Saturn in the Beehive Cluster
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Fig. 1:  Saturn in the Beehive Cluster imaged 02h 30m January 30 2006. A 15 sec. exposure, 160mm f/1.8, ISO 400. Click the image for an enlargement.

A complete blanket of cloud over Orkney prevented observations of the occultation of BY Cancri on the evening and night of January 25. However, a fine night on the 29/30 gave excellent seeing in the early hours.

The photograph taken at 02h 30m on the 30th (Fig 1) shows Saturn a little below the main body of the cluster. The image close to the left of Saturn is the satellite Titan (mag. 8.3). The satellite was close to maximum elongation (3.5 arc minutes). Usually at this scale it would be swamped by the planet's much greater brilliance.

BY Cancri is the brighter of the pair of stars to the left (21 arc minutes) of Saturn.

JV
30/01/06

Points of accuracy

Dia. 1: Looking south at midnight (Kirkwall) on February 1 2006. Saturn at magnitude -0.2, and just past oppostion, is the second brightest object in the sky next to Sirius at this time. Click the image for an enlargement.

I am unable to say exactly when I first got stuck into astronomy. I have recollections from the years of the Second World War as a very young lad being impressed by a clear, starlit night during the blackout. This came in marked contrast to the busy nights of bombing with the glow from fires, the searchlights and the tracers.

Shortly after the war the family moved into rural Essex and there I was able to see the Milky Way from horizon to horizon during the dark nights when the small street lamps went out before midnight. I joined the British Astronomical Association in my early teens and because I had very little money (I earned 2 shillings a week cleaning my uncles shoes) I could not afford anything beyond a cheap opera glass. But I wanted to make some contribution and so I joined the computing section of the BAA and it was not long before my meagre efforts were being published in that organization's annual Handbook.

And so at an early age I learned a respect for scientific accuracy. It therefore concerns me when I encounter so many errors in publications today that should be avoidable. I am sometimes asked why it is that in the same tome contradictions occur on matters of star magnitudes and spectral classifications. (See archives for notes on stellar magnitudes.)

Photometric catalogues exist containing magnitudes for literally thousands of stars. But many stars are variable and not all variability is either regular in terms of brightness or periodicity. However, there is no excuse for denoting the star Sirius, for example, as mag. -0.9 when it is well established that the brightest star in our skies is of mag. -1.46.

Errors sometimes occur when magnitudes are taken from a positional catalogue such as FK4. In some computer software programmes (and elsewhere) the star Castor is given as magnitude 1.9. To the unaided eye Castor appears brighter than this (1.6). The compiler has obviously taken the magnitude of the primary in this close double star whose secondary is magnitude is 2.9. There are many similar examples of such errors.

It should be noted that in the case of double and multiple stars the combined magnitude is not simply the arithmetic sum of the components. Those wishing to pursue this further should consult Nortons Star Atlas which is a mine of information.

Conflicting data for star magnitudes abound in computer software. This is mostly due to the accessing of various databases in which there may be errors. Not only that but there can be contradictions as to the spectral class of a star. Once again one has to be on the look out for variable and doubles which can confuse the issue for the uninitiated.

Where contradictions occur one has to use their own judgment in assessing the bona fides for a particular piece of information. Sometimes the casual observer may verify such things for himself/herself. Clearly, Castor is brighter to the eye than Algieba (Dia 1) notwithstanding the difference in colour between the two stars.

The internet is a free for all and the information therein can be as wide of the mark as the graffiti on an advertising hoarding.

JV
27/01/06