Mensa

IAU Mensa chart (CC0)

Mensa, originally "Mons Mensae" (Table Mountain), is one of the 88 IAU constellations. There were no ancient (Babylonian, Greek or Roman) constellations in this area, so early modern astronomers created names in the southern hemisphere. The region has no bright stars, the brightest star α Mensae is 5.1 mag, and has thus not been subject to any (?)gestalt-seeing(?).

Etymology and History

Table Mountain with table cloth (cloud) called "Cape Cloud" (SMH 2024).

In the 1750s, the French surveyor and mathematician Nicolas-Louis de Lacaille was based in the trading station at the South African Cape of Good Hope that has developed into the city of Cape Town. He lived there for two years and measured positions of the land and the stars. In gaps of historical constellations, he invented new ones and named them after contemporary devices such as drawing tools, telescope, microscope, and a pendulum clock. The constellation of the Table Mountain seems to stand out as it is named after a geographical feature in Cape Town's landscape. However, Lacaille's reason is preserved in his 1756 report for the French Academy of Science.

Enfin, j’ai mis au dessous du grand nuage la Montagne de la Table, célèbre au cap de Bonne-espérance par sa figure de table, et principalement par un nuage blanc qui la vient couvrir en forme de nappe à l’approche d’un vent violent de sud-est; d’ailleurs la pluspart des Navigateurs appellent nuages du Cap, ce que nous appelons nuées de Magellan, ou le grand et le petit nuage.

English

Finally, I have placed below the large cloud the Table Mountain, famous at the Cape of Good Hope for its table-like shape, and mainly for a white cloud which covers it in the form of a tablecloth when a strong south-easterly wind approaches; moreover, most navigators call the Cape Clouds what we call Magellan's Clouds, or the Large and Small Clouds.

Illustration of the "Größeren Kapwolke" (‘Greater Cape Cloud’) in the ‘Bilderatlas der Sternenwelt’ by E. Weiss (1892).

There are two easily recognisable, free-standing dwarf galaxies in the southern sky. Today, they are generally called the Magellanic Clouds (even though there is now an initiative to ask the IAU to rename them because Magellan, as a European explorer, did not always behave nicely towards the indigenous people he met - and they ended up having their own names for these celestial objects, which they were well aware of). In Lacaille's time, however, this was not yet firmly established terminology and so the Frenchman suggested that the Large Magellanic Cloud be called the ‘Cape Cloud’.

"Cape Cloud" was the term with which navigators of the ocean-going ships referred to the cloud above the Table Mountain in Cape Town. Due to a weather rule, the mountain and its cloud had an instrumental function: Lacaille quotes a weather rule of the navigators, according to which a white cloud like a tablecloth on Table Mountain, before a dangerous south-easterly wind arises.

Images of the Table Mountain

A view of the Cape of Good Hope, taken on the Spot, from on board the Resolution, Capt. Cook, Oil on canvas (William Hodges 1772, CC0).

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  Table Mountain in Cape Town without its Cloud (SMH, August 2024)

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  Table Mountain in Cape Town with its Cloud (SMH, August 2024)

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  Table Mountain in Cape Town with its Cloud (SMH, August 2024)

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  Table Mountain in Cape Town with its Cloud (SMH, August 2024)

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  Table Mountain, Cape Town, South Africa (Bruno Wolff 2017, CC0)

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  View of Table Mountain from Orange Street, Cape Town, Western Cape, South Africa (CC By Dietmar Rabich).

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  Table Mountain in Cape Town with its Cloud (SMH, August 2024)

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  Table Mountain in Cape Town with its Cloud (SMH, August 2024)

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  Cape Town mountains from above their clouds (SMH, August 2024); the layer is rather thin and attached to the mountains.

Historical Images in Star Charts

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  Lacaille's constellation Mensa in his French Planisphere (1756) (CC0)

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  Mons Mensae in Lacaille's map Coelum australe stelliferum (1763): Zurich Library

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  Constellation Mensa in Bode's Uranographia 1801 (CC0)

IAU WGSN Catalog of Star Names

By the occasion of the IAU GA in Cape Town 2024, it was proposed to name the (yet nameless) main star of the constellation Mensa with an Indigenous term for the mountain. Thus, it was proposed to use the term "Hoerikwaggo" from San language (Khoekhoe: Huriǂoaxa, lit. 'sea-emerging'). The term literally means "Sea Mountain" and is perhaps the earliest known (written) name for this mountain, published in 1779 already.

Sources:

• Robert Gordon 1779
• John Barrows 1797 ; cited by Nienaber and Raper 1977: 560
• Gabriel Stefanus Nienaber, P. E. Raper (1983): "Hottentot (Khoekhoen) Place Names"

Astrophysics of Alpha Mensae (HIP 29271, HR 2261, HD 43834):

• observation: (a) in the TESS Continuous Viewing Zone, and (b) is one of the nearest, brightest stars subject to asteroseismologic analysis with TESS (Chontos+ 2021; SIMBAD)
• From asteroseismology, the age is fairly well-constrained age of 6 Gyr. It also has an M dwarf companion at 3".
• Alpha Men was also one of the 164 provisional target stars for the Habitable Worlds Observatory that Karl Stapelfeldt and Eric Mamajek (2023). They are mostly naked eye FGK-type dwarfs within about 20 parsecs, and Alpha Mensae is a G7V at 10 parsecs and it should make for a great HWO target for the search for Earth-like planets (so long as the light of the companion star can be mitigated!).

Weblinks

• Ridpath, Ian, "Star Tales: online edition".

References

• References (general)
• References (Babylonian)
• References (ancient Greco-Roman)
• References (medieval)