Overview

• Comet Swan reaches its closest approach on October 20 at about 38 million kilometers, appearing low after dusk in northwest Argentina and likely requiring binoculars or a small telescope.
• Comet Lemmon (C/2025 A6) makes its nearest pass on October 21 at roughly 89 million kilometers and is forecast to be viewable from the Northern Hemisphere but not from Argentina.
• Interstellar object 3I/ATLAS, discovered in July, will pass at more than 200 million kilometers and is not expected to be visible from Earth.
• Provenance is confirmed: Swan was detected September 10 by the SWAN instrument aboard NASA’s SOHO, Lemmon was found from Mount Lemmon/Steward Observatory, and 3I/ATLAS was identified by the ATLAS survey.
• Final visibility depends on intrinsic brightness, viewing geometry and local light pollution, so optical aids and dark skies will improve the chances of a sighting.