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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.
@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.
https://medium.com/@domchang/jupiters-moons-and-the-speed-of-light-e86ee8b96d
There was a better article specific to the history of navigation, but I can't find it now. It was a horrible pain in the ass to do ESPECIALLY while at sea, and then it was discovered there was discrepancy related to distance which led to a better estimation of the speed of light. This was just about the time seaworthy time pieces came online.
BTW, I'm using a link to your photo for flerf discussion, among other such images. It boggles my mind how one can't just use a pair of binoculars to make observations that shut down flerf, but people are weird like that.
@Romaq @freemo There is a good book by Dava Sobel "Longitude". Harrison the clock-maker lived close to where I live today.