Several effects cause the apparent position to differ from the mean position:[1] The Apparent Places of Fundamental Stars is an astronomical yearbook, which is published one year in advance by the Astronomical Calculation Institute (Heidelberg University) in Heidelberg, Germany.
It lists the apparent place of about 1000 fundamental stars for every 10 days and is published as a book and in a more extensive version on the Internet.
The apparent position of a planet or other object in the Solar System is also affected by light-time correction, which is caused by the finite time it takes light from a moving body to reach the observer.
Theoretically, light-time correction could also be calculated for more distant objects, such as stars, but in practice it is ignored.
Unlike planets, these objects basically appear to move in straight lines, so for normal use no complicated calculation is needed to find their mean position.