This is a panoramic of 7 discrete images. Each image is a result of a four 2 second exposures that are stacked to minimize noise. The trick is to take the pictures (2 second mirror lockup, 2 second exposure, 2 second noise reduction * 4 is about 30 seconds * 7 is about 3.5 minutes) before the light changes too much. Much level editing had to be done to adjust for the changing light.