How, exactly, did Tycho Brahe do his measurements of (no) stellar parallax? All the descriptions of parallax that I have been able to find seem to talk about the change in position of a nearby star compared to background stars farther away, but as far as I know the Ptolemaic system assumed that the fixed stars were all at the same distance?

I guess I am looking for a description of how parallax measurements where actually historically done at Tycho's and Copernicus's time.

  • $\begingroup$ Yes, but that's not what I'm asking :) Sorry if I didn't express myself clearly. What I don't understand is that the descriptions include something like this image: starchild.gsfc.nasa.gov/Images/StarChild/questions/para.gif -- but surely in the Ptolemaic system "Star A" is one of the "Background Stars". I'm probably just being stupid in some way... $\endgroup$
    – thebear
    Commented Sep 5, 2013 at 10:24

1 Answer 1


he compared a supernova's position between dusk and dawn and could find no reason that it was an atmospheric event (it lay with the other stars). with the same technique he determined that his eponymous comet was further away than the moon but NOT among the stars.

he was firstly limited by naked eye accuracy in in using the parallax method--which can be used for objects up to a few thousand AU. secondly dusk to dawn comparison only takes the earths angular diameter as the parallax angle. he could have used the earths orbit (observations two seasons apart) but he wasn't in the heliocentric camp of Astronomers.


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