Comment by Animats

13 hours ago

"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.

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.