Fixed Stars in the Chart
They are called fixed because, against the background of the planets, they barely move: their proper motion is just fractions of an arcsecond per year. Yet the entire sphere of stars slowly shifts due to axial precession-about 50.3 arcseconds per year, or 1 degree every 72 years.
Therefore, star coordinates are always given for a specific epoch. Regulus moved from Leo to Virgo around 2012, and Spica is now at 24° Libra. A catalog without an epoch date is unusable.
- •Precession: 50.3 arcseconds per year, 1 degree every 72 years
- •Coordinates are always tied to the calculation epoch.
- •Proper motion of a star is negligible compared to precession.