Union High senior Harli Stockwell impressed upon me how long 10 years is when it’s half your life.

I had asked her reaction to the killing of Osama bin Laden.

She was in fourth grade, doing her daily writing, when the teacher flipped on the news and the class started watching the terrorist attacks unfold.

“What I find astounding,” she said, “is the fact that some of the freshmen don’t even remember it at all. Some of them even asked what the twin towers were.”

Sept. 11 was a breaking story of cataclysmic proportions that sent newsrooms into overdrive.

I happened to be on vacation.

My mother-in-law phoned Sue to see what she made of a plane crashing into the World Trade Center.

Anchors improvised like jazz musicians. They can’t explain their compelling pictures.

See for yourself, they shrug, inviting us the unsuspecting closer for some snuff TV.

My attention turned to a jumbo jet bearing down like a moth to a light on the uninjured tower the talking heads don’t seem to notice.

When they cut to smoke billowing from the Pentagon and other planes go missing, my mind raced ahead, trying to remember the Tom Clancy plot terrorists seem to be following.

The office thought I’d relinquish missing inaction status and answer another bell, but this one was too big, too numbing to comprehend.

Since Labor Day weekend I’d been covering the spasm of gun violence and angry grief at the end of Rainbow Farm.

Toss in 15 unblinking hours in front of the TV on the kind of gorgeous day Mom would have shooed me outside to play and I was too emotionally drained to do anything but alternate between the bed, my chair and three sets, each tuned to a different network.

Jordan was supposed to play his first football game.

Uncle Eric dutifully drove over from Michigan City, Ind., to instead witness this demented “Groundhog Day” game film of the same broken play always ending in apocalypse.

Coach, call something different! I wanted to shriek the millionth time those gleaming icons of capitalism collapsed in a volcanic convulsion that blanketed everyone in ash, then turned into a roaring, snarling beast chasing terrified New Yorkers through their streets like a scene out of “Independence Day.”

As shock and grief give way to other emotions, we grasped at fortifying images for reassurance. Congress uniting on the steps of the unscathed Capitol to sing “God Bless America.”

Firefighters Sept. 12 hoisting a flag in the wreckage reminiscent of Iwo Jima.

Sue went downtown and bought every newspaper available.

The one I still remember was USA Today, usually so precise, bannering a death count it could only describe as “horrendous.”

No stories above the fold, just a fireball that could have been photographed by Zapruder and blown up so big every piece of debris is flash frozen in time.

Inside, 37 pages covered “America’s day of terror” by morning. Broadcasters’ battered bottom lines took a $100 million hit that first week to air news nonstop, shelving advertising and entertainment.

We welcomed new faces into our homes, particularly Ashleigh Banfield, and scrutinized the familiar in a new light. Funny men like David Letterman, letting Dan Rather weep.

Craig Kilborn — this was before Jon Stewart and Stephen Colbert — and Conan O’Brien banished comedy until time healed enough wounds to feel suitable again.

My own heart ached with a sadness thicker than the smoke.

There couldn’t have been a worse week to confront blood-spattered spectacles my lifelong hero wore Dec. 8, 1980, the night of his murder by a deranged autograph hound, but it was now or never. It always is.

Life happened while we were busy making other plans, but we went ahead with our Sept. 14 sojourn to Cleveland for “Lennon: His Life and Work.”

Jordan, Savannah and I studied handwritten lyrics dashed off on brown envelopes in the desolate museum.

Now my daughter lives there, starting a summer job Monday.

The Beatles soundtrack that has captivated me since I was 6 began on scraps of paper no bigger than those fluttering down on Lennon’s adopted home as the twin towers imploded. It took six years, eight months, to build them (1966-1973) and an hour and 42 minutes to erase them from the skyline, and we haven’t been the same since. That’s what Mayday meant to me, born the same year as bin Laden.