There's a bit of a historical mystery surrounding the star Theta Eridani. Ptolemy in the second century A.D. and al-Sufi in A.D. 964 both recorded Theta Eridani as one of the 13 brightest stars in the sky. Hipparchus may have said the same. But there's a problem. For it to be one of the 13 brightest , it had to be much more luminous than it is today. ...read more read less