{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.836","julian_year":2026.836,"time":"2026-11-02T07:12:04.956Z","years_from_j2000":26.836,"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":"ngc-4539","name":"NGC 4539","class":"spiral_galaxy_sa","category":"galaxy","object_type":"Spiral galaxy Sa","mag":12.05,"mag_band":"V","abs_mag":null,"abs_mag_band":null,"distance_ly":73006692.3283097,"distance_method":"redshift (CMB frame), flat ΛCDM with H0 = 70 km/s/Mpc","ra_deg":188.64475000000002,"dec_deg":18.202694444444443,"epoch_ra_deg":188.983827,"epoch_dec_deg":18.053837,"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":"Coma Berenices","discovered":"1831","featured":false,"url":"https://spacecatalog.org/object/ngc-4539","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":null,"properties":{"b_mag":12.91,"h_mag":9.61,"j_mag":10.37,"k_mag":9.45,"v_mag":12.05,"redshift":0.00416,"hubble_type":"Sa","wikidata_id":"Q1112371","redshift_cmb":0.005205885602208582,"discovered_by":"John Frederick William Herschel","ngc_type_code":"G","uncertainties":{"distance_ly":[14338469.631581815,14338469.631581815]},"major_axis_arcmin":2.74,"minor_axis_arcmin":1.08,"position_angle_deg":94,"surface_brightness":23.46,"radial_velocity_km_s":1245},"designations":[{"catalog":"2MASX","designation":"2MASX J12343476+1812092"},{"catalog":"LEDA","designation":"LEDA 41839"},{"catalog":"MCG","designation":"MCG +03-32-071"},{"catalog":"NGC","designation":"NGC 4539"},{"catalog":"PGC","designation":"PGC 41839"},{"catalog":"SDSS","designation":"SDSS J123434.73+181209.6"},{"catalog":"UGC","designation":"UGC 7735"}],"updated_at":"2026-10-01T09:42:28.932Z","citation":{"plain":"SpaceCatalog. NGC 4539 [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/ngc-4539","bibtex":"@misc{spacecatalog_ngc-4539,\n  author       = {{SpaceCatalog}},\n  title        = {{NGC 4539}},\n  howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},\n  year         = {2026},\n  url          = {https://spacecatalog.org/object/ngc-4539},\n  note         = {Catalogue entry, data release DR1 (2026-08-21). Values from OpenNGC.}\n}","url":"https://spacecatalog.org/object/ngc-4539","release":"DR1","doi":null},"references":[],"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."}