What crucial pre-telescopic observation did Tycho Brahe make that demonstrated the heavens were not unchangeable?

Answer

Observing a supernova (Tycho's Nova) showing no measurable parallax

Tycho Brahe observed a supernova, or Tycho's Nova, which showed no measurable parallax, proving it was situated far beyond the Moon and thus challenging the ancient view of immutable heavens.

What crucial pre-telescopic observation did Tycho Brahe make that demonstrated the heavens were not unchangeable?

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