{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.674","julian_year":2026.674,"time":"2026-09-04T02:39:59.441Z","years_from_j2000":26.674,"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":"ngc-3947","name":"NGC 3947","class":"spiral_galaxy_sb","category":"galaxy","object_type":"Spiral galaxy Sb","mag":13.2,"mag_band":"V","abs_mag":null,"abs_mag_band":null,"distance_ly":309477939.81067747,"distance_method":"redshift (CMB frame), flat ΛCDM with H0 = 70 km/s/Mpc","ra_deg":178.33466666666666,"dec_deg":20.751722222222224,"epoch_ra_deg":178.681079,"epoch_dec_deg":20.60233,"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":"Leo","discovered":"1785","featured":false,"url":"https://spacecatalog.org/object/ngc-3947","radius_km":null,"radius_kind":null,"data_quality":null,"description":null,"properties":{"b_mag":13.93,"h_mag":10.52,"j_mag":11.21,"k_mag":10.21,"v_mag":13.2,"redshift":0.0207,"hubble_type":"Sb","wikidata_id":"Q939541","redshift_cmb":0.021795684592441633,"discovered_by":"William Herschel","ngc_type_code":"G","uncertainties":{"distance_ly":[18903219.74645216,18903219.74645216]},"major_axis_arcmin":1.37,"minor_axis_arcmin":0.8,"wikipedia_article":"NGC 3947","position_angle_deg":106,"surface_brightness":22.98,"radial_velocity_km_s":6141},"designations":[{"catalog":"2MASX","designation":"2MASX J11532031+2045055"},{"catalog":"IRAS","designation":"IRAS 11507+2101"},{"catalog":"LEDA","designation":"LEDA 37264"},{"catalog":"MCG","designation":"MCG +04-28-088"},{"catalog":"NGC","designation":"NGC 3947"},{"catalog":"PGC","designation":"PGC 37264"},{"catalog":"SDSS","designation":"SDSS J115320.32+204506.1"},{"catalog":"UGC","designation":"UGC 6863"}],"source":{"id":"openngc","name":"OpenNGC","url":"https://github.com/mattiaverga/OpenNGC","license":"CC-BY-SA-4.0"},"updated_at":"2026-09-02T19:50:56.720Z","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."}