Epsilon Eridani - Observation History

Observation History

Epsilon Eridani, the Bayer designation for this star, was established in 1603 as part of the Uranometria, a star catalogue produced by German celestial cartographer Johann Bayer. His catalogue assigned letters from the Greek alphabet to groups of stars belonging to the same visual magnitude class in each constellation, beginning with alpha (α) for a star in the brightest class. However, Bayer made no attempt to arrange stars by relative brightness within each class. Thus, although Epsilon is the fifth letter in the Greek alphabet, the star is the tenth brightest star in Eridanus. The star catalogue of English astronomer John Flamsteed, published in 1712, gave this star the Flamsteed designation 18 Eridani as it was the eighteenth catalogued star in the constellation of Eridanus by order of increasing right ascension. In 1918 this star appeared in the Henry Draper Catalogue with the designation HD 22049 and a preliminary spectral classification of K0.

Based on observations between 1800 and 1880, Epsilon Eridani was found to have a large proper motion across the celestial sphere, which was estimated at an angular velocity of three arcseconds annually. This movement implied it was relatively close to the Sun, making it a star of interest for the purpose of trigonometric parallax measurements. This process involves recording the position of the star as the Earth moves around the Sun, which allows the star's distance to be estimated. From 1881 to 1883, American astronomer William L. Elkin used a heliometer at the Royal Observatory at the Cape of Good Hope, South Africa to compare the position of Epsilon Eridani with two nearby stars. From these observations, a parallax of 0.14 ± 0.02 arcseconds was calculated. By 1917, observers had refined their parallax estimate to 0.317 arcseconds. The modern value of 0.3109 arcseconds is equivalent to a distance of about 10.50 ly (3.22 parsecs).