{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.680","julian_year":2026.68,"time":"2026-09-06T11:49:01.340Z","years_from_j2000":26.68,"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":"hat-p-21-b","name":"HAT-P-21 b","class":"gas_giant","category":"exoplanet","object_type":"Gas giant","mag":null,"mag_band":null,"abs_mag":null,"abs_mag_band":null,"distance_ly":904.3598810054319,"distance_method":"NASA Exoplanet Archive sy_dist (TICv8, 2019AJ....158..138S)","ra_deg":171.2749348,"dec_deg":41.0280207,"epoch_ra_deg":171.640388,"epoch_dec_deg":40.880462,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"orbits":"HAT-P-21","semi_major_axis_km":7535244.747159,"periapsis_km":null,"mass_kg":9.243913132356054e+27,"mass_msun":0.0046489,"constellation":"Ursa Major","discovered":"2010","featured":false,"url":"https://spacecatalog.org/object/hat-p-21-b","radius_km":79356.25641900001,"radius_kind":null,"data_quality":null,"description":null,"properties":{"host_star":"HAT-P-21","host_v_mag":11.459,"eccentricity":0.23,"uncertainties":{"mass_kg":[2.980070558069611e+27,2.980070558069611e+27],"radius_km":[11438.739664,11438.739664],"distance_ly":[10.254356515414413,10.4859275435933],"eccentricity":[0.02,0.02],"host_mass_solar":[0.6,0.6],"inclination_deg":[0.7,0.7],"host_radius_solar":[0.17,0.17],"host_temperature_k":[80,80],"semi_major_axis_km":[100230.57336899999,100230.57336899999],"orbital_period_days":[0.000007,0.000007],"argument_of_periastron_deg":[1.9,2.1]},"host_mass_solar":1.24,"inclination_deg":87.2,"stars_in_system":1,"discovery_method":"Transit","host_radius_solar":1.21,"planets_in_system":1,"discovery_facility":"HATNet","host_spectral_type":"G3","host_temperature_k":5588,"orbital_period_days":4.12448,"transit_midpoint_bjd":2458159.89639,"equilibrium_temperature_k":1367,"argument_of_periastron_deg":305.8},"designations":[{"catalog":"Exoplanet","designation":"HAT-P-21 b"},{"catalog":"Host star","designation":"HAT-P-21"}],"source":{"id":"exoplanet_archive","name":"NASA Exoplanet Archive (Planetary Systems Composite Parameters)","url":"https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView?app=ExoTbls&config=PSCompPars","license":"Public domain (NASA)"},"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."}