It is 4.5 billion years ago. The Universe is in a chaotic state; the Earth has barely just coalesced from the debris flung out in a flattened disk spinning about our Sun.
At this point in time, about the sun rotates a flattened disk of matter which will later form the eight planets, many planetoids, asteroids, meteors etc.
Then, hurtling out of the depths of space flies Theia, a massive celestial body the size of Mars. It punches into our planet; the violence of the impact is barely fathomable. The crust and mantles of both planets are ripped apart and the cores of the two planets are fused together while massive amounts of debris are cast out into the ether. Much of it is collected by the gravity of the “new” earth while a disk of debris forms, much like that which spun around the sun (obviously on a much smaller scale). And it is that disk which over the next 10 – 100 million years coalesced into a boiling molten sphere that slowly cooled to eventually form our Moon.
Something very interesting happened over this period. As the moon cooled, the gravity of the much larger earth “dragged” the core of the moon off-centre by an estimated 480km, 20% of the moon’s radius. And so, naturally, as the core of the moon settled into its offset position, the spin of the moon was affected. Eventually, the moon stopped spinning and instead began to rock back and forth with the core dragging it back and forth. This rocking motion slowed over the next several millennia until finally, the moon settled into its current state with only one face turned toward our now blue planet. This process is known as “tidal locking” and is the reason why each and every single night we only bear witness to one side of our planet’s only natural satellite (and why Pink Floyd was able to gift us with their famous album, The Dark Side of the Moon.)
Now pock-marking the visible side of the moon are what are known as Lunar Maria, the Lunar Seas. The Moon’s Maria are named after their dark appearance, which reminded early astronomers of the dark, calm waters of the earth’s seas. There are a total of 31 maria on the moon, covering about 16% of its surface. These “seas” are concentrated on our side of the moon, the hemisphere that always faces the earth. This is because the crust on the near side of the moon is far thinner than on the far side because of the offset core, and over the millennia, as space debris battered the little planetoid, certain large enough meteorites punched through the crust into the shallow core and massive lava flows hundreds of kilometres wide surged over the surface. And because the moon is too small to retain an atmosphere there is no air, which means no wind, which means no weathering. That means that although these events may have occurred millennia ago we are still able to see the scars they have left behind. And these scars are what give those in the Northern hemisphere the Man in the Moon and those of us in the southern hemisphere, the Hare.
Can you see the hare in the moon? This may be upside down for any in the Northern Hemisphere but the picture below will be the right way around for you.
Each of these mares has a name, the most famous of which is likely the Sea of Tranquility, Mare Tranquillitatis, in which Apollo 11 touched down just 54 years ago. The largest sea, the Sea of Showers, Mare Imbrium, measures a spectacular 1100km. Just imagine a sea of molten lava 700 miles across. I greatly enjoy the names, especially those that make up the bulk of our Hare in the Moon, Mare Nectaris, the Sea of Nectar and Mare Fecunditatus, the Sea of Fertility make up the ears while the Mares Tranquillitatis (Tranquility) and Serinatus (Serenity) make up the head. The bulk of the body is made up of Mare Imbium (Showers) and one of my favourite names, Oceanus Procellerum, the Ocean of Storms, so named for its immensity is over 4 million square kilometres (1.5 million square miles), making it larger than the continent of Australia! It is the only ocean amidst the plethora of seas.
Each grey region is a different impact event and each consequently formed “sea” or “ocean” has a name.
And so, the next time you do some moon gazing (I encourage you to try using your binoculars), I hope you’ll see something completely new. It’s just one small part of the incredible beauty of our night sky.
Amazing, nearly unimaginable, this development of Earth and Moon.
Great pictures and very well explained.
Thanks Christa, I’m glad you enjoyed!
Thanks for the lesson Kyle. The moon and night skies are truly beautiful.
Very nice! The mare basalts are what geologists call flood basalts. Ironically, there are flood basalts close to you. The Karoo basalts run all along the eastern edge of South Africa (through Kruger Park) and turn in the northern part of the country to run east-west through the Karoo (hence, the name). They even extend into the eastern part of South America where they are called the Entendeka basalts. I actually used a lot of data from these basalts in my work when I was in South Africa. South Africa is blessed with fascinating geology!
Thanks, Paul, I’m definitely going to look into this!
If you are interested in basalts in other parts of the solar system, you might give a view to those on the asteroid Vesta. We just (yesterday) published a paper on those. The link is https://iopscience.iop.org/article/10.3847/PSJ/accb98. It’s open access so it’s free.
Busy reading this now, very interesting!
I have always been fascinated by astronomy and the vastness of the universe. Thank you for the fascinating insight into the Moon. I remember well Neil Armstrong’s first step – it is long past time when humans again walk on the Moon.
It definitely is, Jeff!
Loved this!!! Thank you for an unexpectedly beautiful post!🤩👍
Thank you for reading, Jenn, I’m glad you enjoyed it!
Hey Kyle, very interesting information. I never new about the gravity, core & reason we only see 1 face. Pretty fantastic if you think about it. Just curious if star trails are in your repertoire?
Hi Ann, the moon is a fascinating subject for sure. And yes, I do enjoy trying to capture star trails. As we go deeper into winter and the haze clears I’ll definitely be trying a few of those!
My goodness Kyle, that was a lot to take on board but really fascinating. I had known about the man in the moon as I do live in the northern hemisphere, but learned something new about what you see in the southern hemisphere. When I’m back in South Africa next year, hopefully there will be a full moon so I can take a look. Terrific blog!
Thanks so much, Denise. We look forward to seeing you again next year!
Very interesting Kyle, will certainly try using my binoculars to see if I can see someone new out there.
Hi Valmai, yes you must definitely try have a look at the next full moon!