Theta Eridani (Î¸ Eri, Î¸ Eridani) is a star in the constellation Eridanus. It has the traditional name Acamar from the Arabik Ä€khir an-nahr which means "the end of the riverâ€œ.
Acamar is a double star with some evidence suggesting it is part of a multiple star system
Acamar's distance from Earth as measured by the Hipparcos astrometry satellite is approximately 120 light-years.
Ptolemy described Acamar as a first-magnitude star, which some have taken to be in fact Achernar, which today appears just above the horizon in Alexandria where Ptolemy lived.
Achernar, however, was not visible to Ptolemy (it is from Alexandria today due to procession); its declination in 100CE was -67, making it invisible even at Aswan. Ptolemy's Eridanus thus without doubt ended at Acamar, which rose about 10 degrees above the horizon from Alexandria. This fact besides positively identifying Acamar as the original "end of the river", also strengthens the case for Acamar having been first magnitude in ancient times.
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