Even in a light breeze on a cold and frost night earlier this week, the wind turbines overlooking Galway Bay near Spiddal were swirling. The effect above was created by keeping the shutter open long enough to expose the the stars without blurring them (after 30 secs or so, the Earth's rotation causes stars to register as streaks in an image), and repeatedly firing two flashes at the nearest turbine. Each flash caused the rotors to be illuminated, so the final image shows the position of the rotors over a number of flashes during the exposure (which is also why the stars seem to shine 'through' the rotors).
http://johnsmyth.smugmug.com/gallery/4546543_p3v5U#267870382_MzWcE