Mt Wilson: Two Discoveries That Changed the Universe

The road up to Mt Wilson climbs through chaparral and oak, and at the summit the air is thin enough, and the city lights of Los Angeles far enough below, that on clear nights you can see the sky the way people almost never see it anymore.

The one-hundred-inch Hooker Telescope was installed at Mt Wilson Observatory in nineteen seventeen, using a mirror blank that had been cast in France and shipped around Cape Horn because the Panama Canal was not yet completed. It was the largest and most powerful telescope in the world, and it would hold that distinction for thirty years.

On the night of October fifth and sixth, nineteen twenty-three, Edwin Hubble photographed a region of the Andromeda Nebula and identified a Cepheid variable star whose distance he calculated at approximately nine hundred thousand light-years. The Milky Way is about one hundred thousand light-years across. Andromeda was not a gas cloud inside our galaxy. It was another galaxy entirely. In his announcement to the astronomical community in nineteen twenty-four, Hubble proved that the universe was larger than anyone had imagined.

Five years later, in nineteen twenty-nine, Hubble published a second discovery. Using observations of multiple galaxies made at Mt Wilson, he demonstrated that the farther a galaxy is from us, the faster it is moving away. This relationship, now called Hubble's Law, was the empirical foundation for the expanding-universe model and, eventually, for the Big Bang.

Both discoveries came from this mountain. The Hooker Telescope still works. The view is still extraordinary.