ERIDANUS

eridanus, or fluvius ("the river"), in astronomy, a constellation of the southern hemisphere, mentioned by eudoxus (4th century b.c.) and aratus (3rd century b.c.); ptolemy catalogued 34 stars in it. [theta] _eridani_, a fine double star of magnitudes 3.5 and 5.5, is now of the third magnitude. it is supposed to be identical with the _achernar_ of al-sufi, who described it as of the first magnitude; this star has therefore decreased in brilliancy in historic times. the star [omicron]2 _eridani_ (numbered 40 by flamsteed) was discovered to be a ternary star group by herschel in 1783; it consists of a close pair, of magnitudes 9.2 and 10.9, revolving in a period of 180 years, associated with a star of magnitude 4.5, which is distant from the pair by 82"; these stars have an exceptionally swift proper motion, about 4" per annum. eridanus was the ancient name of the river po.