Precession and Proper MotionApplet

Precession and Proper Motion Applet

Input field: green
Use Enter or Return key to enter the next input field.
Uncheck the box "Dec>=0" for a negative declination value.

Algorithm from J. Meeus ("Astronomical Algorithms", Chapter 20: Precession).

The current standard epoque is "J2000" (2000, Jan 1 at 12 h TD), corresponding to JD 2 451 545.0. For purposes of calculating positions of stars, the beginning of a "year" differs from the standard epoque J2000.0 by an integer multiple of the Julian year (365.25 days).

Noon on January 1, -4712, i.e., January 1, 4713 BC (JD 0) is J-4711.96441

mean tropical year 365.24219 SI days

Example:
(Meeus: Astronomical Algorithms, p. 127)

In case the proper motion in RA is given in seconds (s), the value has to be multiplied by 15 to get arcseconds (as)
(e.g. 0.03425 s = 513.75 mas)

The results of my applet agree with the results of Meeus:
RA = 2h 46m 11.331s, dec = 49° 20' 54.54''

The coordinates (Ra, Dec) are also converted to ecliptic values (long. L, lat. B)

Updated: 2007 Jan 22