Film cameras make hardly a difference between long exposure and short exposure (after all, you can store a film for years in the dark). Digital cameras have an inherent noise level that makes longer exposures trickier. Many limit their maximum exposure times to the order of a minute. A frequent phenomenon are "hot pixels" that change state without light influence over time. This may well be a temperature-dependent effect: some cameras do "dark frame subtraction" for longer photographs by taking a photograph with closed shutter and the same duration after the main photograph and then subtracting the image, but once a hot pixel becomes saturated, this of course does not work any more.
So for really long exposures, you want film, or take a number of digital photographs and average them in post-processing.