Apparent place

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The apparent place of an object is the position in space as seen by the observer. Because of physical and/or geometrical effects it has a deviation from the "true position".

In astronomy the term "apparent places of stars" means the visual or photographic position of the star, as seen from the moving Earth. For instance, its speed of 30 km per second around the Sun causes an annual aberration of about 20" (10−4 rad) because the Earth's velocity is about 0.01 percent of the speed of light.

Other effects are the parallax (different angle to the star during the year), or the daily aberration because of the Earth's rotation, and the Earth's precession - a monotonic changing of the direction of the Earth's axis, which causes an analogous slow turning of the coordinate systems which we use on Earth and in space.

The "Apparent Places of Fundamental Stars" (commonly abbreviated APFS) is an astronomical yearbook, which is published one year in advance by the Astronomisches Rechen-Institut 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.

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