{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.777","julian_year":2026.777,"time":"2026-10-11T23:19:17.949Z","years_from_j2000":26.777,"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":"m45","name":"Pleiades","class":"open_cluster","category":"cluster","object_type":"Open cluster","mag":1.2,"mag_band":"V","abs_mag":null,"abs_mag_band":null,"distance_ly":444,"distance_method":"literature value (curated)","ra_deg":56.869166666666665,"dec_deg":24.10527777777778,"epoch_ra_deg":57.270148,"epoch_dec_deg":24.188699,"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":"Taurus","discovered":"Antiquity","featured":true,"url":"https://spacecatalog.org/object/m45","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 Seven Sisters: a young open cluster close enough that its brightest members are naked-eye stars, still wrapped in the blue haze of the dust they are drifting through.","properties":{"v_mag":1.2,"redshift":0.000022,"wikidata_id":"Q13423","also_known_as":["SEVEN SISTERS","Seven Sisters"],"ngc_type_code":"OCl","major_axis_arcmin":150,"minor_axis_arcmin":150,"wikipedia_article":"Pleiades","position_angle_deg":90,"radial_velocity_km_s":7},"designations":[{"catalog":"Common name","designation":"Pleiades"},{"catalog":"IAU cluster","designation":"C 0344+239"},{"catalog":"Messier","designation":"M 45"},{"catalog":"MWSC","designation":"MWSC 305"},{"catalog":"OpenNGC","designation":"Mel022"}],"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."}