Diurnal Parallax Distances for Near-Sun Objects from the Geostationary Coronagraph GOES-19/CCOR-1

Abstract

Geostationary motion provides a repeating observer baseline that can encode target range in coronagraph images. We apply this to GOES-19/CCOR-1 by registering each frame to field stars and fitting the fixed-phase sidereal-day parallax jointly with smooth sky motion. Thirteen known-distance tracks of planets, asteroids, and comets spanning 0.49–20.5 au yield a median absolute fractional range error of 2.4%; the smallest recovered semiamplitude is 2 .″ 6 (0.13 pixel). A field-star null gives 0 .″ 8, while independently hand-clicked positions reproduce the trend shown by results from automated linker positions. The inferred range also resolves the line-of-sight geometry, correctly placing 3I/ATLAS beyond the Sun and C/2025 R3 between the observer and the Sun. A geostationary coronagraph therefore provides orbit-free line-of-sight information for near-Sun objects inaccessible to ground-based diurnal-parallax programs.