rubin_sim.utils.icrs_from_observed(ra, dec, obs_metadata=None, epoch=None, include_refraction=True)

Convert observed RA, Dec into mean International Celestial Reference Frame (ICRS) RA, Dec. This method undoes the effects of precession, nutation, aberration (annual and diurnal), and refraction. It is meant so that users can take pointing RA and Decs, which will be in the observed reference system, and transform them into ICRS for purposes of querying database tables (likely to contain mean ICRS RA, Dec) for objects visible from a given pointing.

Note: This method is only accurate at angular distances from the sun of greater than 45 degrees and zenith distances of less than 75 degrees.

WARNING: This method does not account for apparent motion due to parallax. This means it should not be used to invert the ICRS-to-observed coordinates 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 is the observed RA in degrees. Can be a numpy array or a number.

@param [in] dec is the observed Dec in degrees. Can be a numpy array or a number.

@param [in] obs_metadata is an ObservationMetaData object describing the telescope pointing.

@param [in] epoch is the julian epoch (in years) against which the mean equinoxes are measured.

@param [in] include_refraction toggles whether or not to correct for refraction

@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)