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[Warning: bad joke ahead] Every day at noon a soldier fired a cannon to signal it was noon. A guy was curious as to how he knew when to fire the cannon. So he asked the soldier, who told him "the guy in the guard station gives me a signal, and I fire the canon". He asks the guy in the guard station how he knows when to signal, "I use the clock on the wall, a guy comes and sets it occasionally". He finds the guy who sets the clock and asks him how he knows what time it is, "I sync my watch to the clock in the town square, then set that clock from my watch". So he finds the guy who sets the town square clock and asks how he knows what time to set it to. "Oh, I just sync it to the noon cannon".

Haha I didn't realize this was a joke. It was, nearly word for word, a problem on my control systems final exam a few semesters ago!

I don’t know control theory but I think it wouldn’t work

Fun. It reminded me of the https://en.wikipedia.org/wiki/Clock_of_the_Long_Now, which uses a similar noon-sun mechanism for keeping the daily clock cycle accurate.

My neck of the woods on the front page!

Adelsnäs where the cannon is was built by some mining baron, as far as i remember.

Friendly reminder that if you are syncing your clock from marslight instead then remember that Mars, unlike Sol, isn’t always the same distance from us. Those light minute errors could mean you’ll miss the bus home!

I’m joking but this is also a real thing. For an example, see this code in the astrolib port used by SensorWatch’s “movement” project:

https://github.com/joeycastillo/Sensor-Watch/blob/e8f31beb70...

Doesn't Sweden have daylight savings time? How does that work with it being at 1pm every day?

That's why it's at 1pm instead of at noon. They don't fire it the rest of the year.

Ah, not firing it when it would be 12 is what I was missing

That's why it happens at 1 PM instead of 12 AM.

"The 6-pound cannon is fired everyday at 1 PM, from May to September."

Not at local noon?

Before they introduced Daylight Saving Time, it was probably at local noon. It would be at local noon if it were fired between October and March, but it's only May to September, so...

During summer, the peak sun altitude is at 1 pm (approximately) which makes it noon.

Sweden user summer time, so we get up earlier during the bright part of the year.

So it's still local noon.

At 12:00, the calibration people were busy nailing down the time, so the public sync signal was given at 1.

For navigational purposes you want your "noon" to be aligned with a known datum, and that often was Greenwich meridian.

Why would a cannon be used instead of, say, striking a bell? Does the sound travel better/further, or was it a display of wealth/status?

The sound is hard to mistake for anything else and travels better. Such cannons were used for synchronization of clocks on ships for navigation, among other uses.

But the sun isn't always at the same place at noon? So how is the magnifying glass aimed?

Same azimuth, different altitude. You could adjust the altitude angle daily, or just set the fuse along the north-south axis, and it will be lit in a slightly different place each day.

Down and to the left