Hubble 1929: the pilot film
Our first pilot film, of Edwin Hubble's 1929 paper on the relation between distance and radial velocity: the original printing, the 24 nebulae in his Table 1, the straight line through them, and what he did and did not claim.
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Chapters
Transcript
PNAS, 1929
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?
The data
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.
The result
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 number
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.
What he claimed
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.
Explain a Paper
Every paper has a result worth seeing. Send us yours, and we will make its film. explainapaper.com
The paper
Hubble, E. (1929). A relation between distance and radial velocity among extra-galactic nebulae. Proceedings of the National Academy of Sciences 15(3): 168-173. doi:10.1073/pnas.15.3.168