A penumbral

lunar eclipse A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, ...

occurred at the Moon’s

descending node An orbital node is either of the two points where an orbit intersects a plane of reference to which it is inclined. A non-inclined orbit, which is contained in the reference plane, has no nodes. Planes of reference Common planes of referenc ...

of orbit on Thursday, August 18, 2016, with an umbral

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of −0.9925. A lunar eclipse occurs when the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

moves into the

Earth's shadow Earth's shadow (or Earth shadow) is the shadow that Earth itself casts through its atmosphere and into outer space, toward the antisolar point. During the twilight period (both early dusk and late dawn), the shadow's visible fringe – someti ...

, 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 A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the view of the Sun from a small part of Earth, totally or partially. Such an alignment occurs approximately every six months, during the eclipse season i ...

, which can only be viewed from a relatively small area of the world, a lunar eclipse may be viewed from anywhere on the

night Night, or nighttime, is the period of darkness when the Sun is below the horizon. Sunlight illuminates one side of the Earth, leaving the other in darkness. The opposite of nighttime is daytime. Earth's rotation causes the appearance of ...

side of Earth. Occurring about 3.4 days before

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

(on August 21, 2016, at 21:20 UTC), the Moon's apparent diameter was larger. The HM National Almanac Office's online canon of eclipses lists this event as the last eclipse on Saros Series 109, while NASA lists August 8, 1998 as the last eclipse of the series, and has this event missing the shadow. 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 Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

and ending at 9:59. This produced a maximum penumbral magnitude of 0.0166. Eclipses of such small magnitudes are visually imperceptible; a penumbral magnitude of approximately 0.6 is required for even skilled observers to detect.

Background

The Earth's penumbral shadow is larger than would be expected from simple geometry, a phenomenon first observed by

Philippe de La Hire Philippe de La Hire (or Lahire, La Hyre or Phillipe de La Hire) (18 March 1640 – 21 April 1718)

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. 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. In 1989,

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

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 The ''Connaissance des temps'' (English: Knowledge of the Times) is an official yearly publication of astronomical ephemerides in France. Until just after the French Revolution, the title appeared as ''Connoissance des temps'', and for several ye ...

'' used more conservative assumptions about the size of the Earth's shadow and did not predict an eclipse to occur at all. The ''

Bureau des Longitudes __NOTOC__ The ''Bureau des Longitudes'' () is a French scientific institution, founded by decree of 25 June 1795 and charged with the improvement of nautical navigation, standardisation of time-keeping, geodesy and astronomical observation. Durin ...

'' in France continued to refine their lunar eclipse models; NASA's 2009 edition of its lunar eclipse almanac was based on their values, which effectively reclassified nine eclipses between 1801 and 2300 as non-events, including the one in August 2016. Some resources, including the

HM Nautical Almanac Office His Majesty's Nautical Almanac Office (HMNAO), now part of the United Kingdom Hydrographic Office, was established in 1832 on the site of the Royal Observatory, Greenwich (ROG), where ''The Nautical Almanac'' had been published since 1767. HMNAO ...

'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 AccuWeather, Inc. is a private-sector American media company that provides commercial weather forecasting services. AccuWeather was founded in 1962 by Joel N. Myers. The company adopted the name 'AccuWeather' in 1971. AccuWeather is headquar ...

reported the upcoming eclipse and projected this was the final member of

Lunar Saros 109 Saros cycle series 109 for lunar eclipses occurred at the moon's descending node, 18 years 11 and 1/3 days. It contained either 71 or 72 events, depending on multiple calculation Summary Lunar Saros series 109, repeating every 18 years and 11 days, ...

Visibility

The eclipse was completely visible over

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography. Etymology T ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

, and

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

, seen rising over western Australia and

northeast Asia Northeast Asia or Northeastern Asia is a geographical Subregion#Asia, subregion of Asia. Its northeastern landmass and islands are bounded by the Pacific Ocean, North Pacific Ocean. The term Northeast Asia was popularized during the 1930s by Ame ...

and setting over eastern North and South America.

Eclipse season

This eclipse is part of an

eclipse season An eclipse season is a period, roughly every six months, when eclipses occur. Eclipse seasons are the result of the axial parallelism of the Orbit of the Moon, Moon's orbital plane (orbital inclination, tilted five degrees to the ecliptic, Earth ...

, 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 A fortnight is a unit of time equal to 14 days (two weeks). The word derives from the Old English term , meaning "" (or "fourteen days", since the Anglo-Saxons counted by nights). Astronomy and tides In astronomy, a ''lunar fortnight'' is hal ...

. The first and last eclipse in this sequence is separated by one

synodic month In lunar calendars, a lunar month is the time between two successive Syzygy (astronomy), syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona people, S ...