[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".
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.
"The 6-pound cannon is fired everyday at 1 PM, from May to September."
Not at local noon?
Sweden user summer time, so we get up earlier during the bright part of the year.
So it's still local noon.
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?
Down and to the left