{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.653","julian_year":2026.653,"time":"2026-08-27T16:19:37.891Z","years_from_j2000":26.653,"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":"m17","name":"Checkmark Nebula","class":"nebula","category":"nebula","object_type":"Nebula","mag":7,"mag_band":"V","abs_mag":null,"abs_mag_band":null,"distance_ly":5500,"distance_method":"literature value (curated)","ra_deg":275.19629166666664,"dec_deg":-16.17152777777778,"epoch_ra_deg":275.583426,"epoch_dec_deg":-16.159791,"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":"1745","featured":true,"url":"https://spacecatalog.org/object/m17","radius_km":null,"radius_kind":null,"data_quality":null,"description":"One of the brightest and most massive star-forming regions in the galaxy, its glowing bar of gas shaped like the swan it is named for.","properties":{"b_mag":6,"v_mag":7,"redshift":-0.000149,"wikidata_id":"Q11357","also_known_as":["Horseshoe Nebula","Lobster Nebula","Swan Nebula"],"discovered_by":"Jean-Philippe de Cheseaux","ngc_type_code":"Neb","major_axis_arcmin":12.6,"wikipedia_article":"Omega Nebula","radial_velocity_km_s":-45},"designations":[{"catalog":"Common name","designation":"Checkmark Nebula"},{"catalog":"Common name","designation":"Lobster Nebula"},{"catalog":"Common name","designation":"omega Nebula"},{"catalog":"Common name","designation":"Swan Nebula"},{"catalog":"HD","designation":"HD 168520"},{"catalog":"IAU cluster","designation":"C 1817-162"},{"catalog":"LBN","designation":"LBN 60"},{"catalog":"Lynds","designation":"LBN 015.28-00.67"},{"catalog":"Messier","designation":"M 17"},{"catalog":"MWSC","designation":"MWSC 2896"},{"catalog":"NGC","designation":"NGC 6618"}],"source":{"id":"openngc","name":"OpenNGC","url":"https://github.com/mattiaverga/OpenNGC","license":"CC-BY-SA-4.0"},"updated_at":"2026-08-27T16:03:54.983Z","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."}