Apparent place

Apparent place is a term used in astronomy to describe the coordinates of stars or other celestial bodies as seen from Earth, taking into account the effects of aberration and nutation, but not parallax. The apparent place of a star is different from its mean place, which does not take these effects into account.

Definition

The apparent place of a star is its position in the sky as seen from Earth, taking into account the effects of aberration and nutation. Aberration is the apparent shift in the position of a celestial body due to the motion of the observer, while nutation is a small irregularity in the precession of the Earth's axis. Both of these effects can cause a star's apparent place to differ from its mean place.

Calculation

The calculation of a star's apparent place involves several steps. First, the star's mean place is determined from its right ascension and declination, which are measured from a reference point known as the vernal equinox. The effects of aberration and nutation are then added to these coordinates to obtain the star's apparent place.

Use in Astronomy

The concept of apparent place is important in astronomy because it allows astronomers to accurately point their telescopes at celestial bodies. By knowing the apparent place of a star, for example, an astronomer can ensure that their telescope is correctly aligned to observe that star.

See Also

• Astronomical coordinates
• Star position
• Celestial navigation

References

• Astronomy: A Physical Perspective, Marc L. Kutner, Cambridge University Press, 2003.
• Practical Astronomy with your Calculator or Spreadsheet, Peter Duffett-Smith and Jonathan Zwart, Cambridge University Press, 2011.