Earlier maritime longitude.

Gauging longitude at sea became practical with the invention of the marine chronometer in the 1700s. Aside from having a chronometer appear earlier through the adoption of one of the development attempts is there any other way to have longitude determined at sea more or less reliably before the 16-1700s?

I've read that Galileo and Halley proposed celestial observation to gauge time, but these require telescopes which weren't much chop until the early 1600s and aren't very good on a rolling, pitching ship. What about water clocks or something, or a combination of other methods which would be considerably better than dead reckoning?
 
Actually, I just read a book about this! Aside from clocks, the other practicable idea was watching when the moon occluding different stars. If you have tables telling when this happens at a known longitude, you can calculate your own longitude. This depends on (1) knowing the moon's orbit (Kepler and Newton), (2) knowing the position of a lot of stars (Halley, c. 1678), (3) developing a practical observing instrument (Hadley, 1744, the octant), and (4) publishing enough accurate tables so that sailors who don't know much math can work through the process (a gradual process, including Bowditch, c. 1800). Once you jump-start the process by knowing the moon's orbit, I think all of these can happen relatively quickly, especially if you have a maritime power fund dissemination even earlier than Britain did iOTL.
 
Actually, I just read a book about this! Aside from clocks, the other practicable idea was watching when the moon occluding different stars. If you have tables telling when this happens at a known longitude, you can calculate your own longitude. This depends on (1) knowing the moon's orbit (Kepler and Newton), (2) knowing the position of a lot of stars (Halley, c. 1678), (3) developing a practical observing instrument (Hadley, 1744, the octant), and (4) publishing enough accurate tables so that sailors who don't know much math can work through the process (a gradual process, including Bowditch, c. 1800). Once you jump-start the process by knowing the moon's orbit, I think all of these can happen relatively quickly, especially if you have a maritime power fund dissemination even earlier than Britain did iOTL.

But don't you need an accurate chronometer to know when it happens at your latitude?
 
But don't you need an accurate chronometer to know when it happens at your latitude?
Longitude is equivalent to the difference between local time and London time. It is not hard to tell what the local time is by measuring the hiehgt of the Sun, and (IIUC) given the time of year you can tell based on the heights of various stars.

IOTL, the chronometer was just for obtaining London time. ITTL, London time is obtained by noting a lunar occultation, then looking up when that occultation happens with your astronomical tables. Basically, the Moon is the chronometer.
 
It is not hard to tell what the local time is by measuring the hiehgt of the Sun, and (IIUC) given the time of year you can tell based on the heights of various stars.
Exactly right. You can tell the time based on the date and the height of any star you recognize.

IOTL, the chronometer was just for obtaining London time. ITTL, London time is obtained by noting a lunar occultation, then looking up when that occultation happens with your astronomical tables. Basically, the Moon is the chronometer.
Again, exactly right. You watch the occulution happen, calculate the local time from the height of a star, and then look up the London time in a book. (With a chronometer, you'd calculate the local time from the height of a star and then look at your watch for the London time.) This was the method many sailors actually used iOTL for several decades until chronometers became cheap enough for them to buy.
 
Longitude is equivalent to the difference between local time and London time. It is not hard to tell what the local time is by measuring the hiehgt of the Sun, and (IIUC) given the time of year you can tell based on the heights of various stars.

IOTL, the chronometer was just for obtaining London time. ITTL, London time is obtained by noting a lunar occultation, then looking up when that occultation happens with your astronomical tables. Basically, the Moon is the chronometer.

Ah, now I understand. Thank you.
 
In Gavin Menzies' fictional masterpiece he goes on about Lunar Eclipses being able to determine longitude, but you couldn't rely on that when crossing the ocean.

Could the celestial observations be done before the invention of the telescope?
 
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