Hi Miko?aj: SWAN images are a little harder to work with than SOHO LASCO C3 and C2 due to the low cadence (daily), low angular resolution, and high noise. I use this (unfortunately non-secure) site to get the latest images, and/or GIF movie covering roughly the most recent 2 ? weeks:

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I then use ImageJ to open the animated .gif file, and then increase the contrast to improve visibility of comets just above the noise floor. There are currently three moving objects visible in SWAN: ?C/2023 A3 (Tsuchinshan-ATLAS), 333P/LINEAR, and Venus. Venus is easiest to see, moving right-to-left to the left of the sun centered near pixel X=156, Y=291 in the most recent 12/3 image. 333P/LINEAR is moving rapidly upward in the image to the upper right of the sun @ X=336, Y=196 on 12/3. Finally, C/2023 A3 has been dimming rapidly in SWAN, still just visible on 12/3 at X=179, Y=238 to the sun’s upper left.

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For a new discovery, I would wait until I had at least 4 solid images showing consistent motion before I’d get too excited, and for very dim objects I might wait until I had 5 or even 6 before I’d try to confirm it telescopically. To do the latter, you’ll need a way to convert SWAN’s raw pixel coordinates to approximate right ascension and declination. I can provide you simple equations for doing that when you get to that point, and the next step after that is to check if those positions correspond to an already known object. For that quick check, I like to use Seiichi Yoshida’s website:

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If the candidate object’s coordinates don’t match anything bright (12^th magnitude or brighter) on Seiichi’s page, then it’s time to create crude astrometry which can be used to generate a rough orbit and predict the object’s future positions. That’s the hardest part of the problem, but I can walk you through it if you’re interested.? --Rob

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Hi again,

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All very good additional advice from Vladimir – a very experienced SWAN discoverer. He makes a good point about checking the recent SkyCoverage maps: if a candidate object’s sky location has been recently visited by one or more of the major surveys (that routinely detect objects over 500 times dimmer than what SWAN can see), then the SWAN detection is probably spurious. That said, past comets first detected in SWAN tended to have poor solar elongations, and thus were in regions of the sky not regularly scanned by the surveys. For a related reason, you’re more likely to pick up a previously unknown comet in the southern hemisphere vs. the northern hemisphere since most telescopes (and visual comet hunters) are north of the equator.

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As Vladimir also points out, the discovery credit rules are different for SWAN vs. SOHO. For SOHO it often comes down to who can type the fastest after a couple images of a comet have been posted upon entering the C3 or C2 field of view. There is generally no such urgency for SWAN since the image cadence is 240x slower, and a real comet in SWAN is almost always transitioning from being invisible in one image to barely visible in the next. You are also “competing” with a much smaller pool of skilled comet hunters.

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Finally, there is a much greater chance of “seeing” a false comet in SWAN (vs. in SOHO), and I believe the MPC and CBAT both frown heavily on over-reporting of what turn out to be SWAN false positives. (And by over-reporting, I mean a false-to-real ratio greater than unity is NOT recommended!) It is far better to try to confirm the object from the ground before reporting, and today there are a lot more options for doing so than even five years ago.

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Best of luck!? --Rob

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My advice is not to send anything to CBAT that only appears in 3 SWAN images; I would consider 4 images a bare minimum. Personally, I don’t see any moving objects that disappear behind the black solar-occulting region in recent images. If the object you’re considering is near pixel X=186, Y=283, then that is the blue supergiant star mu Sagittarii.? --Rob

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I recommend using the _rfa versions of the images – especially when looking close to the solar occulting area, e.g.

swan_ARecl_sm_20241205_0002_rfa.gif. When you do so, you’ll see more unblocked sky and the exceedance

you’ve identified will no longer look very compelling.? --Rob

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Hi Miki,

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From the main page at (note the UNSECURE web address), go to the left column and click on “Summary images (old)”. Then at upper right, click on “COMET TRACKER’S MAPS”. Each date has two images – the first is the regular .gif, and the second is the _rfa.gif version with less area occulted. Note that the GIF movies that they create are of the _rfa.gif images.? --Rob

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Your browser probably isn’t allowing you to access it because it’s http:// and not https://. I think I had to make an exception for the site so that Firefox would open it.? --Rob

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