How far away did Tycho Brahe estimate that the fixed stars were? In multiples of our sun I imagine!

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    $\begingroup$ See Tychonic cosmological model: "Tycho used basic geometry to show that, assuming a small parallax that just escaped detection, the distance to the stars in the Copernican system would have to be 700 times greater than the distance from the Sun to Saturn." $\endgroup$ Oct 6, 2021 at 12:51
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    $\begingroup$ He didn't, in geocentric models the sphere of fixed stars was traditionally assumed to lie just beyond the orbit of Saturn (12.5 AU). Tycho only made estimates assuming the Copernican model (which he considered to be false):"in a Copernican universe, in order for annual parallax to be no more than a minute of arc (just falling under Tycho’s circle of general accuracy, and thus just evading detection), the distance to the fixed stars would have to be almost 7,000 A.U.", Graney And at such distance the stars had to be absurdly large. $\endgroup$
    – Conifold
    Oct 6, 2021 at 13:06
  • $\begingroup$ Saturn A.U. is 9.5414 $\endgroup$ Oct 6, 2021 at 13:12
  • $\begingroup$ sorry I see you mean 12.5 AU was the distance of the fixed stars? $\endgroup$ Oct 6, 2021 at 13:45
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    $\begingroup$ Of course even the nearest actual stars are many times farther than 7,000 AU distant, and many times larger than the size Tycho considered to be absurd. I think that one contemporary of Tycho Brahe (1546-1601), Giordano Bruno (1548-1600), believed the stars were distant suns with planets orbiting them, correctly as it turned out. $\endgroup$ Oct 6, 2021 at 16:33


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