Galileo asks: did Jupiter move east last night?

On 8 January 1610 Fate compelled Galileo to take his second look at Jupiter. This time all three little stars were west of Jupiter, whereas the night before two of them were east of Jupiter. That riased a huge question in his mind: Had Jupiter moved eastwards since the 7 January? Such a proper motion would be entirely at odds with the computations of astronomers.

My source is a new translation of Sidereus Nuncius http://bit.ly/7WsibK

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