100-inch Telescope at Mt. Wilson Observatory

On our visit to Mount Wilson Observatory, we met a celebrity of sorts. The final stop of the tour was the telescope Edwin Hubble used. Hubble, as in the man the Hubble Space Telescope was named after. Standing inside the dome and looking through the same instrument he once worked with made time feel suspended. My mind kept circling the idea that some of humanity’s greatest discoveries about the universe were made right there, in that very room.

Hubble’s most famous contribution was the discovery that other galaxies are moving away from us, and that those farther away are moving faster. This revealed that the universe itself is expanding. When Albert Einstein visited Mount Wilson in 1930, he saw the evidence for himself and publicly supported Hubble’s conclusions. In that moment, the observatory became not just a workplace but the birthplace of modern cosmology.

That history is inseparable from the telescope itself. The 100-inch Hooker Telescope was conceived after the success of Mount Wilson’s earlier 60-inch instrument. It was funded initially by John D. Hooker and later supported by the Carnegie Institution. The massive mirror blank was ordered from France in 1906, but building a single piece of glass at that scale was unprecedented and led to years of delays. Engineers also had to invent new solutions for the telescope’s weight and thermal stability, including mercury flotation bearings and water cooling coils to keep the mirror at a stable temperature. Even the dome was carefully designed, with a dual shell to limit heat buildup that could distort observations.

When the telescope finally saw first light in 1917, it became the largest operational telescope in the world. Over the following years, it transformed our understanding of the universe. Using this instrument, Hubble identified Cepheid variable stars in the Andromeda Nebula, proving it was actually another galaxy far beyond the Milky Way. He later measured the redshifts of galaxies, showing that the universe is expanding. In 1919, Albert Michelson also used the telescope to make the first direct measurement of a star’s diameter, that of Betelgeuse.

The Hooker Telescope has been upgraded, restored, and preserved through the decades. After a period of inactivity in the late twentieth century, it was brought back into operation for public viewing and limited research. Today, it stands as both a scientific instrument and a living piece of astronomical history. Sitting inside that dome felt surreal. It was a reminder that discovery is not abstract. It happens in real places, through human hands, curiosity, and persistence. The inspiration I felt there was only the beginning.

References:

Mount Wilson Institute. (n.d.). Building the 100-inch Telescope. Mount Wilson Observatory. Retrieved from https://www.mtwilson.edu/building-the-100-inch-telescope/This is an official Mt. Wilson page documenting the planning, engineering, challenges, and assembly of the 100-inch Hooker telescope. It’s a strong institutional primary source on its mechanical, optical, and historical development.

Mount Wilson Institute. (n.d.). The 100-inch Telescope. Mount Wilson Observatory (Discovering Mount Wilson series). Retrieved from https://www.mtwilson.edu/discovering-mount-wilson-chapter-14-the-100-inch-telescope/This “Discovering Mt. Wilson” institutional series provides a timeline and narrative of the 100-inch telescope’s construction, early operations, and later history, drawing from the observatory’s archives.

Mount Wilson Institute. (n.d.). 100-inch Telescope (virtual tour / public info). Retrieved from https://www.mtwilson.edu/vt-100-inch/This page describes the 100-inch’s features, its public-access modes, its optical configurations and its periods of inactivity and restoration, from the observatory’s own materials.