But midsummer is also today.
If you take summer to be 1st June to 31st August, i.e. meteorological summer, then today is the middle day of the middle of those three months. To look at it another way today is the 46th day of summer and we still have 46 days to go, so we must be halfway through. Technically halfway is midnight tonight, this because June is shorter than August, but whichever way you jump midsummer is 16th or 17th July.
And midsummer is also 6th August.
The astronomical definition of summer is the period between the summer solstice and the autumn equinox. Summer is 94 days long so we're looking for the 47th day after the solstice and that's 6th August. Technically the gap is 93 days 15 hours and about 40 minutes, and technically the solstice moves around by a few hours every year, so sometimes the halfway point is on 7th August instead. But whichever day it is, 6th or 7th August, the good news is it's still three weeks away.
And midsummer is also tomorrow.
I'm basing this on temperature because it would make sense to think of midsummer as the warmest part of the year. Clearly this varies from year to year so the trick is to average out a lot of past temperature data and see where the warmest day is. I found a dataset for Oxford with a daily record going back to 1815 so have been able to calculate the average maximum temperature on every day from 1st July to 31st August. Here's the graph.
The average maximum temperature at the start of July is about 21°C, climbs to 22°C by the middle of July, gently drops back to 21.5°C until the middle of August and then quickly falls away. The day with the warmest average in this dataset is 25th July, a bit of an outlier, but the warmest week is 14th-20th July and that suggests 17th July is the height of midsummer.
And midsummer was also 20th June.
This is because 20th June was the summer solstice and by definition the summer solstice has the maximum number of daylight hours. It's seemingly weird that temperatures peak four weeks after maximum daylight but that's because before the solstice the land and the sea are still warming up.
So take your pick as to when Midsummer Day falls, but it could be last month, it could be next month or it could be right around now.
20th/21st June - maximum daylight
24th June - traditional Midsummer Day
14th-20th July - highest average daily temperature
16th/17th July - midpoint of meteorological summer
6th/7th August - midpoint of astronomical summer
