The Return of Darkness

With summer coming to an end in the British Isles we start the return to the dark skies of autumn and winter. Depending on where you are in the country you will have been without truly dark skies for many weeks, maybe even months, as summer evening twilight lasts throughout the night during the summer.

This all-night-long twilight is almost gone throughout the UK, indeed anywhere on the mainland UK can see astronomically dark skies around 1am at the moment. Only the furthest north outpost of the British Isles still doesn’t have that opportunity.

On the island of Unst, the furthest north of the Shetland islands, lies the UK’s furthest-north town, Skaw, at 60°49’N and 00°47’W. This tiny village will see astronomical darkness return at 0043 on 24 August, lasting only 46 minutes until at 0129 the sun’s light begins to creep into the sky again.

Midsummer sunset (at 2241) from Unst. Image Credit Brydon Thomason, Shetland Nature Ltd.

The last time that astronomical darkness was seen at Skaw was on 18 April, over four months ago! Indeed this settlement is so far north that between around 13 and 29 June each year they never get out of civil twilight, meaning that the sky’s bright all night long!

Compare this with the furthest south town in the British Isles, Saint Clement in Jersey, in the Channel Islands. Astronomical darkness returned to Saint Clement on 4 July this year, having been absent since 8 June; only four weeks without true darkness!

Such is the effect of differences in latitude that these two settlements, separated by 1299 km, have such hugely different seasonal swings between summer and winter.

 

 

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