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 capability 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: Widefield photography involving the north celestial pole invariably leads to very dramatic results and especially when a lengthy time lapse is pursued, thus capturing the rotation of earth around the celestial pole. However, such photos often involve many tens of degrees of sky coverage with little to no attention paid to similar results but using much greater focal length involving two to three degrees arc-coverage. The result below is centered on the north celestial pole itself at 819 mm focal length and involving a field of view which only measures 151 by 101 arc-minutes of sky coverage. Perhaps most surprising is the fact that Polaris, often captured as a white arc around the celestial pole, really involves a red star (B-V = +0.570) and whose real spectral colour finally shows up when using significantly greater image scale. Also of interest are the many stars within the arc described by Polaris around the North Celestial Pole and easily not captured by widefield star trail images as is the case for stars just beyond the same arc.
Please click on the image below to display in higher resolution (1000 x 677)
Proper Star Name:
á Ursae Minoris
2290 +/- 282 x Sun
431 +/- 26 light yrs
RA / Dec:
02h 39m 31s /
+89° 17' 39"
B-V Color Index:
Aug 02-03, 2014
22:37 - 03:37 UT+3
Canon EOS 6D
Baader BCF2 Filter
AP 130/f6.3 Gran Tourismo
294 min (294 x 60 sec) (RGB)
007 min (007 x 60 sec) (Dark)
JPG Fine Image Format
5472x3648 Image Size
Continuous Servo Mode
Dark Frame Reduction
Layers and Lighten