101 Darkless Nights
As an astronomer in the depths of a Scottish summer I have a long time to wait until darkness falls again. Between 5th May and 8th August this year – for 101 nights – the sky never becomes truly dark.
In order to get a truly dark sky you need to wait for the end of astronomical twilight, when the Sun sinks lower than 18 degrees below the horizon. However in particularly northern (or southern) latitudes there is a stretch of time during the summer when the Sun never gets this low, and the closer to the poles you are the longer this run of darkless nights can be.
So astronomers often go in to hibernation during these summer months, unless they want to observe or image those astronomical objects that don’t require true darkness: the moon, say, or the planets.
The Sun will next dip 18 degrees below the horizon (as seen from central Scotland) on 9th August around 1am, and then only for half an hour. As the days go on though it dips lower and for longer each night, and the hours of stargazing stretch until around the winter solstice we will have close to 12.5 hours of absolute darkness.
Plenty of time then to stock up before another long darkless summer.