In celestial navigation, how do you know what local noon is?

Question

I understand that to determine longitude, you need to compare local noon of the sun to a chronometer set to Greenwich noon. But how do you know when the local sun is at its highest point of the day?

Answer 1

Using the chronometer as a starting point, you figure out when noon is supposed to be.

You use the Sextant to measure the Declination (it has heavy, heavy dark glass for this) and monitor the sun until it hits the highest point. It actually appears to 'hover' there for a few seconds. Then you compare it to the chronometer. The distance it is off of from Greenwich time gives you the longitude.

Answer 2

set your watch to the greenwich signal at 10.am on the radio to get your exact time. local noon is exactly noon your time (12.00pm).
From where I am, Greenwich is 8 hours ahead