June 22 is generally accepted as the longest day of the year (in the northern hemisphere), the summer solstice. And yet, in most of our experiences, the hottest days of the year tend to fall around the July-August timeframe. Why is that, if the day with the most sun exposure is way back in June, and the sun is steadily becoming more scarce by July-August?

I figure it's all about heat retention and dissipation. At some day in the year (before summer solstice), the sun during the day heats up (that side of) the Earth exactly as much as (that side of) the Earth loses at night.* This will happen twice a year -- once as days are getting longer, once as they shorten. For argument's sake, let's say those dates are May 22 and July 22.

So for all the days between May 22 and July 22, the Earth absorbs more heat than it gives off. Then, even though June 22 is the longest day, heat on the Earth is still building up to a peak around July 22 (as the hottest day). And then after that time, the sun won't be providing as much heat as the Earth loses, and temperatures will tend to cool down.** (Think integrals/derivatives, for you mathematicians and engineers.)

Does that make sense? Any holes that I haven't considered?

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* I'm assuming that the Earth's crust and second layer are generally heat insulators, so that one part of the Earth heating up doesn't affect other parts of the crust too much. For instance, San Diego's hot summer days don't melt off the ice caps. Fair assumption, I figure.

** The reverse will probably hold true, so that in our example, January 22 would be the theoretical coldest day of the year.