{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.664","julian_year":2026.664,"time":"2026-08-31T14:48:48.802Z","years_from_j2000":26.664,"frame":"date","applied":"Proper motion, then precession and nutation. The catalogued J2000 position is carried along the great circle the object's own published motion puts it on, at a constant velocity, and the result is referred to the true equator and equinox of this instant. Those are separate things: the motion moves the object, and the rotation turns the grid under it by about fifty arcseconds a year, with nutation adding up to another seventeen.","excluded":"Parallax, the radial-velocity perspective term, aberration and refraction; each is below the accuracy of the catalogued positions themselves. An object with no published proper motion comes back where the catalogue has it rather than at a fabricated zero, and says so with a null pm_ra_mas_yr. A body with no fixed position is not propagated at all — its place comes from an ephemeris, which is what /api/v1/visible answers with."},"slug":"m91","name":"M91","class":"spiral_galaxy_sb","category":"galaxy","object_type":"Spiral galaxy Sb","mag":10.96,"mag_band":"V","abs_mag":null,"abs_mag_band":null,"distance_ly":38014673.616747424,"distance_method":"redshift (CMB frame), flat ΛCDM with H0 = 70 km/s/Mpc","ra_deg":188.86020833333333,"dec_deg":14.496333333333332,"epoch_ra_deg":189.198735,"epoch_dec_deg":14.348366,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"orbits":null,"semi_major_axis_km":null,"periapsis_km":null,"mass_kg":null,"mass_msun":null,"constellation":"Coma Berenices","discovered":"1781","featured":false,"url":"https://spacecatalog.org/object/m91","radius_km":null,"radius_kind":null,"data_quality":null,"description":null,"properties":{"b_mag":10.94,"h_mag":7.37,"j_mag":8.01,"k_mag":7.12,"v_mag":10.96,"redshift":0.001644,"hubble_type":"Sb","wikidata_id":"Q14344","redshift_cmb":0.002715838901578449,"discovered_by":"Charles Messier","ngc_type_code":"G","uncertainties":{"distance_ly":[14090557.414520642,14090557.414520642]},"major_axis_arcmin":5.55,"minor_axis_arcmin":4.52,"wikipedia_article":"Messier 91","position_angle_deg":150,"surface_brightness":23.24,"radial_velocity_km_s":492},"designations":[{"catalog":"2MASX","designation":"2MASX J12352642+1429467"},{"catalog":"IRAS","designation":"IRAS 12328+1446"},{"catalog":"IRAS","designation":"IRAS F12329+1446"},{"catalog":"LEDA","designation":"LEDA 41934"},{"catalog":"MCG","designation":"MCG +03-32-075"},{"catalog":"Messier","designation":"M 91"},{"catalog":"NGC","designation":"NGC 4548"},{"catalog":"PGC","designation":"PGC 41934"},{"catalog":"SDSS","designation":"SDSS J123526.45+142946.8"},{"catalog":"UGC","designation":"UGC 7753"}],"source":{"id":"openngc","name":"OpenNGC","url":"https://github.com/mattiaverga/OpenNGC","license":"CC-BY-SA-4.0"},"updated_at":"2026-08-30T09:56:50.739Z","attribution":"Data from SpaceCatalog.org. Individual records carry their source and license in `source`; attribution is required for CC-BY and CC-BY-SA rows."}