It's the day of the year with the earliest sunrise and the latest sunset, hence the greatest length of daylight.
If you check when that sunrise is you get a single time for London... my diary says 4.43am.
If you check when that sunset is you get a single time for London... my diary says 9.21pm.
But it's not quite as simple as that because London is a large city approximately 35 miles wide and 28 miles top to bottom.
And that's large enough for sunrise not to be at the same time in Upminster as it is in Uxbridge, indeed you may be surprised quite how large the difference is.
The first place in London to see the sun rise this morning was J28 of the M25 near Brentwood at 4.40am.
In central London, say at Trafalgar Square, the sun rose two minutes later at 4.42am.
The last place in London to see the sun rise this morning was Malden Rushett south of Chessington at 4.44am.
That's a four minute difference from one side of London to the other.
And here's what that looks like across the whole of London.
The yellow stripe, where a clock at sunrise would show 4.40am, includes Romford and Upminster.
The 4.41am stripe includes Enfield, Ilford and Bexley.
The 4.42am stripe includes Edgware, Westminster and Bromley.
The 4:43am stripe includes Uxbridge, Richmond and Croydon.
The 4.44am stripe includes Heathrow, Hampton and Chessington.
The red lines should actually be slight curves but my drawing software's not up to that, sorry.
Note how the stripes are parallel and just over 10 miles wide.
I explained why back in March at the spring equinox.
Back then the stripes were roughly north-south, but for the solstice they're very much NW/SE.
That's because the direction of sunrise shifts north as the solstice approaches.
You might expect something similar for sunset tonight.
And you'd be right, but also wrong.
Here's how that looks.
These stripes run NE/SW not NW/SE because the sun sets tonight in the northwest.
The light blue stripe, where a clock at sunset would show 9.20pm, includes Erith and Bromley.
The 9.21pm stripe includes Barking, Greenwich and Sutton.
The 9.22pm stripe includes Walthamstow, Westminster and Richmond.
The 9:23pm stripe includes Barnet, Harrow and Heathrow.
The 9.24pm stripe only includes Harefield and a few hamlets to the north.
I calculated these times using an online mapping tool called SunCalc.
This gives the precise time of sunrise and sunset anywhere on Earth to the nearest second.
For example at the Tower of London today sunrise was at 04.42:21 and sunset will be at 21.21:55.
Meanwhile at Trafalgar Square sunrise was at 04.42:33 and sunset will be at 21.22:07.
That's a 12 second difference for two places just over two miles apart.
Sunrise and sunset times are so place-sensitive that there's an 8 second difference from one end of Oxford Street to the other!
2026's earliest London sunrise (at M25 J28) was this morning at 4.40am and 25 seconds.
2026's latest London sunset (at Mill End nr Rickmansworth) will be tonight at 9.24pm and 17 seconds.
If you travel from one to the other you can enjoy London's longest period of daylight (16 hours 43 minutes and 52 seconds).
The longest possible period of daylight in one location is on the M25 near Crews Hill.
From sunrise at 04:41:31 to sunset at 21:23:09 is 16 hours 41 minutes and 38 seconds.
This is precisely because it's the northermost point in Greater London.
In December this motorway hard shoulder also has London's shortest possible day (7 hours 48 minutes and 45 seconds).
You can of course easily beat that by going to St Albans, or indeed Birmingham, or indeed Inverness.
But let's not get ahead of ourselves - enjoy the longest day across London today!
