Sunday, November 04, 2018
Today's the day that sunset in London slips over from "nearer 5pm" to "nearer 4pm". Yesterday the sun set at 4.31pm, and today it's 4.29pm. Sunset then remains "nearer 4pm" through the winter solstice and out the other side, until 21st January. Sorry, that's 11 weeks.
I can do similar calculations for "nearer 6pm", "nearer 7pm", "nearer 8pm" and "nearer 9pm", again all for London. Dates are for the next twelve months. Greenwich Mean Time is in blue, and British Summer Time is in red.
| Nearer 4pm | 4 Nov - 21 Jan |
| Nearer 5pm | 22 Jan - 23 Feb | 27 Oct - 3 Nov |
| Nearer 6pm | 24 Feb - 30 Mar | 5 Oct - 26 Oct |
| Nearer 7pm | | 9 Sep - 4 Oct |
| Nearer 8pm | 31 Mar - 5 May | 12 Aug - 8 Sep |
| Nearer 9pm | 6 May - 11 Aug |
"Nearer 6pm" is a GMT thing in the spring, but a BST thing in the autumn, because the dates we change the clocks aren't symmetrical. More intriguingly, "nearer 7pm" only happens in the autumn, and gets skipped over in the spring. In southeast England, 7pm sunsets are a September thing. Meanwhile we only get one week of 5pm sunsets in the autumn (it's just finished), but a full month of them later in the winter.
Let's do weeks.
| Nearer 4pm | 11 weeks |
| Nearer 5pm | 6 weeks |
| Nearer 6pm | 8 weeks |
| Nearer 7pm | 4 weeks |
| Nearer 8pm | 9 weeks |
| Nearer 9pm | 14 weeks |
The time of sunset changes fastest at the equinoxes, and slows down at the solstices, which is why the largest numbers appear at the top and bottom of the table. British Summer Time very much messes up the pattern in the middle. But if you need something to hang onto during the next 11 dark weeks, remember that "nearer 9pm" lasts a good bit longer than "nearer 4pm".
Update: In response to a comment from a reader in the Orkney Islands, where the time of sunset ranges from 3.14pm to 10.28pm, here's the Orkney data.
| Nearer 3pm | 6 weeks |
| Nearer 4pm | 8 weeks |
| Nearer 5pm | 4 weeks |
| Nearer 6pm | 6 weeks |
| Nearer 7pm | 4 weeks |
| Nearer 8pm | 6 weeks |
| Nearer 9pm | 7 weeks |
| Nearer 10pm | 12 weeks |
Update: A reader points out that Orkney is further west than London as well as a lot further north, making sunset a little later even before taking latitude into account. So here's the data for Newport, Wales, which has the same latitude as London but the same longitude as Orkney.
| | London
51½°N 0°W | Newport
51½°N 3°W | Orkney
59°N 3°W |
| Nearer 3pm | | | 6 weeks |
| Nearer 4pm | 11 weeks | 9 weeks | 8 weeks |
| Nearer 5pm | 6 weeks | 7 weeks | 4 weeks |
| Nearer 6pm | 8 weeks | 7 weeks | 6 weeks |
| Nearer 7pm | 4 weeks | 5 weeks | 4 weeks |
| Nearer 8pm | 9 weeks | 8 weeks | 6 weeks |
| Nearer 9pm | 14 weeks | 13 weeks | 7 weeks |
| Nearer 10pm | | 3 weeks | 12 weeks |
Update: A reader asks what the underlying pattern is, i.e. what the data would look like if we didn't put the clocks forward and stuck to GMT all year round. Here's London, GMT.
| Nearer 4pm | 11 weeks |
| Nearer 5pm | 9 weeks |
| Nearer 6pm | 9 weeks |
| Nearer 7pm | 9 weeks |
| Nearer 8pm | 14 weeks |
Update: I was expecting sunrise times to look similar but, because we yank them in the opposite direction when the clocks change, the spread looks very different. Here's sunrise in London.
| Nearer 5am | 14 weeks |
| Nearer 6am | 13 weeks |
| Nearer 7am | 14 weeks |
| Nearer 8am | 11 weeks |
Update: A reader has opened up the can of worms relating to what would happen if we no longer put the clocks back, i.e sticking to GMT+1 throughout the year. This is what'd happen to sunrise and sunset in London.
| Nearer 5am | 14 weeks |
| Nearer 6am | 9 weeks |
| Nearer 7am | 9 weeks |
| Nearer 8am | 9 weeks |
| Nearer 9am | 11 weeks |
| | | Nearer 5pm | 11 weeks |
| Nearer 6pm | 9 weeks |
| Nearer 7pm | 9 weeks |
| Nearer 8pm | 9 weeks |
| Nearer 9pm | 14 weeks |
|
Update: Another reader mentions Singapore, which lies one degree north of the equator. Here the maximum difference in sunset times is only thirty minutes, the earliest being in November (6.50pm, today!) and the latest in February (7.20pm). Reasons for this are complicated.
n.b. Geography dictates that Singapore's time zone should be GMT+7, whereas in fact it adheres to GMT+8 to match Malaysia, China and the Philippines, which is why sunset is always nearer 7pm than 6pm.
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