Does The Sun Set On The British Empire?

British Empire map, 1886
Click to enlarge
Walter Crane’s map of the British Empire, 1886

In short, taking every thing into consideration, the British empire in power and strength may be stated as the greatest that ever existed on earth, as it far surpasses them all in knowledge, moral character, and worth. On her dominions the sun never sets. Before his evening rays leave the spires of Quebec, his morning beams have shone three hours on Port Jackson, and, while sinking from the waters of Lake Superior, his eye opens upon the mouth of the Ganges.

Caledonian Mercury, 15 October 1821, page 4: “The British Empire”

It’s noticeable, when reading the above, that none of the places it mentions by name still belong to the United Kingdom. The British empire is now much reduced in size; in fact, its overseas possessions are confined to a scatter of places that few people could reliably place on a map:

Overseas Territories
● Anguilla
● Bermuda
● British Virgin Islands
● Cayman Islands
● Falkland Islands
● Gibraltar
● Montserrat
● Pitcairn Islands
● Saint Helena (with Ascension & Tristan da Cunha)
● Turks and Caicos Islands
● British Indian Ocean Territory
● South Georgia and South Sandwich Islands
● British Antarctic Territory (in abeyance under Antarctic Treaty)

Dependent territory
● Sovereign Base Areas of Dhekelia & Akrotiri (Cyprus)

If you’re one of the people who would have trouble placing these names on a map, here’s a map:

British overseas territories
Click to enlarge
(Source of base map)

Cover of Britain's Treasure Islands by Stewart McPhersonAnd if you’d like to know more about all these places, I heartily recommend Stewart McPherson’s marvellous book, Britain’s Treasure Islands: A Journey To The UK Overseas Territories, as well as the accompanying BBC television series.

What stands out from the map above is that the UK still has the Atlantic, Caribbean and Mediterranean pretty well covered. There’s a solitary (and I do mean solitary) British possession in the Pacific, the Pitcairn Island group. (I’ve written about Pitcairn and its neighbouring islands a couple of years ago, when we were lucky enough to visit them.) And there’s another single possession in the Indian Ocean, the catchily named British Indian Ocean Territory (BIOT). BIOT occupies the whole of the Chagos Archipelago, and is inhabited entirely by British and American military personnel and contractors, based on the largest island, Diego Garcia. It used to be home to 2000 Chagossians, who were chucked out around 1970 to make way for the UK/US military installations. The poor Chagossians are still grinding through the courts attempting to get their homeland returned to them.

Anyway. Pitcairn and BIOT, which are a long way west and east of most UK territories, look like the key locations to examine when it comes to deciding whether the sun still “never sets on the British empire”. With Pitcairn’s time zone of GMT-8, and BIOT’s of GMT+6, there’s only ten hours of difference between the two territories, which should mean that the sun is visible from both locations for a couple of hours a day. But there’s a potential problem with the seasonal variation in day length—while BIOT sits close to the equator and won’t have much variation in the times at which the sun rises and sets, Pitcairn is south of the tropics, and so we can expect its sunsets to be noticeably earlier in June than they are in December.

So we’re going to need to plot daylight charts for the whole year. Here’s one for Greenwich:

Sunrise and sunset in Greenwich
Click to enlarge

Along the x-axis we have the months of the year, numbered from 1 to 12. On the y-axis, Greenwich Mean Time. The lower curve marks the time of sunrise, throughout the year, at Greenwich. The upper curve is sunset. The yellow area between the curves therefore represents the totality of daylight seen in Greenwich throughout the course of a year.

OK. Let’s superimpose the sunrise and sunset curves for Adamstown on Pitcairn, giving times in GMT:

Sunrise and sunset in Greenwich & Pitcairn
Click to enlarge

The Pitcairn sunrise and sunset curves are in red, and Pitcairn daylight extends a long way through the Greenwich night. But sunset on Pitcairn always occurs before sunrise in Greenwich, so there’s a brief period when the sun is shining in neither location.

Will BIOT, with its sunrise earlier than Greenwich, fill the gap? Here are the BIOT curves (calculated for Diego Garcia) added in green:

Sunrise and sunset in Greenwich, Pitcairn & BIOT
Click to enlarge

It’s a close-run thing. Pitcairn’s midwinter sunset on 21 June 2020 comes just 38 minutes after BIOT’s sunrise. Here’s a south polar view of the Earth on that date, capturing the brief period when both territories are in sunlight:

Diego Garcia and Adamstown both in sunlight on 21 June 2020
Click to enlarge
(Prepared using Celestia)

But there’s no doubt the chart is full of daylight, and the sun still never sets on the British empire!

2 thoughts on “Does The Sun Set On The British Empire?”

  1. Certainly , I would have been at a loss to name all the territories. Facetiously, I often refer to Canada as one of the ‘colonies “. It’s good to know the sun never sets…..

    1. I was actually prompted to write this one because I discovered our bank had my place of birth on record as the Akrotiri Sovereign Base Area, which would have been fabulously exotic if true. That led me to scroll through the list of British possessions to test my assumption that “Akrotiri” was the first in the list, alphabetically. And looking at the scattered islands in the list made me wonder about the sunset thing.

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