Geology Through Literature:
Hans Christian Andersen's: The Galoshes of Fortune (1838)
The Galoshes of Fortune (1838)
"But all this is like the gait of a sloth, or the pace of a snail, in comparison with the speed of light, which travels nineteen million times faster than the fastest race horse.... The sunlight takes eight minutes and some odd seconds to travel nearly one hundred million miles."
The speed of light has currently been measured to be 3 x 10^8 meters per second (or more accurately 299,792,458 m/s).
The maximum speed of a race horse is ~44 miles per hour, or ~0.122 miles per second.
Converting, the speed of light is therefore ~670,000,000 miles per hour, or ~186,000 miles per second.
The speed of light then works out to ~15 million times the speed of the fastest race horse. Of course you must take into account that perhaps the fastest race horse of today is not the same as the ones in the mid-1800's. So if you had a race horse with a top speed of 35 miles per hour, then indeed, the speed of light would be 19 million times faster.
My big question here though, was when was the speed of light determined? This story was published several decades before Einstein, so who discovered how fast light moves and how?
The speed of light was actually determined almost 350 years ago. In 1676, the Danish astronomer Ole Roemer was studying Jupiter's moon Io. By studying the length of the eclipse during different times of the year, Romer hoped to determine an accurate orbital period of the moon. The orbital period, determined to be 1.769 Earth days, was watched by Romer over many years and he noticed that the time intervals between eclipses wasn't consisted. As the Earth moved towards Jupiter, the eclipses came earlier. As the Earth moved away from Jupiter, the eclipses came later. He estimated that there was a difference of 22 minutes between the two extremes. The cause of this delay, he determined, was the time that the light needed to cross space from the closer orbital point to the further orbital point. Dividing this time by the diameter of Earth's orbit, should give a fairly accurate value for the speed of light.
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| Illustration of how Romer determined the speed of light from the time of Io's eclipse. Image courtesy of AMNH by Diana Kline. |
This calculation was done by Dutch scientist Chistiaan Huygens, finding the value to be 131,000 miles per second (off by about 30%). The difference from the true value was due to inaccuracies in the time calculation by Romer (actually 16.7 minutes, not 22) and imprecise knowledge of the Earth's orbital diameter. Even with the incorrect speed determined, he was at least within the correct ballpark and his method for determining the speed of light was accurate.
The Moon
In a few seconds the watchman took in his stride the 260,000 miles to the Moon. As we know, this satellite is made of much lighter material than the earth, and is as soft as freshly fallen snow. The watchman landed in one of the numerous mountain rings that we all know from Doctor Maedler's large map of the Moon.
The novel Vanity Fair, happened to also bring up the topic of the distance to the moon and was published about 10 years after this book. I had broken down the early history of how the distance to the moon was calculated there.
For here I wanted to focus on three things. The first is the assumption here that the moon was made of a much lighter material than the Earth. We now know that the moon not made of softer and lighter stuff than the Earth, it is actually made of the same rocks as the Earth, and that is because it was formed from the Earth. Early in the history of the Solar System, there was a proto-Earth and another planet known as Theia. Theia crashed into Earth in its early history, melting both planets and combining them into one with a much smaller mass spinning off to form the moon. Because of this, chemically speaking, the moon is identical to the Earth. However, over time as the Earth has aged, it's rocks have differentiated from each other to produce varying rock types in different environments and depths, whereas the moon, being far smaller, cooled far quicker and is a much more homogenous mass.
The second question brought up is, is the surface of the moon really as soft as snow? The surface of the moon has been under constant bombardment of meteoroids that have been pummeling the lunar surface for nearly the entire 4+ billion history of the moon, leaving behind a layer of rock dust. It was even thought that the first people to land on the Moon in Apollo 11 could potentially sink right into the lunar soil because of this dust. That however, did not happen, since even though there is a fine layer of dust over the entire moon, the rocks, dust, and other debris have compacted over time just below the surface, providing a firm surface to stand, and land, on.
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| Copy of Mädler's original 1834 moon map. Image courtesy of Worthpoint. |
And the third thing is the map of Doctor Maedler. It turns out that shortly before this short story was written, that the first lunar map was published in 1834 by Johann Heinrich von Mädler. Originally broken up into four smaller section, it was eventually combined together into one very large map by 1837. This map gave us our first detailed, and widely available, map of the moon.
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| Mädler's 1837 version of the Moon map. High resolution version available at Geographicus. |
https://www.nhm.ac.uk/discover/how-did-the-moon-form.html
https://www.iop.org/explore-physics/moon/surface-features-moon#gref
https://www.worthpoint.com/worthopedia/mappa-selenographica-1834-lunar-map-142361918
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