Can anyone shed some light on a statement in Astronomy Now about our
interstellar visitor, 3IATLAS, please.

In the October edition there is a one page piece (p10) on 3I/ATLAS.  The
credit from NASA/Caltech to the SPHEREx image of the comet states that
the gas cloud around it extends out to around 350,000km.  This seems to
me to be an enormous distance; is it a misprint? This is which is really
a statement of the size of the comet? In comparison, the diameter of the
Earth is about 12,800km.  Can you throw any light on this statement; it
can't be true surely?

Nick, I enjoyed your talk at Kelling Heath last month, many thanks.

Regards
David Reynolds

On 31/10/2025 18:38, Nick James wrote:
> With all the current excitement about C/2025 A6 (Lemmon) we shouldn't
> forget the much brighter comet that we had this time last year. C/2023
> A3 was a really impressive naked-eye object in mid-October 2024 but it
> has now faded to around 18th magnitude although it is still available
> in the evening sky.
>
> In response to a query from Jonathan Shanklin I have updated the 9
> arcsec lightcurve. The lightcurve of this comet is very unusual. The
> blue curve shows a simple fit to the data points from 2024 July 1
> onwards. It is a passable, although not very good, fit. The period up
> to 2024 April has a rather poor fit to a different curve. The peak
> around 2024 April 15 is supposed to be mainly due to the phase angle
> effect on the very dusty tail which, at that time, was projected
> behind the comet, but that doesn't really explain why the comet was a
> lot brighter throughout the period up to 2024 April.
>
> Jonathan specifically requests if there are any images that can
> provide data in 2025 January. The comet was at a small elongation then
> and was moving from the evening to the morning but if you do have any
> images which you haven't measured and submitted then please contact me.
>
> It is worth keeping this comet under observation and submitting your
> photometry results. The recent large scatter in data is probably due
> to the very crowded field and the high probability that faint stars
> are in the 9 arcsec radius aperture.
>
> Nick.
> To unsubscribe from this list please go to
> https://lists.simplelists.com/subs/