Telescope Reviews: Re: Gassendi and environs 16 May 2008

Matt,

That sounds like excellent advice, although I personally think the two most important things are giving (1) an accurate time (hopefully in UT to relieve the reader of the burden of making what is to them likely to be an unfamiliar and uncertain conversion from local time) and (2) an approximate observing location. From these two items everything else about the geometry of the observation (such as colongitude and librations) can be computed. Without them it cannot.

For those interested in the appearance of surface details, the Sun's elevation and azimuth as seen from the feature of interest are actually more important than the colongitude. The observing location is not necessary for this computation, but in addition to permitting an accurate computation of the librations, it also provides a very rough reality check on the stated time (would the Sun have been below the horizon? and would the Moon have been at a reasonable elevation in the sky?).

One generally unhelpful thing (frequently encountered on webpages) is giving the time of the observation by stating the "Age of the Moon". There seem to be different conventions for this, and in the absence of any other information it's impossible to know how an "Age" was obtained and what actual clock time it refers to. It's much safer to give the UT (and observing location) and let the interested reader compute from those whatever else they may be interested in.

All this applies, of course, only to those who want to infer something about the lunar topography from their observations. Many of today's very best imagers appear to regard the Moon simply as an interesting photographic target -- no different from a butterfly or a pebble on the beach. For them what is of interest is the equipment that was used and the way the image was processed. The time is totally irrelevant in this context, except possibly to record the date of the accomplishment. Hence a great many LPOD's, and an even larger number of very fine lunar photos posted on the web give no hint as to exactly when they were taken. This is certainly the prerogative of the photographer (or observer), but it seems unfortunate that they are discarding the considerable value that could be added to their work by so simple an act as noting the approximate time on a wristwatch.

-- Jim

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