Constellation | |
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Abbreviation | Men |
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Genitive | Mensae |
Pronunciation | /ˈmɛnsə/ genitive: /ˈmɛnsiː/ |
Symbolism | the Table Mountain |
Right ascension | 03h 12m 55.9008s - 07h 36m 51.5289s |
Declination | −71° - −85.5° |
Quadrant | SQ1 |
Area | 153 sq. deg. (75th) |
Main stars | 4 |
Bayer/Flamsteed stars | 16 |
Stars with planets | 3 |
Stars brighter than 3.00m | 0 |
Stars within 10.00 pc (32.62 ly) | 0 |
Brightest star | α Men (5.09m) |
Messier objects | 0 |
Meteor showers | 0 |
Bordering constellations | Chamaeleon Dorado Hydrus Octans Volans |
Visible at latitudes between +4° and −90°. Best visible at 21:00 (9 p.m.) during the month of January. |
Mensa is a constellation in the Southern Celestial Hemisphere near the south celestial pole, one of fourteen constellations drawn up in the 18th century by French astronomer Nicolas-Louis de Lacaille. Its name is Latin for table, though it originally commemorated Table Mountain and was known as "Mons Mensae". One of the eighty-eight constellations designated by the International Astronomical Union (IAU), it covers a keystone-shaped wedge of sky 153.5 square degrees in area. Other than the south polar constellation of Octans, it is the most southerly of constellations and is observable only south of the 5th parallel of the Northern Hemisphere.
One of the faintest constellations in the night sky, Mensa contains no apparently bright stars—the brightest, Alpha Mensae, is barely visible in suburban skies. Part of the Large Magellanic Cloud, several star clusters and a quasar lie in the area covered by the constellation, and at least three of its star systems have been found to have exoplanets.
Originally named "Montagne de la Table" or "Mons Mensae",[1] Mensa was created by Nicolas-Louis de Lacaille out of dim Southern Hemisphere stars in honor of Table Mountain, a South African mountain overlooking Cape Town, near the location of Lacaille's observatory. He recalled that the Magellanic Clouds were sometimes known as Cape clouds, and that Table Mountain was often covered in clouds when a southeasterly stormy wind blew. Hence he made a "table" in the sky under the clouds.[2] Lacaille had observed and catalogued 10,000 southern stars during a two-year stay at the Cape of Good Hope. He devised 14 new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. Mensa was the only constellation that did not honor an instrument symbolic of the Age of Enlightenment.[3] Sir John Herschel proposed shrinking the name to one word in 1844, noting that Lacaille himself had abbreviated some of his constellations thus.[4]
Although the stars of Mensa do not feature in any ancient mythology, the mountain it is named after has a rich mythology. Called "Tafelberg" in Dutch and German, it has two neighboring mountains called "Devil's Peak" and "Lion's Head". Table Mountain features in the mythology of the Cape of Good Hope, notorious for its storms. Explorer Bartolomeu Dias saw the mountain as a mythical anvil for storms.
Mensa is bordered by Dorado to the north, Hydrus to the northwest and west, Octans to the south, Chamaeleon to the east and Volans to the northeast. Covering 153.5 square degrees and 0.372% of the night sky, it ranks 75th of the 88 constellations in size.[5] The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is "Men".[6] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of eight segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 03h 12m 55.9008s and 07h 36m 51.5289s, while the declination coordinates are between −69.75° and −85.26°.[7] The whole constellation is visible to observers south of latitude 5°N.[5][a]
See also: List of stars in Mensa |
Lacaille gave eleven stars in the constellation Bayer designations, using the Greek alphabet to label them Alpha through to Lambda Mensae (excluding Kappa). Gould later added Kappa, Mu, Nu, Xi and Pi Mensae. Stars as dim as these were not generally given designations; however, Gould felt their closeness to the South Celestial Pole warranted their naming.[2] Alpha Mensae is the brightest star with a barely visible apparent magnitude of 5.09,[8] making it the only constellation with no star above magnitude 5.0.[9] Overall, there are 22 stars within the constellation's borders brighter than or equal to apparent magnitude 6.5.[b][5]
The Large Magellanic Cloud lies partially within Mensa's boundaries,[44] although most of it lies in neighbouring Dorado.[9] It is a satellite galaxy of the Milky Way, located at a distance of 163,000 light-years.[45] Among its stars within Mensa are W Mensae, an unusual yellow-white supergiant that belongs to a rare class of star known as a R Coronae Borealis variable,[46] HD 268835, a blue hypergiant that is girded by a vast circumstellar disk of dust,[47] and R71, a luminous blue variable star that brightened in 2012 to over a million times as luminous as the Sun.[48] Also within the galaxy is NGC 1987, a globular cluster estimated to be around 600 million years old that has a significant number of red ageing stars,[49] and NGC 1848, a 27 million year old open cluster.[50] Mensa contains several described open clusters, most of which can be only be clearly observed from large telescopes.[51]
PKS 0637-752 is a distant quasar with a calculated redshift of z = 0.651. It was chosen as the first target of the then newly-operational Chandra X-Ray Observatory in 1999. The resulting images revealed a gas jet approximately 330,000 light-years long. It is visible at radio, optical and x-ray wavelengths.[52]