{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.665","julian_year":2026.665,"time":"2026-08-31T18:25:01.044Z","years_from_j2000":26.665,"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":"m18","name":"M18","class":"open_cluster","category":"cluster","object_type":"Open cluster","mag":6.9,"mag_band":"V","abs_mag":null,"abs_mag_band":null,"distance_ly":4873.754752221297,"distance_method":"Gaia DR2 cluster membership (Cantat-Gaudin+ 2020)","ra_deg":274.99370833333336,"dec_deg":-17.101972222222223,"epoch_ra_deg":275.383524,"epoch_dec_deg":-17.090769,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"orbits":null,"semi_major_axis_km":null,"periapsis_km":null,"mass_kg":null,"mass_msun":null,"constellation":"Sagittarius","discovered":"1764","featured":false,"url":"https://spacecatalog.org/object/m18","radius_km":null,"radius_kind":null,"data_quality":null,"description":null,"properties":{"b_mag":7.24,"v_mag":6.9,"redshift":-0.000047,"wikidata_id":"Q11370","discovered_by":"Charles Messier","ngc_type_code":"OCl","major_axis_arcmin":6,"wikipedia_article":"Messier 18","distance_reference":"NGC 6613","radial_velocity_km_s":-14},"designations":[{"catalog":"IAU cluster","designation":"C 1817-171"},{"catalog":"Messier","designation":"M 18"},{"catalog":"MWSC","designation":"MWSC 2892"},{"catalog":"NGC","designation":"NGC 6613"}],"source":{"id":"openngc","name":"OpenNGC","url":"https://github.com/mattiaverga/OpenNGC","license":"CC-BY-SA-4.0"},"updated_at":"2026-08-30T09:56:50.739Z","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."}