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Celestial hemisphere:  Northern  ·  Constellation: Virgo (Vir)  ·  Contains:  Solar system body or event
Comet C/2023 A3 (Tsuchinshan-ATLAS): An early image and 3.5 hour animation, Rick Veregin
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Comet C/2023 A3 (Tsuchinshan-ATLAS): An early image and 3.5 hour animation

Comet C/2023 A3 (Tsuchinshan-ATLAS): An early image and 3.5 hour animation, Rick Veregin
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Comet C/2023 A3 (Tsuchinshan-ATLAS): An early image and 3.5 hour animation

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Acquisition details

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Description

The Comet
  • Comet C/2023 A3 (Tsuchinshan-ATLAS) was discovered by the Tsuchinshan Chinese Observatory in January, and independently by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on 22 February 2023. The A3 indicates it was the 3rd comet discovered in the 1st half-month, A (half-month intervals are labelled A,B,C,D…).
  • C/2023A3 is in a retrograde orbit (opposite to the planets) with a parabolic-like path, which means while it took millions of years to arrive from the Oort Cloud,  outbound it may not return.
  • C/2023 A3 is predicted to become  naked eye visible, but it doesn’t really brighten until early August, reaching a maximum of magnitude 2 on Oct 9th at closest approach. However, its altitude becomes quickly unfavorable: by August it sets with the Sun. Still, after closest approach, for a few days in  mid-October it might be possible to see it near maximum brightness, though it is only about 15⁰ degrees altitude as the Sun sets.  It dims dramatically into 2025 as it moves to higher altitudes.
  • Thus, I took my chance now to get it in now, given there is a very small window later. For my imaging the comet was 1.76 AU (or 264 Million km) distance from me, at magnitude 11.3.  it is in the constellation of Virgo, and this area was really very devoid of stars. As darkness fell and I started imaging, it was at 40⁰ altitude, down to 15⁰ degrees by the time I had to stop (no point imaging rooftops), at 2:30 AM. In any event, it was very favorable conditions for a long integration and a reasonable altitude for a good image.

Color
  • In my image the comet had strong green and red signals, but blue was lacking. Green and red give the yellowish green that we see in my image, though the edges of the tail showed red.
  • Dust tails reflect all wavelengths generally, so a dust tail would be nearly white in an image. Dust tails are also gently curved by gravity, which is clearly shown here.
  • Ionic tails are straight pushed out directly opposite the sun.
  • Yellow in comets can come from the sodium doublet.
  • C2 molecules emit mainly in green and a bit in blue—these are known as the Swan bands.Comet Neowise, for example, was mainly C2 and Na emission.
  • Red can be due to NH2 or OI, such as in Comet 42P/Witanan, which also had strong C2 Swan bands.
  • Closer to the Sun we often get two tails, the dust tail, and a blue ion tail due to CO+ ions.
  • At this point, however, I have not found any spectra of C2023A3 to be sure of compositional details.

Capture
  • I initially collected data with my L-Pro filter, but was not at all happy with the star halos, even at 30 second exposures. This was first try with the L-Pro in my Bortle 8, so not sure what the issue was. I did collect 15 minutes of data before the meridian flip.
  • After the flip, the L-Pro stars were still ugly, so I switched to using no filter for the next 3.5 hrs of 60 s subs, which solved the star issues. Correcting for the difference in sub exposure times, both filters gave me the same background counts, background S/N, and similar number of stars.  Thus, I’m not seeing that the L-Pro in any way helps with my light pollution.

Processing

   DSS
  • For both datasets, I used the comet stacking mode, with a kappa-sigma rejection (sigma=2, iterations=5) to median, which worked well, leaving only a few faint broken trails here and there.
  • I also used star stacking for the no filter data, which showed good stars, and the blurred comet.

     Startools
  • There was a bad light pollution gradient, as the comet was sandwiched between a streetlight and the moon, so I had to crop out the edges, and then use the background wipe in Startools to tame it.
  • After the development stretch, I did a multiscale sharpening on the comet, using only the largest two size scales, which was effective to bring up the comet signal.
  • This was followed by color development and a background isolation step.
  • For the stars, I did the background wipe, deconvolution, color, and background isolation.

    Photoshop
  • I used both the L-Pro and no filter comet images, adding them in a ratio, so the S/N contribution from both sets would equal.
  • I used the manual fill to remove any broken star trails in the comet image.
  • I then applied final tweaks to color. Note in the whole process there was no selective area color adjustments, all color adjustments were global.  The comet had very little blue in it, which is why it appears yellow.
  • From the star stack, stars were removed using StarXterminator, then subtraction gave the star layer. I added the galaxy back into the star layer.The stars and galaxy were then added back with linear dodge (add), adding the star signal directly on top of the comet layer.

    Animation (will be a bit slow to load)
  • Note, this is not a “true” animation, which would involve showing the comet image at each minute against the stars in that time frame.
  • The stars here are the result of 3.5 h total integration and comet nearly 4 hours of total integration.
  • What I have done is move the comet image exactly where it appeared against the stars. The comet was moved to create 30 frames at different positions, animated in Photoshop.

Comments

Revisions

  • Final
    Comet C/2023 A3 (Tsuchinshan-ATLAS): An early image and 3.5 hour animation, Rick Veregin
    Original
  • Comet C/2023 A3 (Tsuchinshan-ATLAS): An early image and 3.5 hour animation, Rick Veregin
    B

B

Title: Animation over 3.5 hours

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Comet C/2023 A3 (Tsuchinshan-ATLAS): An early image and 3.5 hour animation, Rick Veregin

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