Why doesn't it get dark at night in Aberdeen during the summer months?

During the summer months, the northern hemisphere is tilted towards the sun. The result of this is that days are longer in the northern hemisphere. The further north you are, the less the distance below the horizon it is. So while it may set, it is still quite bright, just like anywhere in the world shortly before the sun rises or shortly after it sets. At the North Pole in summer, the sun does not set. In Scotland it will set, but it is not far below the horizon, so on a cloudless night in particular it never gets completely dark, particularly towards the northern horizon.