Narration: synthetic voice. Script drafted with AI assistance.

In nineteen twenty-nine, Edwin Hubble published six pages on the extra-galactic nebulae, which we now call galaxies. His question: does a nebula's speed depend on its distance?

Speed came from each nebula's spectrum, its lines shifted by its motion. Distance was harder: he judged it mostly from how faint the stars inside looked. He had both for twenty-four.

Plot one against the other. A few near ones are even approaching. Beyond them, the farther away a nebula is, the faster it recedes, roughly along a straight line.

The slope, which he called K, was about five hundred kilometres a second per million parsecs. Today's value is nearer seventy: his distance yardsticks were miscalibrated, so every nebula came out too close.

Hubble was careful. He called the relation a first approximation over a restricted range, and thought it premature to discuss what it meant. Others read it as an expanding universe.

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