Noun
any star in the Ptolemaic theory of planetary motion
Source: WordNetHe also compared the lengths of the tropical year (the time it takes the Sun to return to an equinox) and the sidereal year (the time it takes the Sun to return to a fixed star), and found a slight discrepancy. Source: Internet
On both occasions, Galileo mistook Neptune for a fixed star when it appeared very close—in conjunction—to Jupiter in the night sky, hence, he is not credited with Neptune's discovery. Source: Internet
This suggested it was not even a planet, but a fixed star in the stellar sphere beyond all the planets. Source: Internet