Proper motion

Not to be confused with proper velocity or stellar parallax.

Proper motion is the angular speed of a celestial object, such as a star, as it moves across the sky. It is an astrometric measure, giving an object's change in angular position over time relative to the center of mass of the Solar System. This parameter is measured relative to the distant stars or a stable reference such as the International Celestial Reference Frame (ICRF).[1] Patterns in proper motion reveal larger structures like stellar streams, the general rotation of the Milky Way disk, and the random motions of stars in the Galactic halo.[2]

The components for proper motion in the equatorial coordinate system (of a given epoch, often J2000.0) are given in the direction of right ascension (μα) and of declination (μδ). Their combined value is computed as the total proper motion (μ).[3][4] It has dimensions of angle per time, typically arcseconds per year or milliarcseconds per year.

Knowledge of the proper motion, distance, and radial velocity allows calculations of an object's motion from the Solar System's frame of reference and its motion from the galactic frame of reference – that is motion in respect to the Sun, and by coordinate transformation, that in respect to the Milky Way.[5]

  1. ^ Theo Koupelis; Karl F. Kuhn (2007). In Quest of the Universe. Jones & Bartlett Publishers. p. 369. ISBN 978-0-7637-4387-1.
  2. ^ Leeuwen, F. van (2007-11-01). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics. 474 (2): 653–664. arXiv:0708.1752. doi:10.1051/0004-6361:20078357. ISSN 0004-6361.
  3. ^ D. Scott Birney; Guillermo Gonzalez; David Oesper (2007). Observational Astronomy. Cambridge University Press. p. 75. ISBN 978-0-521-85370-5.
  4. ^ Simon F. Green; Mark H. Jones (2004). An Introduction to the Sun and Stars. Cambridge University Press. p. 87. ISBN 978-0-521-54622-5.
  5. ^ D. Scott Birney; Guillermo Gonzalez; David Oesper (2007). Observational Astronomy. Cambridge University Press. p. 73. ISBN 978-0-521-85370-5.
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