[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".
Wouldn't this setup actually work though? At least if it's a proper sundial cannon.
Most components of that system are mechanical clocks, which do keep the time on their own, they just drift. The only exception is the gunner who fully relies on an external time signal.
So if that were all, the system would work for a while, but slowly drift and become ever more inaccurate, until it basically has nothing do do with the actual time anymore.
However, the gunner does not always operate the cannon: He only does on cloudy days. On sunny days, the cannon operates itself, using the time signal of the actual sun - which is then passed through the chain and let's the mechanical clocks resync to "sun time".
So in effect, the system's time signal comes from the sun. The rest is just an overly complicated way to "interpolate" the time if the sun is not visible or not at noon.
(Now I also wonder if someone ever build a "self-syncing" mechanical clock - e.g. for a clocktower - using this principle: Use a standard clockwork, but add some mechanism that resets the clock to noon when a focused beam of sunlight hits a certain point.)
So the mechanism of a uniaxial gimbal (as pictured in the examples at end of article, and presumably manually adjusted) holding the magnifying glass would seem to introduce some error over the course of a year. But I like the concept, having some weird affinity for automation based on low-tech / earlier-tech principles.
Only when used in conjunction with a standardised 'mean-time' 24 hour clock. If you plot the position of the sun at the same mean clock time, then sometimes the sun will be ahead, sometimes behind.
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:
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...
Because it is way more fun, unique and create a much better cloud of smoke. A great way to show off your wealth at the time it was built. Things does not always have a technical reason to be chosen. People are silly.
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.
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.
[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".
[Warning: overanalysis of bad joke ahead]
Wouldn't this setup actually work though? At least if it's a proper sundial cannon.
Most components of that system are mechanical clocks, which do keep the time on their own, they just drift. The only exception is the gunner who fully relies on an external time signal.
So if that were all, the system would work for a while, but slowly drift and become ever more inaccurate, until it basically has nothing do do with the actual time anymore.
However, the gunner does not always operate the cannon: He only does on cloudy days. On sunny days, the cannon operates itself, using the time signal of the actual sun - which is then passed through the chain and let's the mechanical clocks resync to "sun time".
So in effect, the system's time signal comes from the sun. The rest is just an overly complicated way to "interpolate" the time if the sun is not visible or not at noon.
(Now I also wonder if someone ever build a "self-syncing" mechanical clock - e.g. for a clocktower - using this principle: Use a standard clockwork, but add some mechanism that resets the clock to noon when a focused beam of sunlight hits a certain point.)
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
That may be precisely the problem.
Interesting. Solar noon forms an analemma.
https://en.wikipedia.org/wiki/Analemma
So the mechanism of a uniaxial gimbal (as pictured in the examples at end of article, and presumably manually adjusted) holding the magnifying glass would seem to introduce some error over the course of a year. But I like the concept, having some weird affinity for automation based on low-tech / earlier-tech principles.
> Solar noon forms an analemma.
Only when used in conjunction with a standardised 'mean-time' 24 hour clock. If you plot the position of the sun at the same mean clock time, then sometimes the sun will be ahead, sometimes behind.
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...
"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...
Sweden user summer time, so we get up earlier during the bright part of the year.
So it's still local noon.
During summer, the peak sun altitude is at 1 pm (approximately) which makes it 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.
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.
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?
Because it is way more fun, unique and create a much better cloud of smoke. A great way to show off your wealth at the time it was built. Things does not always have a technical reason to be chosen. People are silly.
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