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Pic from last night ~00:00ish on 9/7/25. 2 hours with a baader 610 R+IR filter to combat moonlight, and daylight!
Looks much the same.
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And still much the same last night (9th-10th).
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How do you stack frames at the comet’s offset rate? I have taken exposures of what should be the correct field with my C14 @f/7, and I’ve stacked them normally for an hour’s worth of 1 minute subs, but I can’t identify anything.
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Astroart allows you to input its speed of motion and position angle of the target to provide offsets…
I imagine others use Astrometrica.
Does Astroart still exist?
The website https://www.msb-astroart.com is unresponsive.
According to the Astroart forum the main site is down for maintenance.
However the mirror site at https://www.msbsoftware.it/astroart/ seems to be working normally.I contacted Fabio at AstroArt…
“Thank you for your email. I discovered it last night, the hosting provider has problems. I hope they will fix it ASAP.
If you need to download something, the mirror web site is available at: https://www.msbsoftware.it/astroart/ ”So back on line soon one assumes.
Astrometrica will work for stacking but you will need to enter the offsets manually since the internal ephemeris generator doesn’t work for significantly hyperbolic orbits. I’m hoping Herbert Raab will get that fixed sometime.
It has been interesting to see how many common programs can’t cope with e=6. This will be a good opportunity to get them fixed! I use my own code for stacking and it uses the Laguerre algorithm for solving Kepler’s equation to find the eccentric anomaly as documented by Bruce Conway in 1986 here:
https://adsabs.harvard.edu/full/1986CeMec..39..199C
It is very fast and appears to be stable at least up to the eccentricity of 3I/ATLAS.
I use ASTAP. free and will stack on the ephemeris of any object in the field. Here’s 0T 12/7/25.
2 hours,baader 610 filter.
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So, if you give ASTAP an ephemeris created by (say) JPL Horizons it align multiple images to keep the comet images stacked? Sounds nice.
I see it runs under Windows and Linux – under Linux it could use Astrometry.net for platesolving. How is it doing it under Windows – using the comet’s predicted RA/Dec as the centre to search for star patterns? Plus possibly a hint at sensor pixels size and system focal length?
How do you find it to use?
No such complications. You just select from the drop down – ASTAP has already determined which objects are in the field of view. It uses the standard Allcometels.txt file (which it downloads every now and again, like Cartes du Ciel etc) to figure out where everything is.
It is first and foremost a plate solver, and its lightning fast. It does everything. Han the developer is really cool and adds features if you ask nicely, sometimes next day!
Its easy to use. You’ll love it.
https://www.hnsky.org/astap.htm
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I’ve been doing some astrometry on 3I/ATLAS and have been surprised how much scatter in the magnitude that I’m getting day to day. The plot of magnitudes from MPC astrometry data also shows a huge scatter. This data doesn’t have a consistent photometry aperture or filtering but, for most observers at the moment 3I/ATLAS is a point source so it is surprising. The scatter may be due to measurement errors in the crowded star field but it is worth making estimates of the magnitude if you can.
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I could potentially estimate an R magnitude from my 610 longpass data? Its not ideal but probably close-ish. Would this be useful? Not sure how I’d get magnitudes for the comparison field stars….
Are we thinking this might be an extremely elongated object?!!!
<p class=”wp-dark-mode-bg-image”>I’ve been doing some astrometry on 3I/ATLAS and have been surprised how much scatter in the magnitude that I’m getting day to day. The plot of magnitudes from MPC astrometry data also shows a huge scatter. This data doesn’t have a consistent photometry aperture or filtering but, for most observers at the moment 3I/ATLAS is a point source so it is surprising. The scatter may be due to measurement errors in the crowded star field but it is worth making estimates of the magnitude if you can.
Might the scatter arise in large part from the multitudinous fainter field stars which are too faint to show up clearly in the images but the photons from which will create a very noisy sky background. The noise will add both to the counts at a given a pixel and will vary strongly from pixel to pixel.
Have you tried PSF-fitting photometry, using DAOPHOT for example? It would be interesting to see whether you get significantly different results. DAOPHOT is famous for working well in crowded fields. It is a shame that using it is often a fiddly pita in practice.
Nick – It is definitely worth trying to get some photometry if you can. You could use Sloan r’ mags for your long-pass data and you would at least be able to see if you are consistent from night to night.
Paul – I’m pretty sure that the scatter is due to faint stars in the aperture since this is a very crowded field. I think it is far to early to say anything about the lightcurve of this object but the more observations the better. I have used DAOPHOT and it can be very good but I’ve not been able to get it to work reliably with moving objects.
Paul – I’m pretty sure that the scatter is due to faint stars in the aperture since this is a very crowded field. I think it is far to early to say anything about the lightcurve of this object but the more observations the better. I have used DAOPHOT and it can be very good but I’ve not been able to get it to work reliably with moving objects.
Just a thought: have you tried using DAOPHOT on each sub to remove the stars and then stack the remaining sky background? All that should be left are the very faint objects.
Not suggesting it will give results which are any better but it may prove an interesting experiment.
That is roughly what I was suggesting.The idea came to me when I remembered the image of Halley’s comet which was released shortly before the comet reached aphelion. The stars were subtracted and what remained stacked on the motion of the comet. IIRC, C1/Halley was 29th magnitude at the time.
The idea is testable using images of a star field which is easily measurable before removing all but one of the stars. See whether the before and after measurements are comparable. Repeat with different stars removed and with different fields.
It’s a shame I’ve so little spare bandwidth or I would try it myself with some of my planetary satellite images — of Amalthea, say.
Added in edit: Ah, my earlier response to Nick contained that idea with the suggestion that DAOPHOT’s computed background images be stacked and measured. I know it was posted because I subsequently edited it. Hmmm….
Second edit: Callum rescued it from spam purgatory and it now appears above. Thank Callum.
I finally managed to get it!
https://britastro.org/observations/observation.php?id=89413
Cheers
Ian.
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