Stars: Fixed or Moving? | RA, Dec & Julian Date

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SUMMARY

The stars are not fixed in the celestial coordinate system defined by Right Ascension (RA) and Declination (Dec) due to the Earth's axial precession, which occurs over a 26,000-year cycle. This precession causes regular changes in the RA and Dec of stars, necessitating the use of specific equations to account for these shifts. Additionally, each star exhibits its own proper motion, which is the individual movement through space, influenced by its velocity and distance from Earth. Catalogs exist that provide detailed measurements of the proper motion for individual stars.

PREREQUISITES
  • Understanding of celestial coordinate systems, specifically Right Ascension (RA) and Declination (Dec).
  • Familiarity with the concept of axial precession and its implications on celestial navigation.
  • Knowledge of proper motion and its calculation in astrophysics.
  • Access to star catalogs that document proper motion data.
NEXT STEPS
  • Research the equations used to calculate the effects of precession on RA and Dec.
  • Explore the concept of proper motion in detail, including its measurement techniques.
  • Investigate star catalogs such as the Hipparcos or Gaia databases for proper motion data.
  • Learn about the implications of stellar motion on astronomical observations and navigation.
USEFUL FOR

Astronomers, astrophysics students, and anyone interested in celestial navigation and the dynamics of star movements will benefit from this discussion.

Philosophaie
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Are the stars fixed according to RA and Dec? If not is there equations using Julian Date for their movement?
 
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A complex question. RA and Dec are an earth-based coordinate system based on an imaginary projection of the Earth's axis and equator onto the celestial sphere. However, the Earth's axis is not fixed in space, but undergoes a slow "wobble" with a period of about 26,000 years, called precession (http://en.wikipedia.org/wiki/Precession_of_the_equinoxes), So all of the stars change their RA and Dec in a regular way due to this changing of the coordinate system. This is a regular, predictable process and there are equations to compensate for it.

In addition, the stars are moving through space, and each star has its own motion, called proper motion(http://en.wikipedia.org/wiki/Proper_motion), that is determined by how fast it is moving and how far away it is. There are catalogs of the measured proper motion for each star that you can look up if you need to know it.
 

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