How do you convert to "Of Date" or "Apparent" coordinates from "J2000" coordinates? The website: http://ssd.jpl.nasa.gov/horizons.cgi#results there are two options for displaying RA and DEC: Astrometric and Apparent. Astrometric is the J2000 coordinates and Apparent is the "Of Date". http://www.ephemeris.com/goto.php Just lists the Apparent www.stellarium.org software Lists both "Of Date" and J2000 coordinates. My question is: Is there a formula to convert between the two coordinate systems?