{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.778","julian_year":2026.778,"time":"2026-10-12T00:32:56.082Z","years_from_j2000":26.778,"frame":"date","applied":"Proper motion, then precession and nutation. The catalogued position is carried along the great circle the object's own published motion puts it on, at a constant velocity, from the epoch that position was measured at, 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. The motion runs from position_epoch_jyear where the upstream publishes one — a timed pulsar's position belongs to the year it was timed — and from J2000 where it does not. 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":"m51","name":"Whirlpool Galaxy","class":"intermediate_spiral_galaxy_sabb","category":"galaxy","object_type":"Intermediate spiral galaxy SABb","mag":8.36,"mag_band":"V","abs_mag":null,"abs_mag_band":null,"distance_ly":23600000,"distance_method":"literature value (curated)","ra_deg":202.46962499999998,"dec_deg":47.195166666666665,"epoch_ra_deg":202.754892,"epoch_dec_deg":47.05587,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"position_epoch_jyear":null,"orbits":null,"semi_major_axis_km":null,"periapsis_km":null,"mass_kg":null,"mass_msun":null,"constellation":"Canes Venatici","discovered":"1773","featured":true,"url":"https://spacecatalog.org/object/m51","source":{"id":"openngc","name":"OpenNGC","url":"https://github.com/mattiaverga/OpenNGC","license":"CC-BY-SA-4.0","attribution":"OpenNGC, Mattia Verga (github.com/mattiaverga/OpenNGC). Fields derived from it stay under CC BY-SA 4.0.","commercial_use":"allowed"},"radius_km":null,"radius_kind":null,"data_quality":null,"description":"The first galaxy ever seen to have spiral structure, locked in a gravitational dance with a smaller companion that lights up its arms with newborn stars.","properties":{"b_mag":8.61,"h_mag":5.65,"j_mag":6.4,"k_mag":5.5,"v_mag":8.36,"redshift":0.00155,"hubble_type":"SABb","wikidata_id":"Q13957","redshift_cmb":0.0021269775971712868,"discovered_by":"Charles Messier","ngc_type_code":"G","major_axis_arcmin":13.71,"minor_axis_arcmin":11.67,"wikipedia_article":"Whirlpool Galaxy","position_angle_deg":163,"surface_brightness":22.9,"radial_velocity_km_s":465},"designations":[{"catalog":"2MASX","designation":"2MASX J13295269+4711429"},{"catalog":"Common name","designation":"Whirlpool Galaxy"},{"catalog":"IRAS","designation":"IRAS 13277+4727"},{"catalog":"IRAS","designation":"IRAS F13277+4727"},{"catalog":"LEDA","designation":"LEDA 47404"},{"catalog":"MCG","designation":"MCG +08-25-012"},{"catalog":"Messier","designation":"M 51"},{"catalog":"NGC","designation":"NGC 5194"},{"catalog":"PGC","designation":"PGC 47404"},{"catalog":"UGC","designation":"UGC 8493"}],"updated_at":"2026-10-01T09:42:28.932Z","attribution":"Data from SpaceCatalog.org. Each record names its upstream in `source`, with that producer's terms in `source.license`, the acknowledgement it asks for in `source.attribution`, and whether its terms allow commercial use in `source.commercial_use`; those terms govern the record, and citing SpaceCatalog does not discharge them."}