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Physics, Astronomy & Cosmology / Re: How do we tell the time via the 4 moons of Jupiter?
« on: 30/08/2021 00:04:33 »
By the time of Cook's voyages (around 1777), clock technology had improved enough that a mechanical clock could keep good time at sea, and they weren't so dependent on seeing Jupiter to calibrate to GMT.
- They were still dependent on seeing the Sun or Moon to find their local time. Local time is also vital for navigation.
Yes every 15 degrees west of Greenwich (360 degree turn of planet/ 24= 15) meant if e.g. you knew it was noon in Greenwich and you knew it was 1400 hours where you were at sea then you would consult the grids on your map (you'd be 2 grids west of Greenwich in that example).
How would you know what time it was at sea? Position of Sun from east to west? How about at night?