As we’ve discussed, the heavens are actually moving through the night at a fair old lick, enough to be recorded as motion blur if your exposure length exceeds the ‘500 rule’ (see the previous page), resulting in stars being recorded as elongated streaks, rather than dots. But photography is a creative medium, so what if we were to deliberately allow these streaks to occur, to help convey the stars’ movement in our static image?
This technique is known as star trails, but for meaningful movement to be recorded we really need an exposure time of at least an hour, stretching to several hours for longer, more impressive-looking trails. Such lengthy exposures introduce their own set of problems. The longer the sensor is exposed, the greater the build-up of image noise,…