Although the first day of autumn isn’t until Sept. 22, Labor Day marks the unofficial end of summer.

We associate it with seasonal change because Labor Day is the last of the three so-called summer holidays (an assumption that’s also wrong because Memorial Day actually falls in springtime).

Labor Day also signifies that schools have reopened. To many of us, that’s all the proof we need: the school bells are ringing, after all, for the fall semester.

Want more evidence? Football season is here. Football is an autumn/winter sport. In Major League baseball, fans are starting to pay attention to wild card races, another sign that summer’s over.

Not satisfied that it’s actually fall? In some parts of the Midwest and East Coast, tree leaves are already changing colors. You’ll have to go north to see it, but it is happening.

The calendars are wrong by about three or four weeks. Winter unquestionably arrives before Dec. 21. We swing into spring before mid-March. Summer arrives before June 21.

California is a little different, but what’s new? In contrast with most of the nation, some of our hottest weather can arrive in September or early October. And what’s wrong with that? We like being different in California.

It’s what you think that really matters.

So despite our planet’s rotation around the sun and the socalled solstices and equinoxes, Labor Day means the end of summer.

And that’s final.