page_title: Eta Carinae
section_title: Discovery and naming
hierarchical_section_title: Eta Carinae / Observational history / Discovery and naming
caption_attribution_description: English: The lightcurve of Eta Carinae from some of the earliest observations to the current day.
context_page_description: Eta Carinae, formerly known as Eta Argus, is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around 7,500 light-years distant in the constellation Carina. Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel, marking the start of its so-called "Great Eruption". It became the second-brightest star in the sky between 11 and 14 March 1843 before fading well below naked eye visibility after 1856. In a smaller eruption, it reached 6th magnitude in 1892 before fading again. It has brightened consistently since about 1940, becoming brighter than magnitude 4.5 by 2014.
  At declination −59° 41′ 04.26″, Eta Carinae is circumpolar from locations on Earth south of latitude 30°S, and is not visible north of about latitude 30°N.
  The two main stars of the Eta Carinae system have an eccentric orbit with a period of 5.54 years. The primary is a peculiar star similar to a luminous blue variable that was initially 150–250 M☉ of which it has lost at least 30 M☉ already, and is expected to explode as a supernova in the astronomically near future.
context_section_description: There is no reliable evidence of Eta Carinae being observed or recorded before the 17th century, although Dutch navigator Pieter Keyser described a fourth-magnitude star at approximately the correct position around 1595–1596, which was copied onto the celestial globes of Petrus Plancius and Jodocus Hondius and the 1603 Uranometria of Johann Bayer. Frederick de Houtman's independent star catalogue from 1603 does not include Eta Carinae among the other 4th magnitude stars in the region. The earliest firm record was made by Edmond Halley in 1677 when he recorded the star simply as Sequens (i.e. "following" relative to another star) within a new constellation Robur Carolinum. His Catalogus Stellarum Australium was published in 1679. The star was also known by the Bayer designations Eta Roboris Caroli, Eta Argus or Eta Navis. In 1751 Nicolas Louis de Lacaille gave the stars of Argo Navis and Robur Carolinum a single set of Greek letter Bayer designations within his constellation Argo, and designated three areas within Argo for the purposes of using Latin letter designations three times over. Eta fell within the keel portion of the ship which was later to become the constellation Carina. It was not generally known as Eta Carinae until 1879, when the stars of Argo Navis were finally given the epithets of the daughter constellations in the Uranometria Argentina of Gould.
  Eta Carinae is too far south to be part of the mansion-based traditional Chinese astronomy, but it was mapped when the Southern Asterisms were created at the start of the 17th century. Together with s Carinae, λ Centauri, and λ Muscae, Eta Carinae forms the asterism 海山 (Sea and Mountain). Eta Carinae has the names Tseen She (from the Chinese 天社 [Mandarin: tiānshè] "Heaven's altar") and Foramen. It is also known as 海山二 (Hǎi Shān èr, English: the Second Star of Sea and Mountain).
  Halley gave an approximate apparent magnitude of 4 at the time of discovery, which has been calculated as magnitude 3.3 on the modern scale. The handful of possible earlier sightings suggest that Eta Carinae was not significantly brighter than this for much of the 17th century. Further sporadic observations over the next 70 years show that Eta Carinae was probably around 3rd magnitude or fainter, until Lacaille reliably recorded it at 2nd magnitude in 1751. It is unclear whether Eta Carinae varied significantly in brightness over the next 50 years; there are occasional observations such as William Burchell's at 4th magnitude in 1815, but it is uncertain whether these are just re-recordings of earlier observations.
caption: The lightcurve of Eta Carinae from some of the earliest observations to the current day
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