This week, two comets, C/2025 A4 and C/2025 R2, are set to make their appearances in the night sky, marking a significant event for stargazers after a year lacking visible comets.
Comet C/2025 A4 will reach its closest approach to Earth on October 21, coming within approximately 56 million miles. Meanwhile, its counterpart, C/2025 R2, known for its striking bluish-green coloration, will pass even closer at roughly 24 million miles. Both comets are expected to exhibit their brightest appearances between October 20 and October 21, with C/2025 A4 being three times more luminous than C/2025 R2.
C/2025 R2, discovered in September 2025 by the Solar and Heliospheric Observatory using the SWAN instrument, will be best viewed a day earlier than C/2025 A4. Observers in the Northern Hemisphere will require binoculars to spot C/2025 R2, while C/2025 A4 will be visible to the naked eye in very dark settings.
On October 21, C/2025 A4 will be most prominently positioned in the northwest sky, close to the Big Dipper and the bright star Arcturus, appearing about an hour and a half after sunset. Conversely, C/2025 R2 will be optimally viewed in the southwest, situated between the bright stars of the Summer Triangle: Vega, Deneb, and Altair.
Notably, astronomers have emphasized the rarity of this event, with C/2025 A4 not expected to return to visibility until the year 3175. Enthusiasts are encouraged to take advantage of this unique opportunity to witness both comets.
As one astronomer noted, “Living in the Northern Hemisphere, I can only admire C/2025 A4 Lemmon so far, but C/2025 R2 SWAN is quickly joining the show and we are ready to amaze every astronomy lover with our live feed!”
