icrs_from_app_geo

rubin_sim.utils.icrs_from_app_geo(ra, dec, epoch=2000.0, mjd=None)

Convert the apparent geocentric position in (RA, Dec) to the mean position in the International Celestial Reference System (ICRS)

This method undoes the effects of precession, annual aberration, and nutation. It is meant for mapping pointing RA and Dec (which presumably include the above effects) back to mean ICRS RA and Dec so that the user knows how to query a database of mean RA and Decs for objects observed at a given telescope pointing.

WARNING: This method does not account for apparent motion due to parallax. This means it should not be used to invert the ICRS-to-apparent geocentric transformation for actual celestial objects. This method is only useful for mapping positions on a theoretical celestial sphere.

This method works in degrees.

@param [in] ra in degrees (apparent geocentric). Can be a numpy array or a number.

@param [in] dec in degrees (apparent geocentric). Can be a numpy array or a number.

@param [in] epoch is the julian epoch (in years) of the equinox against which to measure RA (default: 2000.0)

@param [in] mjd is an instantiation of the ModifiedJulianDate class representing the date of the observation

@param [out] a 2-D numpy array in which the first row is the mean ICRS RA and the second row is the mean ICRS Dec (both in degrees)