{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.672","julian_year":2026.672,"time":"2026-09-03T11:51:19.186Z","years_from_j2000":26.672,"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":"hd-21931","name":"HD 21931","class":"b9v_blue_white_main_sequence_star","category":"star","object_type":"B9V blue-white main-sequence star","mag":7.35,"mag_band":"V","abs_mag":0.266,"abs_mag_band":"V","distance_ly":851.5832129015748,"distance_method":"parallax","ra_deg":53.55399,"dec_deg":48.617462,"epoch_ra_deg":54.033828,"epoch_dec_deg":48.707381,"epoch_moved_arcsec":0.984,"pm_ra_mas_yr":18.71,"pm_dec_mas_yr":-31.81,"orbits":null,"semi_major_axis_km":null,"periapsis_km":null,"mass_kg":null,"mass_msun":null,"constellation":"Perseus","discovered":null,"featured":false,"url":"https://spacecatalog.org/object/hd-21931","radius_km":null,"radius_kind":null,"data_quality":null,"description":null,"properties":{"wds_id":"03342+4837","companions":[{"measured":2016,"magnitude":11.9,"components":"AB","discoverer_code":"BU  787","separation_arcsec":5.2,"position_angle_deg":293},{"measured":2016,"magnitude":11.75,"components":"AD","discoverer_code":"BU  787","separation_arcsec":34.5,"position_angle_deg":181},{"measured":2015,"magnitude":8.81,"components":"AE","discoverer_code":"ARN  57","separation_arcsec":175.2,"position_angle_deg":29}],"mass_solar":2.652,"radius_solar":1.974,"spectral_type":"B9V","color_index_bv":0.038,"luminosity_solar":68.17105263058534,"radial_velocity_km_s":-4.9,"spectral_type_source":"SIMBAD (2024A&A...690A.176N, quality C)","surface_gravity_log_g":4.17,"surface_temperature_k":11130,"proper_motion_ra_mas_yr":18.71,"proper_motion_dec_mas_yr":-31.81,"stellar_parameters_method":"Gaia DR3 model fit (GSP-Phot, FLAME; RUWE ≤ 1.4) — low confidence: above 7,500 K GSP-Phot's temperature and extinction are degenerate","bolometric_luminosity_solar":53.3681},"designations":[{"catalog":"HD","designation":"HD 21931"},{"catalog":"HIP","designation":"HIP 16649"}],"source":{"id":"hyg","name":"HYG Database v4.1","url":"https://github.com/astronexus/HYG-Database","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."}