A note from George Johnson, Miss Leavitt’s Stars: The Untold Story of the Woman Who Discovered How to Measure the Universe (New York and London: W. W. Norton and Company, 2005), 7-8:
[A]stronomers can say with some confidence that our own galaxy, the Milky Way, is more than 100,000 light-years from end to end and that Andromeda, the galaxy across the street, is 2 million light-years away. These and several other galaxies form our “Local Group.” The neighborhood. Just across town are other conglomerations of galaxies like the Sculptor group and the Maffei group, nearly 10 million light-years in distance. A little farther are the Virgo and Fornax clusters, lying some 50 million light-years from the Milky Way. Even if these were miles, the numbers would be staggering. A single light-year is almost 6 trillion miles.
We still haven’t left our hometown “supercluster,” a galaxy of galaxies a full 200 million light-years across. Beyond it lie more superclusters, stretching to the edge of the visible universe, 10 billion or so light-years from home.
Faced with so grandiose a vision, it is a little surprising to learn that as recently as the 1920s many astronomers thought the Milky Way was the universe. Whether there was anything beyond it was a matter of scholarly debate. What are now taken to be vast galaxies similar to our own were dismissed as small nearby gas clouds, insignificant smudges of light.
I’ve recently been sharing a number of such passages in an attempt to help readers — and, emphatically, to help myself — grasp to at least some small and insignificant degree the unimaginable vastness of the cosmos.
“The most beautiful thing we can experience is the mysterious. It is the source of all true art and science. He to whom the emotion is a stranger, who can no longer pause to wonder and stand wrapped in awe, is as good as dead —his eyes are closed. The insight into the mystery of life, coupled though it be with fear, has also given rise to religion. To know what is impenetrable to us really exists, manifesting itself as the highest wisdom and the most radiant beauty, which our dull faculties can comprehend only in their most primitive forms—this knowledge, this feeling is at the center of true religiousness.” (Albert Einstein)
“The heavens declare the glory of God; and the firmament sheweth his handywork.” (Psalm 19:1)