<html><head></head><body><div style="color:#000; background-color:#fff; font-family:Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div id="yui_3_16_0_ym19_1_1525105124398_3359"><span>Hi Jon,</span></div><div id="yui_3_16_0_ym19_1_1525105124398_3364" dir="ltr"><span id="yui_3_16_0_ym19_1_1525105124398_3674">I have made some comet magnitude measurements using Nick's Comphot software and intend to do more. There seemed to be a issue with the magnitudes derived for bright diffuse comets such as 252P Linear which we observed in 2016. The magnitudes for the fainter more compact comets seemed more in line with those reported on COBS by other observers, using a variety of measurement and reduction methods. This autumn/winter I intend to measure and report more photometry to you using Comphot. All night twilight at my latitude 58d N means I have to stop for around 3 months until dark sky returns here. I note that Jakub Cerny has also introduced a comet photometry software (Kopr) which some observers are using. Perhaps Nick will give an update on the current situation with Comphot and if any changes and updates are planned or required. I suspect that what is needed more than anything is some sustained usage of Comphot by many observers to test the reliablity of the results produced using it.</span></div><div dir="ltr" id="yui_3_16_0_ym19_1_1525105124398_3797"><span id="yui_3_16_0_ym19_1_1525105124398_3674">Denis Buczynski </span></div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1525105124398_3688"><br><br></div><div class="yahoo_quoted" id="yui_3_16_0_ym19_1_1525105124398_3505" style="display: block;"> <div style="font-family: Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1525105124398_3504"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, Sans-Serif; font-size: 16px;" id="yui_3_16_0_ym19_1_1525105124398_3503"> <div dir="ltr" id="yui_3_16_0_ym19_1_1525105124398_3502"> <font id="yui_3_16_0_ym19_1_1525105124398_3850" size="2" face="Arial"> <hr id="yui_3_16_0_ym19_1_1525105124398_3878" size="1"> <b><span style="font-weight:bold;">From:</span></b> "Shanklin, Jonathan D." <jdsh@bas.ac.uk><br> <b><span style="font-weight: bold;">To:</span></b> BAA Comets discussion list <comets-disc@britastro.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Monday, 30 April 2018, 17:00<br> <b><span style="font-weight: bold;">Subject:</span></b> [BAA Comets] Comet magnitudes<br> </font> </div> <div class="y_msg_container" id="yui_3_16_0_ym19_1_1525105124398_3509"><br><div id="yiv0453218687">
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<div class="yiv0453218687MsoNormal" id="yui_3_16_0_ym19_1_1525105124398_4952">Dear all,</div>
<div class="yiv0453218687MsoNormal" id="yui_3_16_0_ym19_1_1525105124398_3799"> </div>
<div class="yiv0453218687MsoNormal" id="yui_3_16_0_ym19_1_1525105124398_3506">Many of you submit excellent images to the BAA archives, but very few are currently reducing their images to provide visual equivalent magnitudes. With the general decline in visual observing these are worthwhile measurements to make,
particularly for fainter periodic comets, and contribute greatly to the cometary analysis reports that I write for the BAA Journal. “Fainter” these days generally means anything you can’t see in binoculars, though there are a handful of dedicated observers
still making telescopic estimates. We are now getting to the stage where we have data for multiple returns of periodic comets and this allows determination of their long term behaviour. Could I encourage all imagers to try the procedures at
<a rel="nofollow" target="_blank" href="https://www.britastro.org/node/11124">https://www.britastro.org/node/11124</a> and send their results to me in ICQ format. They will get used, and more promptly than in the past; the paper on the brighter comets of 2015 has just been accepted for
publication, and this includes derived magnitude parameters for fainter comets as well.</div>
<div class="yiv0453218687MsoNormal" id="yui_3_16_0_ym19_1_1525105124398_3510"> </div>
<div class="yiv0453218687MsoNormal"><span style="">Regards,</span></div>
<div class="yiv0453218687MsoNormal"><span style=""> </span></div>
<div class="yiv0453218687MsoNormal"><span style="">Jon Shanklin</span></div>
<div class="yiv0453218687MsoNormal"><span style="">Visual Co-ordinator, BAA Comet Section</span></div>
<div class="yiv0453218687MsoNormal"><span style="">http://www.ast.cam.ac.uk/~jds/</span></div>
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