this 'summer' is the longest possible one you can have...

[dysfunctional press]

if you consider 'summer' to be the time(in the u.s.) from memorial day to labor day-

this year memorial day- the last monday in may, falls on the 25th, the earliest possible date- and labor day- the first monday in september, falls on september 7th the latest possible date...

so- make sure to make the most out of this summer- next year, it's 8 days shorter.