251102 - C/2025 A6 Comet "Lemmon"
ASTRO:
type=comet
mag=3.5
const=(var.)
dist=55 M mi.
IMAGE:
location=Emerald Bay community, Lake Palestine, TX
BrtlCls=4
exposure=CMOS OSC; 84x10s (14m), G100
palette=LRGB
EQUIPMENT:
optics=ES102CF APO / Starizona "L" 0.65x rdcr, FL(eff.)=464mm, f(eff.)/4.55
camera=ZWO ASI2600MC-Pro
filter=Optolong L-Pro LPS
mount=Celestron AVX
guiding=Orion 60x240mm, ZWO ASi224MC
SOFTWARE:
acquisition=Stellarium, NINA, PHD2
processing=PixInsight, Photoshop (RCAstro, APF-R, WebSharp-Pro), LrC
click image to enlarge
C/2025 A6 (Lemmon) was a non-periodic comet discovered by the Mount Lemmon Observatory Team in images obtained on 3 January 2025. Mount Lemmon is located in the Santa Catalina Mountains northeast of Tuscon, AZ, USA. The discovery was made while participating in the ongoing Mount Lemmon sky survey project. The team made the discovery as they studied images captured from Lemmon's 60 inch cassegrain reflector telescope.
The A6 Lemmon comet was initially classified as an asteroid with an apparent magnitude of about 21.5 in images obtained when it was appx 418 M miles away. Consequently, precovery images were also found in the library of images captured by the PanSTARRS survey dating from 12 November 2024. However, by 21 February 2025, the object had developed a very definite, condensed coma, thereby separating it from the asteroid classification, and cementing it into the recorded annals of comets. It measured appx 2.2 arc-seconds across, with a short tail appx two arc-seconds long. Lemmon's inbound path was carefully measured, and used to calculate its orbital period. Those calculations indicate it will not return for appx 1,350 years. At that periodic frequency, and extrapolating back thru time, its previous perihelion (closest approach to our Sun) would have occurred in the second half of the 7th century, ...during the time of Pythagoras. It will not return again until the year 3175. Composed of ice, dust and rock, its mane appears with a greenish cyan hue due to the presence of diatomic carbon (C2) and cyanogen (CN). Those compounds glow with the characteristic green-cyan color of most comets as they react with radiation and the solar wind emanating from our Sun. The comet made its closest approach to Earth on 21 October 2025 at a distance of appx 55 M miles before achieving perihelion with the Sun. On 3 November 2025 (the day after this image was captured), scientists recorded an apparent magnitude of appx 4.3, and that it was visible to the naked eye and in binoculars in the constellation of Ophiuchus near the globular cluster Messier 12 (M12). When first discovered the comet was expected to only brighten to apparent magnitude 10, resulting in Lemmon's classification as little more than a "minor" comet. Consequently, it didn't do much to capture the attention of the amateur astrophotography (AP) community. But in late October it lit-up brightly, became readily visible and developed a very beautiful, elongated ion tail. It ultimately brightened to an actual apparent magnitude 3.5, which made it about 400 times brighter than originally predicted. That's when the AP community "woke-up". ...literally hundreds of extremely remarkable and beautiful images started pouring-in thru online forums; and the name "Lemmon" quickly became a mainstay. IMAGER'S COMMENTS:Due to a definite lack of forethought, your Host almost missed it. The techniques required to capture a respectable image of a comet are very unique and complex, and therefore challenging. Considerable forethought, planning and preparation are required. Other comets have been captured and included in this collection: 2020 F3 "Neowise" 2021 A1 "Leonard" 2022 E3 (ZTF) "Bolin-Masci" 2023 A3 "Tsuchinshan-ATLAS" But all of these were captured using "single-shot" techniques with a DSLR camera & lens. ..."A6 Lemmon" on the other hand was captured for the 1st time using a computer-driven CMOS camera with a guided, tracking telescope resulting in multiple subexposures used for stacking. For the 1st time, the 2-dimensional nature of a comet's motion across the sky became a very important factor to deal with. ...it was VERY challenging, indeed! But with all that said, it's a true joy to have captured this remarkable object, while also learning something new. After more than 13 years of fairly intense focus on this hobby, 'learning' continues to be one of its most important aspects. PROGRESSION OF WAY-POINTS AS LEMMON ENTERED AND TRAVELED THRU OUR SOLAR SYSTEM: - The comet approached Jupiter at a distance of appx 217 M miles on 16 April 2025. - Being hidden in the Sun's glare during June and July, the comet reached solar conjunction (visibly closest to the sun as seen by line-of-sight from Earth) on 2 July 2025. It was spotted again in the morning sky, significantly brighter than predicted on the 12th of August when its coma measured about one arc-minute across and with an apparent magnitude of 13.9. By August 19, when it was 150 M miles from the Sun, its total magnitude (nucleus+coma) was estimated to be appx 11, but the comet did not show an obvious tail. A short stubby tail became visible in telescopic images from 25 August. The future brightness of the comet was unpredictable, but it was NOT subjected to any solar outburst when it exited solar conjunction, which would have made its tail much more prominent, and given it much improved visibility. Predictions were still considering it to be "minor" (as comets go). - In August the comet was located in the constellation of Gemini and on 6-7 September was briefly in Cancer before entering the constellation of Lynx. On September 21 the ion tail became active, exhibiting twirls and knots as it interacted with the solar wind, and it became more active as it approached the Sun. A blob of gas was visible moving away from the head along the ion tail on September 23. By late September it had brightened to 8th to 9th magnitude, being visible with binoculars and small telescopes. On 30 September 2025 the comet had brightened to magnitude 6.6, and photographically the ion tail was about 3 degrees long and there was also a dust tail visible too. At this point, the comet was no longer considered "minor", as it captured the attention of the amateur astrophotography community. - Between 15 September and 12 October 2025, observations from the Teide Observatory located in Tenerife, Spain revealed two large spiral jets emanating from the comet, which likely produced its dust tail as it continued to approach perihelion. - The comet experienced a disconnection event on 2 October 2025 as the solar wind stripped away a section of its tail. - In early October the comet entered Leo Minor and after that Ursa Major. By 10 October 2025 it was circumpolar for northern latitudes above 48°N. On 10 October it had an apparent magnitude of 5.6 and its coma was 10 arcminutes across. Photographically, its ion tail was 12 degrees long on October 12. The comet was first spotted by naked eye on 15 October, with an estimated magnitude of 4.8, while 50mm binoculars revealed a tail 1.6 degrees long. On 16 October it passed less than a degree from the binary star Cor Caroli, and moved toward the southeast at a rate of 4 degrees per day. - Spectra of the central part of the coma of C/2025 A6 (Lemmon) were taken with the Échelle spectrograph FLECHAS at the University Observatory located in Jena, Germany on 13 and 18 October 2025. In the wavelength range between 4500 and 7000 Å several emission features in the spectra of C/2025 A6 were detected, with those of C2, NH2, as well as Na being the most prominent. The equivalent width of the Na D1 and D2 emission lines increased significantly between the two observation dates above, while the comet's heliocentric distance decreased to appx 66 M miles. - C/2025 A6 (Lemmon) approached Earth at its closest on 21 October 2025 at a distance of 55 M miles. For reference comparison, Earth is appx 35 M miles from Mars when the 2 of them reach opposition (their closest point) every other year. The comet was visible in the sunset sky with a solar elongation of 42 degrees. It crossed the celestial equator on 2 November 2025 (...being the same date this image was captured). - On 8 November 2025, the comet achieved perihelion, having closed-in on a distance of appx 49 M miles from the Sun. For reference, the mean distance from the Sun to the orbital path of Mercury is appx 36 M miles.
The A6 Lemmon comet was initially classified as an asteroid with an apparent magnitude of about 21.5 in images obtained when it was appx 418 M miles away. Consequently, precovery images were also found in the library of images captured by the PanSTARRS survey dating from 12 November 2024. However, by 21 February 2025, the object had developed a very definite, condensed coma, thereby separating it from the asteroid classification, and cementing it into the recorded annals of comets. It measured appx 2.2 arc-seconds across, with a short tail appx two arc-seconds long. Lemmon's inbound path was carefully measured, and used to calculate its orbital period. Those calculations indicate it will not return for appx 1,350 years. At that periodic frequency, and extrapolating back thru time, its previous perihelion (closest approach to our Sun) would have occurred in the second half of the 7th century, ...during the time of Pythagoras. It will not return again until the year 3175. Composed of ice, dust and rock, its mane appears with a greenish cyan hue due to the presence of diatomic carbon (C2) and cyanogen (CN). Those compounds glow with the characteristic green-cyan color of most comets as they react with radiation and the solar wind emanating from our Sun. The comet made its closest approach to Earth on 21 October 2025 at a distance of appx 55 M miles before achieving perihelion with the Sun. On 3 November 2025 (the day after this image was captured), scientists recorded an apparent magnitude of appx 4.3, and that it was visible to the naked eye and in binoculars in the constellation of Ophiuchus near the globular cluster Messier 12 (M12). When first discovered the comet was expected to only brighten to apparent magnitude 10, resulting in Lemmon's classification as little more than a "minor" comet. Consequently, it didn't do much to capture the attention of the amateur astrophotography (AP) community. But in late October it lit-up brightly, became readily visible and developed a very beautiful, elongated ion tail. It ultimately brightened to an actual apparent magnitude 3.5, which made it about 400 times brighter than originally predicted. That's when the AP community "woke-up". ...literally hundreds of extremely remarkable and beautiful images started pouring-in thru online forums; and the name "Lemmon" quickly became a mainstay. IMAGER'S COMMENTS:Due to a definite lack of forethought, your Host almost missed it. The techniques required to capture a respectable image of a comet are very unique and complex, and therefore challenging. Considerable forethought, planning and preparation are required. Other comets have been captured and included in this collection: 2020 F3 "Neowise" 2021 A1 "Leonard" 2022 E3 (ZTF) "Bolin-Masci" 2023 A3 "Tsuchinshan-ATLAS" But all of these were captured using "single-shot" techniques with a DSLR camera & lens. ..."A6 Lemmon" on the other hand was captured for the 1st time using a computer-driven CMOS camera with a guided, tracking telescope resulting in multiple subexposures used for stacking. For the 1st time, the 2-dimensional nature of a comet's motion across the sky became a very important factor to deal with. ...it was VERY challenging, indeed! But with all that said, it's a true joy to have captured this remarkable object, while also learning something new. After more than 13 years of fairly intense focus on this hobby, 'learning' continues to be one of its most important aspects. PROGRESSION OF WAY-POINTS AS LEMMON ENTERED AND TRAVELED THRU OUR SOLAR SYSTEM: - The comet approached Jupiter at a distance of appx 217 M miles on 16 April 2025. - Being hidden in the Sun's glare during June and July, the comet reached solar conjunction (visibly closest to the sun as seen by line-of-sight from Earth) on 2 July 2025. It was spotted again in the morning sky, significantly brighter than predicted on the 12th of August when its coma measured about one arc-minute across and with an apparent magnitude of 13.9. By August 19, when it was 150 M miles from the Sun, its total magnitude (nucleus+coma) was estimated to be appx 11, but the comet did not show an obvious tail. A short stubby tail became visible in telescopic images from 25 August. The future brightness of the comet was unpredictable, but it was NOT subjected to any solar outburst when it exited solar conjunction, which would have made its tail much more prominent, and given it much improved visibility. Predictions were still considering it to be "minor" (as comets go). - In August the comet was located in the constellation of Gemini and on 6-7 September was briefly in Cancer before entering the constellation of Lynx. On September 21 the ion tail became active, exhibiting twirls and knots as it interacted with the solar wind, and it became more active as it approached the Sun. A blob of gas was visible moving away from the head along the ion tail on September 23. By late September it had brightened to 8th to 9th magnitude, being visible with binoculars and small telescopes. On 30 September 2025 the comet had brightened to magnitude 6.6, and photographically the ion tail was about 3 degrees long and there was also a dust tail visible too. At this point, the comet was no longer considered "minor", as it captured the attention of the amateur astrophotography community. - Between 15 September and 12 October 2025, observations from the Teide Observatory located in Tenerife, Spain revealed two large spiral jets emanating from the comet, which likely produced its dust tail as it continued to approach perihelion. - The comet experienced a disconnection event on 2 October 2025 as the solar wind stripped away a section of its tail. - In early October the comet entered Leo Minor and after that Ursa Major. By 10 October 2025 it was circumpolar for northern latitudes above 48°N. On 10 October it had an apparent magnitude of 5.6 and its coma was 10 arcminutes across. Photographically, its ion tail was 12 degrees long on October 12. The comet was first spotted by naked eye on 15 October, with an estimated magnitude of 4.8, while 50mm binoculars revealed a tail 1.6 degrees long. On 16 October it passed less than a degree from the binary star Cor Caroli, and moved toward the southeast at a rate of 4 degrees per day. - Spectra of the central part of the coma of C/2025 A6 (Lemmon) were taken with the Échelle spectrograph FLECHAS at the University Observatory located in Jena, Germany on 13 and 18 October 2025. In the wavelength range between 4500 and 7000 Å several emission features in the spectra of C/2025 A6 were detected, with those of C2, NH2, as well as Na being the most prominent. The equivalent width of the Na D1 and D2 emission lines increased significantly between the two observation dates above, while the comet's heliocentric distance decreased to appx 66 M miles. - C/2025 A6 (Lemmon) approached Earth at its closest on 21 October 2025 at a distance of 55 M miles. For reference comparison, Earth is appx 35 M miles from Mars when the 2 of them reach opposition (their closest point) every other year. The comet was visible in the sunset sky with a solar elongation of 42 degrees. It crossed the celestial equator on 2 November 2025 (...being the same date this image was captured). - On 8 November 2025, the comet achieved perihelion, having closed-in on a distance of appx 49 M miles from the Sun. For reference, the mean distance from the Sun to the orbital path of Mercury is appx 36 M miles.