What critical piece of technology was essential for Edwin Hubble to successfully measure the distance to Andromeda?

Answer

The 100-inch Hooker Telescope

The 100-inch Hooker Telescope, the world's largest at the time and located at Mount Wilson Observatory, provided the necessary light-gathering power to resolve faint details needed for the measurements.

What critical piece of technology was essential for Edwin Hubble to successfully measure the distance to Andromeda?
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