is that the activity encourages familiarity with lunar features and yields more accurate predictions of eclipse durations.

map of lunar features between 45 north and south latitudes, with Riccioli Crater (site of Fred Espenak's first crater immersion timing) highlighted in blue and Langrenus Crater (site of Fred Espenak's final crater emersion timing) in green: The Defense Mapping Agency Aerospace Center for National Aeronautics and Space Administration (NASA), Public Domain, via NASA Headquarters

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Langrenus Crater in the eastern sector of the moon's Southern Hemisphere is the site of Fred Espenak's final crater timing for the Jan. 31, 2018, total lunar eclipse: Langrenus Crater viewed Dec. 24, 1968, from an altitude of 150 nautical miles by Apollo 8, the first manned mission to the moon: NASA/Apollo 8, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Langrenus_crater_as08-16-2616hr.jpg

map of lunar features between 45 north and south latitudes, with Langrenus Crater highlighted in green and Riccioli Crater highlighted in blue: The Defense Mapping Agency Aerospace Center for National Aeronautics and Space Administration (NASA), Public Domain, via NASA Headquarters @ https://www.hq.nasa.gov/alsj/NASALunarChart.jpg

For further information:

Espenak, Fred. "Crater Timings During Lunar Eclipses." EclipseWise > Lunar Eclipses > Eclipses During 2018 > Total Lunar Eclipse of January 31
Available @ https://eclipsewise.com/oh/oh-help/LEcrater.html

Espenak, Fred. "Table 1: Total Lunar Eclipse of 2018 Jan 31 Crater Immersion and Emersion Times." EclipseWise > Lunar Eclipses > Eclipses During 2018 > Total Lunar Eclipse of January 31.
Available @ https://eclipsewise.com/oh/oh-tables/ec2018-Tab01.pdf

Espenak, Fred. "Total Lunar Eclipse of January 31." EclipseWise > Lunar Eclipses > Eclipses During 2018.
Available @ https://eclipsewise.com/oh/ec2018.html#LE2018Jan31T

La Hire, Philippe de. Tabulae Astronomicae Ludovici Magni Jussu et Munificentia Exaratæ et In Lucem Editæ: In Quibus Solis, Lunæ Reliquorumque Planetarum Motus ex Ipsis Observationibus, Nulla Adhibita Hypothesi, Traduntur; Habenturque Praecipuarum Fixarum in Nostro Horizonte Conspicuarum Positiones; Ineundi Calculi Methos, cum Geometrica Ratione Computandum Eclipsum Sola Triangulorum Rectilineorum Analysi, Breviter Exponitur; Adjecta Svnt Descriptio, Constructio & Vsus Instrumentorum Astronomiae Novae Practicæ Inservientium, Variaque Problemata Astronomis Geographisque Perutilia. Ad Meridianum Observatorii Regii Parisiensis in Quo Habitae Sunt Observationes ab Ipso Autore. Parisiis [Paris, France]: Joannem Boudot [Jean Boudot], M.DCC.II [1702].
Available via HathiTrust @ https://hdl.handle.net/2027/mdp.39015011942300

Marriner, Derdriu. "Blue Moon Month January 2018 Opens New Year With Two Full Moons." Earth and Space News. Wednesday, Dec. 27, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/12/blue-moon-month-january-2018-opens-new.html

Marriner, Derdriu. "Jan. 31, 2018, Blue Moon Total Lunar Eclipse Belongs to Saros Cycle 124." Earth and Space News. Wednesday, Jan. 10, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/01/jan-31-2018-blue-moon-total-lunar.html

NASA Aeronautics and Space Administration. Lunar Chart. NASA Headquarters > Apollo Lunar Surface Journal.
Available @ https://www.hq.nasa.gov/alsj/NASALunarChart.jpg

Sinnott, Roger W. "Useful Projects for a Lunar Eclipse." Sky and Telescope > Astronomy News > Observing News. Feb. 19, 2008.
Available @ http://www.skyandtelescope.com/astronomy-news/observing-news/useful-projects-for-a-lunar-eclipse/