The Moon :)

written by Alex Torres

The Moon is arguably the coolest thing in the night sky. It can sometimes get a lot of hate for being so bright that it washes out other interesting celestial objects (especially when it is full), but it more than makes up for that by being the most consistently and widely visible object in the night as well as Earth’s most intimate companion in the cosmos. In fact, the Moon has piqued human interest for as long as we have known human civilization to exist, even at times being worshiped as a god or goddess.

However, what I would like to discuss today is the Moon’s appearance from Earth. It is relatively common knowledge that the Moon is moving away from the Earth at roughly 1.48 inches per year due to tidal interactions between the two celestial bodies. Indeed, when the Moon initially formed around the Earth, it was most likely between 14,000 and 20,000 miles away from the Earth, 12 to 17 times closer than it is now at about 238,000 miles away on average. Though, interestingly enough, the Moon drifted away from the Earth much faster right after its formation than it does now. This is presumably because tidal forces between the Earth and the Moon were much stronger when they were closer, but regardless, after 600 million years, the Moon was already about 84,000 miles away from the Earth which would have made it about 2.8 times larger in the sky in terms of diameter and 8 times larger in terms of area. The relative size of the moon as it appeared from the Earth at different times are shown in the diagram below.

This time period also coincided with a period in the history of the Solar System called the Late Heavy Bombardment during which the Moon experienced a large number of significant impacts. What is interesting is that since the Earth is so much more massive than the Moon, leftover heat from its formation and the impact that presumably formed the Moon 4.5 billion years ago would have taken longer to dissipate from the Earth than from the Moon. Furthermore, since the Moon became tidally locked with the Earth within 100 million years of its formation, the near side of the Moon would always face the still incredibly hot Earth exposing it to significantly more heat than the far side. This is presumed to have made the crust on the near side of the moon thinner than on the far side because it took longer for the near side to solidify with so much energy radiating from the Earth, and with the large impacts of the Late Heavy Bombardment constantly bringing up molten mantle material from below the crust on the near side, the crust would only become thinner and thinner over time. This presumably caused significantly more volcanic activity on the near side of the moon than the far side and would lead to the formation of the lunar seas that we see today: the large patches of dark surface rock on the Moon that once were literal seas of molten rock.

By roughly 3.8 billion years ago when the Late heavy Bombardment was coming to an end, the Moon actually looked quite similar to how it does today minus a few craters that  occurred within the last 3.8 billion years. This means that at that time on Earth, you actually could have seen, more or less, what the Moon today would look like if it was much bigger in the night sky, making pictures like the one below not that crazy of a sight.

Dramatic panorama view of beautiful Big moon with twilight sky and clouds.Image of moon furnished by NASA.

Another interesting thing that I discovered whilst researching for this post is that the gravitational field of the moon is rather chaotic. As I mentioned earlier, the moon has been subject to numerous large impacts throughout its history, and the near side of the moon has a significantly thinner crust than the far side of the moon. This means that impacts to areas of the moon with thinner crust allow for dense mantle material to be drawn up to the surface and create areas of high mass concentration known as “mascons” among scientists. The effect of these mascons on the gravitational field of the Moon are so dramatic that it is incredibly difficult for objects to form stable orbits around the Moon as they constantly dip toward and drift away from the Moon during their orbits. This causes circular orbits to quickly degenerate into elliptical orbits that often even lead to collisions with the Moon.

Overall, despite the Moon being an object that I see almost daily, I have learned that there is still A LOT about it that I don’t completely understand, and honestly, I think that is what makes this mysterious celestial object still so beautiful even after 4.5 billion years

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