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Old 10-08-2019, 04:55 AM
The Stafford Cripps is online now
Join Date: Oct 2001
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What practical methods did Kepler et al use to compute orbits?

How did they convert 2D maps into 3D theoretical models, eg when Herschel discovered Uranus?

For a given planet or comet, I'm guessing that the raw data was nightly recordings of the object's apparent position against the fixed stars behind it, so that they had a record of the object's co-ordinates through time. These were presumably some measure of ecliptic latitude and longitude. They could then plot the object's course onto paper, to show its angle compared with the ecliptic, its periods of retrograde motion etc.

My main question is: how did they convert this data into units for applying trigonometry, or whatever other maths were required?

Is there a unit of speed that is used, eg "it averaged 7 units a day eastwards for 8 days at an angle of 2.4 degrees and then slowed down to 5 for 3 days" or something like that? What would the next stage be? (Or the first stage, if my assumptions are wrong?). Did they have to draw it out on paper or could they work out the orbit straight from the co-ordinates?


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