As the others have already mentioned, these are "dead pixels." When taking exposures longer than 20-30 seconds, these defective pixels become more and more prominent. There is an easy way to get rid of these dead pixels - unfortunately it may require the "shoot it again filter." The idea is to take your main exposure, then immediately take a second "dark frame" of the same exposure time and ISO, with the lens cap on. This works because, generally speaking, those dead pixels are always in the same spot; however their characteristics can change due to exposure settings and sensor temperature. Once you have that data, the two files can be loaded into Photoshop as a stack. You'll then have two options: Set the "dark frame" to "Subtract" blend mode. Select black of dark frame using Color Range, invert Selection, Content Aware Fill the main image. The catch to the first method is all the subtracted areas will be black, so depending on the image this may not yield satisfactory results. Here are embellished examples: There is a possibility that simply taking another image at this point (with the exact settings as the problem image) may suffice. Worth a try.
... View more