
“…la Providence était le nom de baptême du Hasard,…“
[“…Providence was the baptismal name of Chance;…“]
-Nicolas Chamfort (1741-1794), Maximes et Pensées [Maxims and Thoughts] (1795, posthumous).
Four astronauts just launched toward the Moon for the first time in more than a half-century. To be clear, they won’t land on the Moon. They won’t even be going into orbit around the Moon. Rather, they will be following what is known as a “free-return trajectory”.
This is actually just an elongated orbit around the Earth that extends to a distance beyond the moon. Timed correctly, the passing Moon’s gravitational influence will then bend this Earth-orbit into a tight figure-eight that will send the spacecraft almost directly back. This was how the Apollo 13 astronauts managed to return to the Earth.
How the Earth’s single, relatively large Moon came to exist is still something of a mystery. No one really knows the exact mechanisms of how it was formed, or how it ended up in its current orbit. There are a number of theories. But every idea has some underlying technical difficulty.
Lunar rocks brought back from the moon during the Apollo missions appeared to show that the moon’s surface is made from material virtually identical to that found on the Earth. This means that both the Earth and the Moon had to have formed together in the same region of the early solar system, and that the moon wasn’t simply captured after forming elsewhere. But the physics doesn’t provide any simply way for this to have happened.
One popular idea, known as the “giant impactor”, proposes that a proto-planetary object about the size of Mars collided with the early Earth, mixing their crustal materials together while ejecting debris into an orbit around the Earth where it would eventually coalesce into the Moon. However, computer simulations show that this would have required a very precise collision. And the calculated overall spin of the resulting system wouldn’t account for the Earth/Moon system’s present “angular momentum”.
While the Artemis II crew won’t be staying at the Moon, they will get a view of its mysterious far side. This is an aspect not visible from the Earth due to the Moon being “tidally locked” to the Earth. This gravitational effect results in the Moon having a spin-rate that exactly matches the length of its orbit around the Earth. As a result, we always see the same side of the Moon.
The Moon’s hidden face, however, appears very different from the side that we can see from the Earth. Its far side is heavily cratered. And it also lacks the dark, lower-lying basins,
or “maria”, that comprise the cloud-like patterns humans have long described as a “man”, a “rabbit”, or as “seas”. Measurements made in 2012 also revealed that the Moon’s far-side crust is thicker, and that it includes an extra layer of material.
Several ideas have been suggested to explain the difference between the Moon’s near and far sides. Among them is that a dwarf planet in orbit around the sun collided with the moon some time after its formation. Simulations show that if an object about 480 miles (780 km) in diameter hit what is now the near side of the moon at around 14,000 miles-per-hour (22,500 kph), it would have resulted in a cloud of debris that would have fallen onto the Moon’s far side to a depth of from 3 to 6 miles (5 to 10 km).
Regardless, the moon’s existence has played a significant role in the development of life on the Earth. Its pockmarked face would have provided some shielding from large comet and asteroid impacts in the early solar system. And the early, much closer moon would also have created powerful tides, intermittently flooding tidal zones where prebiotic materials may have collected to form the Earth’s first life. And the moon also helps stabilize the Earth’s spin axis, keeping its seasons from fluctuating wildly.
However the Earth-moon system formed, it initially resulted in a much faster rate-of-rotation for the Earth, creating an about 5-hour day. This would have been fairly close to the physical limit of angular momentum for the formation of a planet within the proto-planetary disk. But the short days would have helped to stabilize planetary temperatures at a time when the the sun was at only about 70-percent of its present luminosity.
The Earth’s rapid spin, however, places a tidal drag onto the Moon. And this slowly transfers some of the Earth’s “angular momentum”, or spin-energy, into the Moon’s orbit. This gravitational transfer of energy gradually expands the Moon’s orbit while slowing the Earth’s rate of rotation. Even today, the Moon grows more distant from the Earth by about 1.5-inches per year as the Earth day lengthens by about 1.7-milliseconds every 100 years. In fact, an Earth day would currently be around 60-hours if not for various mediating influences from the Sun.
When the Moon first formed about 4.5-billion years ago, it was at a distance of only about 15,000 miles (24,000 km) from the Earth, and took a mere 11-hours to complete an orbit. But as the Earth’s rotation gradually slowed from its original 5-hour day to our present 24-hour day, the tidal energy transferred into the Moon’s orbit expanded it out to its present-day, almost 239,000 mile (385,000 km) distance. Today, about 80-percent of the Earth-moon system’s total angular momentum (its overall spin-energy) is concentrated in the Moon’s 27.3-day orbit. But this leads to an intriguing coincidence.
“Anatomically modern” humans have been on the Earth for only around 500,000 years. And their “pre-modern” ancestors who first developed larger brains and then migrated out of Africa only date back perhaps 1.8-million years. This represents such minds having perhaps looked toward the heavens in wonder for a mere 0.04%, or four ten-thousandths of the time in which the Earth/Moon system has existed.
And yet, humans have existed during a brief interval in which to witness both the Sun and the Moon covering the same arc in the sky.
The Moon is about 400 times smaller than the Sun. But at just this point in the Earth’s long history, the Moon’s orbit also just happens to have reached a distance from the Earth that’s about one four-hundredth the distance to the Sun. In fact, the balance is so close that just the difference in the Moon’s slightly elliptical orbit can create both “total” and “annular” eclipses of the Sun.
It’s a curious coincidence; and it won’t last forever. As the Moon continues to drift away from the Earth, it will also continue to appear smaller. And in about 300-million years, there will never again be a total solar eclipse.



and Charles Hampden-Turner’s “Maps of the Mind”, he came up with a sort of primitive artificial intelligence that would direct the actions of the game’s simulated humans.





And Darwin viewed the human-driven (by female choice) selection for both physiological fitness and compassion as an ongoing process central to the evolution of healthy civilizations.








Americans were jacked up on $5-trillion in “stimulus” while the doors to the mall were locked down with the economy. Then in 2021, the starting gun was fired and everybody swarmed at the merch like a mob of drunken looters at a burning Costco.

You must be logged in to post a comment.