Remembering. (Jason DeCrow/AP)

Your birthday. Christmas. Halloween. Every year you go leafing through the calendar and they are there, waiting for you, with their accoutrements of streamers and cake or strings of tiny lights or masks and jack-o’-lanterns. Every year the sky looks about the same.

You mark them differently, as time passes. Of course you do. Your 12th birthday bears little resemblance to your 30th. The piñatas grow sparser. The ways of noticing that a day is different than the others change as you yourself do.

Perhaps that could be a working definition of a holiday. It is a day that it would feel strange to ignore.

It has been 11 years since that day in September, and it would still feel strange not to notice it. This is a day that travels with us, too.

These days, we are not only mourning. We are asking questions. We are reevaluating. We are far enough away that examination no longer smacks of disrespect.

Still, it stirs in the gut.

It was a Tuesday then, too. I was almost as young as the people who don’t remember it today. It is strange to think how old they are. The day is not an adequate or complete explanation for why things are as they are, but it is something. It is strange to imagine waking up in a world like this without even that to point to.

Every year the essays come tumbling out. There are jokes now, too. Some of them are even funny. There are all kinds of things. Last year there was an uncomfortable but definite vogue for these remembrances. It was the Big Year. Especially among Generation 9/11, in the peculiar position where the end of childhood coincided neatly with that morning in September, we all noticed it together. The day is going to be there, traveling with us, and the act of remembering is developing traditions of its own.

Every generation has one, it turns out. A day that you carry along with you, that you were not quite expecting to carry. When the generation passes, the day changes. I know that Dec. 7, 1941, is supposed to live in infamy, but for me it does so within the comfortable confines of a textbook. The shock travels both with us and away from us. The terrified stir in the gut, the fall smell of the air, the idea that this horror was even possible. They shine back at a remove, satellites launched 11 years ago that still beam back images from time to time. That is how things were before they became the way they are. It would still feel strange not to try to remember.