Nick, Peter, and friends,

    In my condition of "bright outlier", I kindly disagree when you say "It probably won't get much brighter through March and April".

    COBS recent visual estimates around m1~10.0 are associated to a observed coma diameter in the 2' - 3' range.

    From dark mountain skies the comet shows a wider diffuse outer coma. In my recent observation :

C/2020 R4 (ATLAS):
2021 Mar. 13.21 UT: m1=8.4, Dia.=6', DC=3, 20 cm SCT (77x).
[ Altitude: 12 deg. Mountain location, very clear sky.
Sidgwick method. Tycho-2 comparison stars. SQM: 21.0.].
( Alto del Castro, Leon, Spain, alt. 1720 m; SQM 21.5 at zenith ).

This estimate is in good agreement with the formula :

m1 =  7.5 + 5 log delta + 10.0 log r

providing m1~7.0 at Earth's close approach ( delta = 0.46 AU on 2021 Apr. 23 ), located high in the sky on the Hercules–Corona Borealis border.

    It will be an interesting photometric evolution to follow ... weather permitting.

Best regards and clear skies,

J. J. Gonzalez Suarez

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> On 18 March 2021 Nick James <ndj@nickdjames.com> wrote :
>
>
> Peter,
>
> Thanks for the image obtained under difficult circumstances.
>
> Martin Mobberley got 10.7 on March 9.78 and visual estimates on COBS are
> all around 10.0 now with one bright outlier. It probably won't get much
> brighter through March and April. At least it will become easier for us
> to observe from the UK over the next few weeks.
>
> Nick.
>
> -----------------------------------------------------------------------------------
> On 17/03/2021 17:46, Peter Carson wrote:
> > Hi All,
> >
> > I managed to grab a rather blurry image of C/2020R4 ATLAS from my remote
> > observatory at Fregenal de la Sierra, Spain this morning. It was only 14 degrees
> > altitude, just above the observatory walls and minutes before the start of
> > astronomical twilight.
> >
> > Comphot gives it a visual equivalent mag of 10.07 in a 141 arcsec rad aperture.
> > It’s also showing a short vague dust tail. See my image here
> > http://www.astromania.co.uk/2020R4_20210317_0456_PCarson.jpg
> >
> > It’s blossomed since one of my earlier images in October last year when it was
> > only mag 18. See http://www .astromania.co.uk/2020R4_20201014_2137_PCarson.jpg
> > <http://www.astromania.co.uk/2020R4_20201014_2137_PCarson.jpg>
> >
> >   From southern England it’s currently rising about 03.15UT and at an altitude of
> > around 7 degrees by the start of astronomical twilight and improving in altitude
> > rapidly.
> >
> > Peter
> >
> > Peter Carson Z10
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