• Days are getting shorter.
• Nights are getting longer.
• Evenings are getting shorter.
• Mornings are getting shorter.
But only two of these are true from Monday.
One isn't true until next Friday.
And one is already true today.
Here's why.
Let's start with the length of the day, because that's the easy part.
The amount of daylight doesn't change much at this time of year*.
But it does increase up to the solstice and decrease afterwards
(because that's how solstices work).
* In London the amount of daylight is...
...more than 16 hours for 57 days
...more than 16 hours 30 minutes for 26 days
...more than 16 hours 35 minutes for 17 days
...more than 16 hours 38 minutes for 7 days
LONDON
Date
Daylight
change
Wed 16 Jun
16h 37m 18s
+33s
Thu 17 Jun
16h 37m 43s
+27s
Fri 18 Jun
16h 38m 05s
+22s
Sat 19 Jun
16h 38m 20s
+15s
Sun 20 Jun
16h 38m 30s
+10s
Mon 21 Jun
16h 38m 33s
+03s
Tue 22 Jun
16h 38m 30s
-03s
Wed 23 Jun
16h 38m 21s
-09s
Thu 24 Jun
16h 38m 06s
-15s
Fri 25 Jun
16h 37m 45s
-21s
Sat 26 Jun
16h 37m 18s
-27s
Until Sunday tomorrow always has more daylight than today (even if it's only three more seconds).
But after Monday the days start getting shorter again.
Ditto the shortest night is Sunday evening/Monday morning (at a mere 7 hours 21 minutes 27 seconds).
But after Monday the nights start getting longer again.
Where it gets complicated is sunset and sunrise.
And why it's complicated is because the Sun isn't usually overhead at noon.
LONDON
Date
Sun highest
change
Wed 16 Jun
13:02:24
+12s
Thu 17 Jun
13:02:36
+12s
Fri 18 Jun
13:02:49
+13s
Sat 19 Jun
13:03:01
+12s
Sun 20 Jun
13:03:13
+12s
Mon 21 Jun
13:03:25
+12s
Tue 22 Jun
13:03:37
+12s
Wed 23 Jun
13:03:50
+13s
Thu 24 Jun
13:04:02
+12s
Fri 25 Jun
13:04:14
+12s
Sat 26 Jun
13:04:25
+11s
There are only four days a year when the sun is highest in the sky at noon GMT...
...one in mid-April, one in early June, one at the start of September and one at Christmas.
It's all because a) the Earth is tilted on its axis b) its orbit is an ellipse, not a circle.
I've blogged about this before, aka 'the equation of time', so I'll not go over it all again.
During June the time of solar noon nudges forward by about 12 seconds a day.
Normally 12 seconds is an irrelevant amount in the grand scheme of things.
But at this time of year changes in daylight are less than 24 seconds daily...
...which means changes in sunrise and sunset are less than 12 seconds daily...
...so the steady advance of solar noon skews the times of sunrise and sunset.
Example(17th June → 18th June)
Between today (16h 37m 43s) and tomorrow (16h 38m 05s) daylight increases by 22 seconds.
This splits to make sunrise 11 seconds earlier and sunset 11 seconds later.
But solar noon is 12 seconds later, which has to be combined with the other changes.
The net result on sunset is for it to be 23 seconds later.
And the net result on sunrise is for it to be 1 second later, not earlier.
LONDON
Date
Sunrise
Sunset
Wed 16 Jun
04:43:46
21:21:03
Thu 17 Jun
04:43:44
21:21:28
Fri 18 Jun
04:43:46
21:21:51
Sat 19 Jun
04:43:51
21:22:11
Sun 20 Jun
04:43:58
21:22:28
Mon 21 Jun
04:44:09
21:22:42
Tue 22 Jun
04:44:22
21:22:52
Wed 23 Jun
04:44:39
21:23:00
Thu 24 Jun
04:44:59
21:23:05
Fri 25 Jun
04:45:21
21:23:06
Sat 26 Jun
04:45:46
21:23:04
So, sunrise starts getting later after today.
But sunset only starts getting earlier after next Friday.
That's a difference of eight days...
...four days before the solstice and four after.
n.b. This isn't special to London.
It applies across most of the country and at similar latitudes.
Precise times will be different but the 'turn-round' dates should be much the same.
n.b. solstices move slightly from year to year, so dates aren't always identical.
Finally, let me combine columns from my three earlier tables.
Date
Change in daylight
Change in solar noon
Sunrise
Sunset
Wed 16 Jun
+33s
+12s
04:43:46
21:21:03
Thu 17 Jun
+27s
+12s
04:43:44
21:21:28
Fri 18 Jun
+22s
+13s
04:43:46
21:21:51
Sat 19 Jun
+15s
+12s
04:43:51
21:22:11
Sun 20 Jun
+10s
+12s
04:43:58
21:22:28
Mon 21 Jun
+03s
+12s
04:44:09
21:22:42
Tue 22 Jun
-03s
+12s
04:44:22
21:22:52
Wed 23 Jun
-09s
+13s
04:44:39
21:23:00
Thu 24 Jun
-15s
+12s
04:44:59
21:23:05
Fri 25 Jun
-21s
+12s
04:45:21
21:23:06
Sat 26 Jun
-27s
+11s
04:45:46
21:23:04
The yellow zone is the crucial part.
It's where the daily change in daylight, halved, is less that the advance of solar noon.
It lasts precisely eight days.
Hence the earliest sunrise and latest sunset are eight days apart.
A similar thing happens around the winter solstice in December.
This time the earliest sunset is usually eight days before the solstice...
...and the latest sunrise is eight days after the solstice.
The much bigger range is because solar noon is advancing by about 30 seconds a day, not 12.
A fabulous consequence of this is that evenings get shorter for 171 days (25 Jun → 13 Dec).
But evenings then get longer for 194 days (13 Dec → 25 Jun).
So the optimistic 'half' of the year is 23 days longer than the glum half.
In conclusion...
• Days are getting shorter from Monday.
• Nights are getting longer from Monday.
• Evenings are getting shorter from next Friday.
• Mornings are getting shorter from today.
But if you're up really early tomorrow morning, I doubt you'll notice.
