Comet Lemmon: it keeps getting better

 I just returned from three nights in the big city (Santa Fe), during which there was no comet viewing.  The sky tonight (25 Oct) was mostly clear at dusk.  The crescent moon was partially obscured by thin clouds as it sank behind the Bristol Head ridgeline.

Comet C/2025 A6 (Lemmon) is now brighter than magnitude 4.  I was able to see it without optical aid as it hung low over Bristol Head at the end of Astronomical Twilight.  With a camera, the view is magnificent.  The blue ion tail currently spans more than 7°, and it is twisted and broken by the solar wind.

Sony A7iii + Nikon 180mm f/2.8 ED Ai-s.

 

Olympus E-M5iii + Rokinon 135mm f/2.

Comet C/2025 R2 (SWAN) is still there, but fading, in the southern sky.  At magnitude 6.6, it is not visible without binoculars or a telescope.

Comet SWAN.  Olympus E-M5iii + Rokinon 135mm.

 

Watching the comet

 Last night I actually watched the comet with a telescope rather than relentlessly photograph it.  I used a 4.25-inch (108 mm) f/3.7 reflector whose mirror I ground and polished as a teenager over 55 years ago.  With a 24 mm eyepiece in the drawtube the magnification was about 17x.  

One takeaway from the visual observing was just how many satellites were continually zooming through the field of view.  We are rapidly losing an unimpeded view of the night sky.

Of course, I also had a camera set up.  I used a Sony A7iii camera and a Nikon 180mm f/2.8 ED Ai-s lens.

Comet C/2025 A6 (Lemmon), 21 Oct.

 

Photobombed by satellites!

The orbital velocity of a comet can be quite high as it nears the sun.  The following animation shows that the motion against background stars is evident over a period of only 20 minutes.

20-min time span.

 

Comets Lemmon and SWAN, Monday evening

 I dragged myself outside this morning to get pictures of Comet C/2025 A6 (Lemmon) around 6 am MDT.  One of those pictures is in the previous post.  That is likely the last time, because as the comet gets closer to the sun the sky is getting too bright by the time it rises above the distant ridgeline.  In the evening, the comet is still easily visible above Bristol Head as darkness falls and is very near its expected peak brightness of magnitude 4.  That is naked-eye brightness, but it is much better observed with binoculars.

For a change of pace, this evening I used a Sony A7iii camera with a Nikon 180mm f/2.8 ED Ai-s lens.

Comet C/2025 A6 (Lemmon) over Bristol Head. 7:50 pm MDT 20 Oct.

 

Comet Lemmon. 8:00 pm MDT 20 Oct.

Comet C/2025 R2 (SWAN). 8:05 pm MDT 20 Oct

The name "Lemmon" derives from the Mount Lemmon Observatory in the Santa Catalina Mountains.  The name "SWAN" derives from the Solar Wind Anisotropies (SWAN) instrument on the ESA Solar and Heliospheric Observatory (SOHO) spacecraft.

Comets in the morning, comets in the evening

 At any given time, it is normal for there to be a dozen or more comets within photographic range.  More rarely, one or more of these comets will be bright enough to be seen with the unaided eye or with small optical instruments such as binoculars.  There are currently two "bright" comets: C/2025 A5 (Lemmon), near magnitude 4, and C/2025 R2 (SWAN), near magnitude 6.  Comet Lemmon has been visible in the both the morning and evening sky.  Comet SWAN is an evening-only object.

The following images were obtained over the past three days with an Olympus 75mm f/1.8 lens and a Rokinon 135mm f/2 lens. 

Morning Comet Lemmon rising over Snowshoe Mt.  6:05 am MDT, 20 Oct.

 

Morning Comet Lemmon, 5:48 am MDT, 18 Oct.

The wispy tail extends about 3°.  5:48 am 18 Oct.

Morning Comet Lemmon, 5:41 am 18 Oct.

Evening Comet Lemmon over Bristol Head.  7:45 pm 18 Oct.

Comet C/2025 R2 (SWAN) is the green blob in the upper-left corner. 18 Oct.

Comet SWAN is currently traversing across the Milky Way.  The nebulae M16 and M17 are on the right-hand side of the above image.  The green glow of the comet is from the emission of diatomic carbon (C₂).

A closer look at Comet SWAN on 19 Oct.

One of the fainter comets is C/2024 E1 (Wierzchos), near magnitude 13.  It is just recognizable as a faint blob at the center of this 60 sec exposure:

Comet C/2024 E1 (Wierzchos), 19 Oct.

 

Evening Comet Lemmon, 7:40 pm MDT, 19 Oct.

Comet C/2025 A6 (Lemmon) setting over Bristol Head

At my location the mountains to the west rise up to about 12°  above the horizon.  There was a fairly narrow time window, about 20 minutes, between the end of Nautical Twilight and when the comet set behind the Bristol-Head mountain ridge.

Comet C/2025 A6 (Lemmon) above Bristol Head.  Olympus 75mm f/1.8, ISO 800, 30 s.

 

Rokinon 135mm f/2, ISO 1600, 60 s.

Photo-bombed by satellites!  Not much time for a do-over, the comet is about to slip behind the ridgeline:

Rokinon 135mm f/2, ISO 1600, 30 s.

 The comet's tail seems to extend about 2° in these short exposures.

Comet C/2025 A6 (Lemmon) near dawn

 At 5:15 am the waning crescent moon was rising over Snowshoe Mountain and Comet Lemmon (C/2025 A6) was low in the northeastern sky.  When I set up the cameras it was still too dark to see that the northern view was obstructed by power lines.  I am sure that there is some fancy post-processing that can remove the power-line shadows, but next time I will just scout out a better location ahead of time.

The comet is currently at about magnitude 4.5, which makes it a naked-eye object.  However, it is tough to see through the low-elevation airglow murk.  It was easy to pick up with binoculars. 

Olympus 75mm f/1.8.  ISO 1600, 30 s.

 

Rokinon 135mm f/2.  ISO 1600, 40 s.

There are two galaxies visible in this image to the upper-right  and right of the comet: NGC 5005 and NGC 5033, respectively.

Star trails over Bristol Head

 The waning Harvest Moon lit up the landscape for this two-hour exposure.  A lot of airplane trails are visible—hard to avoid during this 9–11 pm time period.  Olympus E-M1iii + Leica 9mm f/1.7.

The next morning: