From decf9a25605b98f3a73e419d5d6063a76a5b2beb Mon Sep 17 00:00:00 2001 From: Merlin Fisher-Levine Date: Fri, 1 Nov 2024 08:48:37 -0700 Subject: [PATCH] Add function for getting ecliptic coordinates --- python/lsst/summit/utils/utils.py | 51 +++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/python/lsst/summit/utils/utils.py b/python/lsst/summit/utils/utils.py index 4e2b9659..4399f951 100644 --- a/python/lsst/summit/utils/utils.py +++ b/python/lsst/summit/utils/utils.py @@ -1258,3 +1258,54 @@ def getCameraFromInstrumentName(instrumentName: str) -> lsst.afw.cameraGeom.Came case _: raise ValueError(f"Unsupported instrument: {instrumentName}") return camera + + +def calcEclipticCoords(ra: float, dec: float) -> tuple[float, float]: + """Get the ecliptic coordinates of the specified ra and dec. + + Transform J2000 (ra, dec), both in degrees, to + IAU1976 Ecliptic coordinates (also returning degrees). + + Matches the results of: + + from astropy.coordinates import SkyCoord, HeliocentricEclipticIAU76 + import astropy.units as u + + p = SkyCoord(ra=ra0*u.deg, dec=dec0*u.deg, distance=1*u.au, frame='hcrs') + ecl = p.transform_to(HeliocentricEclipticIAU76) + print(ecl.lon.value, ecl.lat.value) + + except that it's fast. + + Parameters + ---------- + ra : `float` + The right ascension, in degrees. + dec : `float` + The declination, in degrees. + + Returns + ------- + lambda : `float` + The ecliptic longitude in degrees. + beta : `float` + The ecliptic latitude in degrees. + """ + + ra, dec = np.deg2rad(ra), np.deg2rad(dec) + + # IAU 1976 obliquity + epsilon = np.deg2rad(23.43929111111111) + cos_eps, sin_eps = np.cos(epsilon), np.sin(epsilon) + + sra, cra = np.sin(ra), np.cos(ra) + sdec, cdec = np.sin(dec), np.cos(dec) + + lambda_ = np.arctan2((sra * cos_eps + sdec / cdec * sin_eps), cra) + beta = np.arcsin(sdec * cos_eps - cdec * sin_eps * sra) + + # normalize + if lambda_ < 0: + lambda_ += np.pi * 2 + + return (np.rad2deg(lambda_), np.rad2deg(beta))