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March 11, 2002

Six months

It’s been six months since the attacks of September 11, which is as good an excuse as any to look back. Quite coincidentally, I recently reread my own writings from that week (1, 2, 3) which are very nearly as incoherent as I thought they were at the time.

My September 30 entry manages to present something resembling a rational argument. The major points: war is a terrible thing, even when it’s the best option available; we must learn how to minimize the damage possible from future attacks; understanding why they’re happening can help us prevent future ones from ever happening. Some people confuse explanation and understanding with excusing, which is unfortunate. Nothing can excuse or justify the attacks on the World Trade Center and Pentagon, but understanding the attackers may help us deal with future attackers and perhaps even prevent others from becoming terrorists.

If my tone at the time was overly skeptical of war, that was most likely a reaction to those in the media suggesting that the appropriate reaction was to nuke Afghanistan into a vast sheet of glass.

My October 17 entry describes my own brush with the anthrax scare and some sane security advice in the wake of the disaster.

I still remember the confusion of September 11. I learned about the attacks in my car, driving to work. It was some time before I realized that the plane they were talking about was a commercial airliner, and not a small, private plane. I remember walking past a silent piece of construction equipment in the parking lot at work and hearing the people on the radio shout in panic as the first tower collapsed—and not learning what had happened until I got to my office. Very little work got done that day, obviously. There were huge crowds watching CNN in the cafeteria, and later on the big screen down in the auditorium. People walked around looking dazed. Several people from the middle east—or who looked like they might be from the middle east—went home early out of fear of persecution.

I don’t know how many times I saw the planes hit, or how many times the towers collapsed. It didn’t seem real. Since then, I’ve visited the ruins, and I’m still not sure whether it’s really sunk in. Pictures of the new skyline don’t look wrong, but they don’t look like New York, either. #

How long is six months?

It’s pretty natural to figure that March 11 is six months after September 11. You start with September, check off six months, and you end up at March. It’s simple—as long as you’re talking about months.

If you look at it from a perspective of days, things are different. March is six months after September, and September is six months after March, but there aren’t the same number of days involved. In fact, “six months” can mean anything from 181 to 184 days, depending on which six months you mean.

Here’s a chart showing the length of a six month period starting in each month:


(Note that the numbers in the left column include February, and so are one day longer during leap year.)

Why the variation? First, all the months are not the same length—especially February. Second, half of 365 is 182.5, which means that you can’t divide the year into two equally-sized sets of days.

Aside from the problem with inconsistent length, there is are other difficulties with calculating six months. For example, what day is six months after March 31? Since there’s no September 31, you might guess October 1—but April 1 is six months after October 1, so April 1 is twelve months after March 31?

There are seven days with no obvious date six months later in our calender (six, if leap year is involved). One can reduce this number, but it can’t be eliminated entirely. For example, if we define “six months” to be “182 days”, we can specify a date that’s six months later for each day of the year. Unfortunately, applying the rule twice always gets us to one day before the day where we started.

We might try defining six months to be 182 days for the first 182 days of the year, and 183 days for the remaining 183. This means that each day has a defined date that’s six months later. Applying the rule twice always gets us back where we started—with one exception, December 31. Without redefining the length of the year, that’s the best we can do.

Not that we’d ever do that. Even with the seven holes, the current system is good enough for common usage and easily explained. (At least, more easily explained than the 182/183-day rule.) There may be twelve months in the year, but that doesn’t mean that six months needs to be exactly 182 days, 14 hours, 54 minutes, and 36 seconds. After all, if you’re going to be that precise, you need to define which year you’re talking about… #