One of the most basic types of astrophotography and yet equally stunning is that involving star trails, particularly around the celestial
poles or immediately due east or west. In addition to capturing the motion of stars around the north pole which are circumpolar and, hence,
never rise or set, we also have the ability to capture seasonal constellations and stars in such photos, thus allowing for different
opportunities during different seasons. Star trail photos also provide direct evidence that our planet rotates and does so at a rate of 15°
per hour. Furthermore, by studying the arc for a particular star, especially as far away from the pole as possible, one can indirectly
estimate the length of the (total) exposure which often ranges from seven to eight hours in duration and is totally dependent on the end of
astronomical twilight one evening and its onset the following morning.
Many star photos are centered on Polaris, a double star system which represents our quickest means to locating the north celestial pole, for
it lies less than 1.0° from it, and is an excellent starting point for the polar alignment of a telescope (and finding your way home if you
are lost!). Due to the extended length of the typical exposures involved, the best film for such work is Kodak Elite Chrome (ISO 100) whose
reciprocity failure is nearly zero or Fujichrome Velvia and Provia (ISO 50 and 100) emulsions with equally impressive curves! With respect to
equipment, it is rudimentary, for a camera with extended exposure capibility is required along with a firm tripod and shutter release and
locking cable. It is also preferable that the camera used have a mechanical shutter so that battery consumption and power does not become an
issue during mid-exposure. The final requirement is a location with dark skies - the darker the better so that the trails and their
colouration will be as bright and contrasty as possible - with, preferably, an interesting foreground which can be used to enrich the final
result.
Note:
The multi-exposure sequence below was started approximately 40 minutes after the setting of the 10-day old moon and during the projected peak
of the annual Perseid meteor shower. As described and illustrated earlier, activity was nominal with only one Perseid captured in the photo
below (click here).
Proper Star Name: Polaris Bayer Letter: á Ursae Minoris Tycho Catalog: TYC 4628-237-1 SAO Catalog: SAO 308 Luminosity 2290 +/- 282 x Sun Distance: 431 +/- 26 light yrs RA / Dec: 02h 35m 39s / +89° 16' 21" B-V Color Index: +0.570 mag Magnitude: 1.98 |
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Date: Aug 12, 2008 02:42 - 05:22 UT+3 Location: Mount Kithaironas Attiki, Greece (38.1831° N, 23.2486° E) Equipment: Canon EOS 300d Canon EOS EF-S 18-55 mm  @ 18 mm / f3.5 Exposures: 271 x 30 sec (RGB) 006 x 30 sec (Dark) ISO 800 JPG FINE Image Format 3072x2048 Image Size Servo Mode Software: Digital Camera Pro V2.1.1.4 Photoshop CS2 Processing: Reduction Layers & Lighten Resampling (25%) JPG Compression |