Photographing the movement of stars.

The night sky photographed from Sunshine Valley near Hope, BC.

I have always enjoyed photos of the night sky.  There is something mystical about the way the stars turn in an arc.  The pattern appears this way because of the rotation of the Earth.  In my photo above the single point is the North Star, also called Polaris.  It appears as a fixed point in space while all other stars appear to rotate around it.  If you hung a ball on a string and made the make-shift globe spin, you could imagine Polaris being somewhere along that length of string.  Placing a camera on the ball pointing upwards would produce a similar photo, with the center of rotation appearing as a fixed point in space.

Unfortunately, it is not possible to take such a shot from anywhere.  It is very difficult to produce a decent image in populated areas because of light pollution.  The further away from cities you are, the more contrast there will be between stars and the surrounding space.  This has to do with a star's relative magnitude (brightness of the star as seen from earth) and how lit up the night sky is from city lights below.  More light pollution means less contrast between the night sky and the stars that inhabit it.  Brighter skies means muddy images without clear separation between star and sky.

The photo was just over 34 minutes long.  I use an electronic cable release that plugs into the camera, but you can also use an infrared remote actuator if your camera is built to take one.  I used a 20 mm lens on a full frame camera to get a wide perspective on the night sky.  The aperture was set to f/8.  The black section are the surrounding mountains made smaller because of the wide angle lens being used.  The orange, red, white, and blue lights are from cars and trucks passing along the highway which was just at the edge of the viewfinder.  If you look carefully you can see interruptions along the white and blue streaks; those are hedges popping up between the highway and camera.

The easiest way to do this is to go to some remote location and try it yourself.  Camping is one of the best ways to accomplish this as you can set everything up, start the exposure, then disappear into comfort until the exposure is over.  Having trees overhead reduces exposed sky, and longer focal lengths narrows the field of view.  I also discovered that getting a proper focus is hard because the camera has nothing to lock onto.  I used manual focus; do not assume that setting the lens to infinity will work because it may go past that value.  The result, if using minimum aperture, will be out of focus images.  Take a shot and then press play and zoom in to make sure the stars are, in fact, in perfect focus.  Otherwise, you will have spent your night getting blurry photos of the stars.  I learned that the hard way.  It is one of the reasons I used an f/8 aperture instead of a lower setting; the extra depth of field would ensure a correct focus.

Thanks for reading.   www.ericspix.com   Eric Svendsen