Minor Planet Occultations

(2241) Alcathous on 11 August 2022

(2241) Alcathous is a Jupiter Trojan asteroid, in a 1:1 resonance with Jupiter, stationed at its L₅ Lagrangian point, maintaining position about 60° behind the giant planet. It is estimated to be the 11th largest of the ~10,000 currently known Jupiter Trojans. See its wiki page. It was predicted to occult a 12th mag star on 2022 Aug 11, with Great Shefford Observatory being just south of the shadow, but with estimated positional uncertainties the probability of an occultation was given as 23.5%. Fortunately the actual path was about 36 km further south than the prediction and a short 1.5 s event was recorded by drift-scan. Observation was difficult with the target at an altitude of 17° and with the 100% illuminated full Moon just 32° distant, making the sky background bright and uneven.

Screenshot of drift-scan measurement using Scanalyzer (see page by John Broughton, Reedy Creek Observatory, Australia here).