Monthly Archives: December 2025

Sh2-86 A Lighthouse at Sunset with an Oncoming Storm or, more simply, the Lighthouse Nebula

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Sharpless Sh2-86 does not have a common name, and I think it’s fun to come up with my own names for these objects.  To me, with this framing, the “finger” or “pillar” in the lower center looks like a lighthouse – can you see the beam pointing to the left?  It’s standing on a rocky shore near the blue water (can you see a fish jumping out of water to its right?).  It’s at sunset – the vibrant red to the right – with a storm coming in – the dark spots to the left.  So I call this image “A Lighthouse at Sunset with an Oncoming Storm.” Or, more simply, the Lighthouse Nebula.

This image shows HII region Sharpless Sh2-86 (the whole image), the open cluster NGC6823 (stars in the center of the blue region), and emission nebula NGC6820 (pink spot to the upper left). 

Sh2-86 is an HII region emission nebula, a region of ionized atomic hydrogen.  It is a peak region in a molecular cloud, an interstellar cloud of gas molecules, whose density allows the formation of molecules such as molecular hydrogen (H2) and carbon monoxide (CO).  It is located in the “local spur” region between the “local arm” of the Milky Way where our solar system is located and the “Sagittarius Arm” which is closer to the galactic center.  (There’s a great overhead diagram of our galaxy showing the different arms in A Parallax-Based Distance Estimator for Spiral Arm Sources.)  One theory is that the region is made of three different molecular filaments moving at different velocities, the intersection of which led to the formation of the young open cluster NGC2823.

The young open cluster NGC6823 is about 3 million +/- 1 million years old.  It contains at least 17 OB type stars, short-lived, hot, massive stars that emit UV radiation that ionizes the surrounding molecular cloud.   

Sh2-86 also contains emission nebula NGC6820 which contains an embedded cluster of stars.  

Sh2-86 is located in the Milky Way, approximately 6500 light years away.  This image is 42.2 arc minutes across, so the image is approximately 80 light years across. 

In this image, the stars came from images using red-green-blue filters with a little over 30 minutes of data each, and the nebula came from images using Sulfer ii (4.35 hours of data mapped to red), Hydrogen alpha (3.05 hours of data mapped to green) and Oxygen iii (15.6 hours of data mapped to blue) filters, the standard SHO mapping.  But after doing that mapping, I used Narrowband Normalization to shift the colors so that it wasn’t overly green and to enhance the reds and blues.  The nebula was processed separately from the stars to maximally enhance it.  After making this uber-vibrant version, I tried several rounds of trying to make a more subdued version, but I just didn’t like them as well.  So the vibrant color was an artistic decision.

What do you think of the colors?  What do you think of the name?

Camera geek info – Narrowband:

  • William Optics Pleiades 111 telescope
  • ZWO 2” Electronic Filter Wheel
  • Antila SHO and RGB filters
  • Blue Fireball 360° Camera Angle Adjuster/Rotator
  • ZWO ASI183MM-Pro-Mono camera
  • William Optics Uniguide 32MM F/3.75
  • ZWO ASI220MM-mini
  • ZWO ASiair Plus
  • iOptron CEM40
  • Friendswood, Texas Bortle 7-8 suburban skies

Frames:

  • August 7, 2025
    • 61 180 second Gain 150 Ha lights
    • 30 0.5 second Gain 150 Ha flats
  • August 8, 2025
    • 86 180 second Gain 150 Oiii lights
    • 30 0.2 second Gain 150 Oiii flats
  • August 9, 2025
    • 45 180 second Gain 150 Oiii lights
    • 30 0.2 second Gain 150 Oiii flats
  • August 14, 2025
    • 77 180 second Gain 150 Oiii lights
    • 30 0.2 second Gain 150 Oiii flats
  • August 16, 2025
    • 86 180 second Gain 150 Oiii lights
    • 30 0.2 second Gain 150 Oiii flats
  • August 24, 2025
    • 7 180 second Gain 150 Oiii lights
    • 30 0.2 second Gain 150 Oiii flats
    • 100 20 second Gain 150 Red lights
    • 30 0.02 second Gain 150 Red flats
    • 99 20 second Gain 150 Green lights
    • 30 0.01 second Gain 150 Green flats
    • 96 20 second Gain 150 Blue lights
    • 30 0.01 second Gain 150 Blue flats
  • September 4, 2025
    • 69 180 second Gain 150 Sii lights
    • 30 0.5 second Gain 150 Sii flats
  • November 25, 2025
    • 8 180 second Gain 150 Sii lights
    • 30 0.5 second Gain 150 Sii flats
    • 1 180 second Gain 150 Oiii lights
    • 30 0.2 second Gain 150 Oiii flats
  • November 26, 2025
    • 10 180 second Gain 150 Sii lights
    • 30 0.5 second Gain 150 Sii flats
    • 10 180 second Gain 150 Oiii lights
    • 30 0.2 second Gain 150 Oiii flats
  • 30 Flat Darks matching flat durations from library
  • 30 Darks matching light durations from library

Processing geek info:

  • PixInsight
  • BlurXterminator
  • NoiseXterminator
  • StarXTerminator
  • Narrowband Normalization

Comet 3I ATLAS on 11 November 2025 – An Interstellar Visitor

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We recently took a trip to enjoy the glorious dark skies in Dell City, Texas.  Imaging Comet Lemmon was on the agenda, but I was delighted when I realized that I could also capture Comet 3I ATLAS, an interstellar visitor to our solar system, with my small telescope!

Comet 3I ATLAS (C/2025 N1 ATLAS) is an interstellar comet.  The designation “3I” means it’s the third interstellar comet to be discovered in our solar system.  The designation C/2025 N1 can be interpreted as follows: “C”: it is a non-periodic comet (comet with an orbital period > 200 years), “2025”: it was discovered in 2025, “N1”: it was the first comet (1) discovered in (N) the thirteenth half-month of the year (the first half of July) (the letter I is skipped due to its visual similarity to the number 1).  The name ATLAS indicates it was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) station.  

Comet 3I ATLAS is considered a comet because it is releasing gas and has formed a visible coma of gas around its nucleus, as you can see in the picture.

Comet 3I ATLAS is the third known interstellar object (object not gravitationally bound to any star) to pass through our solar system, but that’s more likely to be due to improving detection capabilities and not due to the lack of earlier visitors.  We know it’s an interstellar object because of its high velocity and hyperbolic trajectory.  Its trajectory is shown as the purple line in the picture above (image courtesy of TheSkyLive.com TheSkyLive).  As you can see, it did not cross Earth’s orbit (the blue circle).  

One feature of comets is that they are visibly fuzzy, as you can see in the picture and video.  Another is that they are moving relative to the stars, as you can see in the video.    

As 3I ATLAS passes through our solar system, scientists are collecting more data on it and determining more about it.  An early paper from July suggested it might have come from our galaxy’s “thick disk” – the population of older stars above and below the “thin disk” where our solar system is – and so might potentially be over 7.6 billion years old, older than our solar system (there’s a cool image of the orbits of the comet and our sun relative to our galaxy in the news release).  A paper from August suggests it came from our galaxy’s “thin disk” and another paper from August suggests it is 3 – 11 billion years old.  

I think it’s really cool to see science being done in real time, and I look forward to seeing everything that scientists can figure out about this neat object!

Camera geek info:

  • William Optics Zenith Star 73 III APO telescope
  • William Optics Flat 73A
  • ZWO 2” Electronic Filter Wheel
  • Antila RGB filters
  • ZWO ASI183MM-Pro-Mono camera
  • William Optics Uniguide 32MM F/3.75
  • ZWO ASI220MM-mini
  • ZWO ASiair Plus
  • iOptron CEM40
  • Dell City, Texas Bortle 2 – 3 skies

Frames:

  • November 11, 2025
    • 15 60 second Gain 150 R lights 
    • 30 0.05 second Gain 150 R flats
    • 16 60 second Gain 150 G lights 
    • 30 0.02 second Gain 150 G flats
    • 16 60 second Gain 150 B lights 
    • 30 0.02 second Gain 150 B flats
    • Matching darks and flat darks from library