My idea was to take pictures systematically with a semi-wide angle 35mm f2.8 lens using a standard 3minute exposure onto fast slide film - 3M Scotch 1000 was used throughout the project. Each picture covers an area of about 50 x 35 degrees. The orthogonal orientation of the centre of each frame to lines of RA and Declination and the careful positioning of adjacent frames to minimise overlap (which becomes increasingly larger at high Declinations) has enabled me to photograph the whole of the northern sky, down to approximately Declination -15degrees, on less than the equivalent of one roll of film.
In practice, many rolls of film have been taken over the years. It has proved difficult to get consistent results. Poor weather, the effects of seeing conditions, sky transparency, increasing light pollution - minimised by using a didymium filter to cut out low-pressure sodium glow from streetlights - and batch to batch variation in film and processing, have all influenced the project. The pictures were taken in the UK from dark sky sites in either Wales or the Peak District National Park. Lupus and Scorpius were taken from Baja California in July 1991 to extend coverage of the summer Milky Way as far south as possible.
The relatively small aperture of a 35mm focal length f2.8 lens has limited the faintest star shown to about 8th magnitude. This is rather fainter than can be seen with the naked eye even under very dark skies. The advantage is that the pictures are not overcrowded with stars and the constellations are easily identified. The result, I hope, is a realistic picture of the night sky that can be used in conjunction with a good star atlas, such as Norton's or the more modern Wil Tirion's Cambridge Star Atlas 2000.0 to allow the easy identification of constellations, stars and deep sky objects. Computer image-processing has assisted the project by enabling star identification and constellation lines to be added to the original slides. To minimise the effect of overcrowding, only those stars that form the essential outline of constellations are identified with Greek letters, placed to their left if possible. Deep-sky objects are identified if they are visible on the pictures, with their NGC or Messier numbers placed to their right or slightly below the object. Constellation outlines are those that by popular consensus and use on other maps are the most readily identifiable.
All images © Copyright K.J. Kilburn
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