To take a night picture, the camera is placed on a stationary surface and the photographer sets a long exposure time (the duration for which the camera's shutter remains open). To give you a point of comparison, daytime pictures are typically taken with an exposure time of less than 1/100th of a second. Night pictures are taken with with an exposure time of 5 full seconds or longer.
In order for long exposure pictures to work, both camera and subject must remain completely still - or else every movement is recorded as a motion blur. Facial expressions are the hardest to keep still and features tends to come out blurry. Bicycles on the other hand, are quite capable of standing motionless and are very patient too - which makes them perfect models for night photography.
Looking at these pictures has made me realise just how comfortable I've become cycling at night. Especially now that it's so hot during the day, that is certainly coming in handy. On Friday and Saturday nights, drivers tend to be more distracted and erratic - so being aware of that (and having one's bike lit up like a Xmas tree) will help you stay safe.