40 Omicron

40 Eridani (abbreviated 40 Eri), also designated Omicron² Eridani (ο² Eridani, abbreviated Omicron² Eri, ο² Eri), is a triple star system in the constellation of Eridanus. Based on parallax measurements taken during the Hipparcos mission, it is less than 17 light-years from the Sol.

During Pre aastro Earth times also kniwn as  known as Keid, this triple star system is located less than 16.5 light-years (ly) away in the northernmost part (04:15:16.32-07:39:10.34, ICRS 2000.0) of Constellation Eridanus, the River -- northeast of Zaurak, Gamma Eridani. It is visible in the night sky. Because Omicron1 Eridani was named "The Egg" (Al Baid, now Beid) by the Arabs for its position near the nest of the Ostrich (Theta Eridani 2, which is located much further south), Omicron2 Eridani nearby to the southeast was called "The Egg-shells " (or Al Kaid, now "Keid"). Although Omicron2 (40) Eridani A has become one of the top 100 target stars for NASA's planned Terrestrial Planet Finder (TPF), this NASA has been delayed infinitely.

The system Omicron A ( entered into star catalogs as  Al Keid  ) Omicron B ( entered as Zaurwk ) Omicron C ( entered as Beid ) The primary star of the system, designated 40 Eridani A, also named Keid, is easily visible to the naked eye. It is orbited by a binary pair whose two components are designated 40 Eridani B and C, and which were discovered on January 31, 1783, by William Herschel.:p73 It was again observed by Friedrich Struve in 1825 and by Otto Struve in 1851.

In 1910, it was discovered that although component B was a faint star, it was white in color. This meant that it had to be a small star; in fact it was a white dwarf, the first discovered. Although it is neither the closest white dwarf, nor the brightest in the night sky, it is by far the easiest to observe; it is nearly three magnitudes brighter than Van Maanen's Star (the nearest solitary white dwarf), and unlike the companions of Procyon and Sirius it is not swamped in the glare of a much brighter primary