How Do Astronomers Fit an Expansion Rate—and Compare Disagreement?

Which measurements, calibrations, and model assumptions sit behind a single expansion number?

Fit a nearby distance–recession relation, revise its distance scale, then compare two dated expansion-rate inferences with their uncertainties and assumptions.

Concept art of irregular galaxy groupings separated by broad dark space, with a faint suggested connecting texture. — Vastward-generated concept art. The faint connecting texture is artistic, not an observation of dark matter or a map of measured expansion rates.

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