In film, cinematographers will sometimes shoot "day for night." That is, they'll film a scene during daylight hours, even though the action in the scene is supposed to occur at night within the context of the story. With the right lighting, lenses, filters and post-production techniques, sometimes you can get away with it without the audience noticing. (If you're Ed Wood, you're less likely to successfully master the illusion.)
The photo above might seem as though it were shot on a starry Paris night, but in reality I shot it on a sunny afternoon in Las Vegas. (It's the half-scale replica of the Eiffel Tower at the Paris casino.) The "stars" are actually dust grains that were captured when I scanned the film; rather than cleaning them up with Photoshop, I decided I liked the odd day-for-night effect and left them alone.