What is The Hubble Constant?

Measurements of the Hubble constant — the expansion rate of the Universe — is one of the great mysteries in science. What’s the question?

Edwin Hubble, early 20th Century astronomer, discovered the expansion of the Universe, starting a cosmological mystery that continues to this day. Image credit: NASA/ESA

Until just a century ago, our galaxy was thought to be the lone family of stars occupying the Cosmos. Philosophers, notably Immanuel Kant in the 18th Century, postulated the existence of other families of stars beyond our own. Unfortunately, their postulations — although…



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