Mount Wilson Observatory

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

George Ellery Hale had already built the largest telescope in the world once, at Yerkes Observatory in Wisconsin, before he decided to build a larger one somewhere else entirely. In 1904, with funding from the Carnegie Institution of Washington, he founded a new observatory on a 5,710-foot peak in the San Gabriel Mountains near Pasadena, California. The site was not chosen for its convenience. It was chosen because the air above it sat still, and a telescope is only as good as the atmosphere it looks through.

That choice paid off twice, in instruments before it paid off in discoveries. The 60-inch reflector, completed in 1908, was the largest working telescope of its day. Nine years later, the 100-inch Hooker telescope surpassed it, and held the record as the largest telescope on Earth until 1949. The mountain also carried three solar telescopes, towers built to study the sun rather than the stars, and later the CHARA array, an interferometer that combines several smaller telescopes to resolve detail no single mirror could capture alone.

Hale's stated purpose was simply to see farther and more clearly than anyone had managed before. What that stillness and that mirror made possible, in the hands of one astronomer working there less than two decades after the observatory opened, would turn out to be considerably larger than a bigger telescope.

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

In 1923, using the 100-inch Hooker telescope at Mount Wilson Observatory, Edwin Hubble identified variable stars in the Andromeda nebula whose brightness pattern let him calculate its distance. The number he got placed Andromeda far outside the Milky Way, settling a dispute astronomers had argued for years over whether the galaxy was the entire universe or one island among many. It was not. Andromeda, and everything like it, sat outside it.

Six years later, working with Milton Humason at the same observatory, Hubble went further. Measuring how the light from many distant galaxies was shifted toward the red end of the spectrum, and how that shift grew with distance, the two astronomers demonstrated that the universe itself is expanding, with galaxies receding from each other at speeds that scale with how far apart they already are. A universe that had been assumed static turned out to be in motion at every scale large enough to measure.

Both results depended on the same instrument and the same stretch of California mountain, chosen decades earlier for nothing more dramatic than the steadiness of the air above it. Mount Wilson's broader legacy beyond Hubble includes early evidence for dark matter, precise measurements of stellar diameters, and advances in spectroscopy, but the two Hubble results are the ones that changed what astronomers believed the universe was.