What makes a good observation? Compare the following narratives made by beginners:

1. I went out after observing the late film and observed the new comet. It was a fuzzy blob in my binoculars. Thats my 3rd comet!

2. On January 12 I spent about 20 minutes making casual observations of Messier objects with my 20x80 binoculars then star hopped to find comet NEOS 2010 A1 at 20:20 UT. The coma diameter was about half the distance between Mizar and Alcor and it was markedly brighter in the centre. I couldn't see a tail. I find making magnitude estimates difficult, but it seemed about as bright as 68 UMa out of focus.

The first observer clearly enjoys tracking down comets but the observation is useless. After watching the TV or VDU it will take at least 20 minutes to be dark adapted. The observer doesn't state the aperture and magnification of the binoculars used for the observation and makes no attempt to estimate the magnitude. Most comets are fuzzy blobs. Which comet was observed and when?

The second observer has just about got things right. The date and time of the observation is given, the observer has dark adapted, the size of the binoculars is given. There is a good estimate of the coma diameter and sufficient description to estimate the degree of condensation. Making the magnitude estimate is the hardest part of the observation, but the observer has had a go and stated the method used and the comparison star. The observation although descriptive could easily be coded up into the standard format and used for analysis of the comet's behaviour. Better still the observer could code it up and send it to me electronically!

Full details of how to observe a comet, both for the beginner and advanced observer are given in the Section Guide to Observing Comets, which can be purchased in booklet form from the BAA. A new edition was published in 2002 February and this costs 4 pounds from the BAA Office.

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Published by jds@ast.cam.ac.uk