This is a photo I took 13 years ago of Jupiter and 4 of its moons (top). As a reference the image below is the simulated position at that same time.

Jeffrey Phillips Freeman  
Moons of Jupier Read more here: https://jeffreyfreeman.me/photography/jupiter-moons/ #Astronomy #Freemo

@freemo Incredible how sailors used the moons to find longitude with such primitive kit, ain't it.

@SteelFolk wait, they used the moons of jupiter? Thats news to me.

@freemo Yup. They looked different depending on where you were somehow and almanacks
were made to refer to. From a ship at sea before decent clocks were available.

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@freemo Once they had clocks that kept the time at home, they could tell their longitude at midday.

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