The previous month has seen Comet C/2025 A6 (Lemmon) brightening quickly forward of its shut method to the solar, resulting in rising pleasure that it may shine brightly sufficient to be seen by the bare eye in mid-late October.
Solar system comets are likely to change into more and more energetic and shiny within the weeks and months main as much as perihelion — their closest method to the solar in a given orbit — and Comet Lemmon is not any exception. Heat and power from the solar vaporizes the comet’s icy deposits, reworking them right into a gaseous central coma and tail that drags dusty particles together with it, which mirror daylight and create the dramatic spectacles we see by telescopes or within the evening sky.
Read on to find the place and when to search for Comet Lemmon earlier than, throughout and after its flyby of Earth on Oct. 21.
Magnitude
Magnitude is the size used to measure the obvious brightness of objects within the evening sky. The decrease the quantity, the brighter the thing! For context, the brightest stars are round Mag +1, whereas a full moon is -13 and the solar is -27.
Comet Lemmon has brightened from magnitude +21.5 upon its discovery in January to roughly +5.7, in response to the Comet Observation Database (COBS) maintained by the Crni Vrh Observatory in Slovenia. That technically locations it above the +6 detection restrict of the human eye in good darkish sky situations, although the sunshine solid by the waning gibbous moon will add an additional barrier to visibility within the week forward.
If Comet Lemmon continues its present brightening development, it may change into a good looking, hazy bare eye goal within the coming weeks, with its mild changing into simpler to outline by a pair of binoculars, or a yard telescope.
Much like the planets and the moon, Comet Lemmon is constantly shifting relative to the stars beyond. Mid-October will see the wandering body pass close to the star Alkaphrah, or Chi Ursae Majoris in the constellation Ursa Major, just below the ‘dipper’ portion of the Big Dipper asterism, before beating a path through the night sky towards the star Cor Caroli in the constellation Canes Venatici.
Comet Lemon will be in the heart of the constellation Boötes, the Herdsman, as it makes its closest approach to Earth on Oct. 21, before travelling on to pass beneath the head of the great serpent represented in the constellation Serpens on Oct. 26 to 27.
The optimal hour to search for the comet will shift depending on the time of the month in which you are looking. Comet Lemmon will be positioned high above the northeastern horizon in the hours preceding dawn in early October, but will have transitioned to the evening sky by the time it makes its close approach to Earth on Oct. 21, when it will appear low on the northwestern horizon.
Interested in capturing Comet Lemmon with a camera for yourself? Then be sure to read our guide on how to image a comet, along with our picks of the best cameras and lenses available for astrophotography in 2025. Amateur astronomers should also check out our roundups of the best telescopes and binoculars for viewing the night sky.
Editor’s Note: If you would like to share your astrophotography with Space.com’s readers, then please send your photo(s), comments, and your name and location to spacephotos@space.com.