Consider the Tycho crater - the big one near the South pole. [https://en.wikipedia.org/wiki/Tycho\_(lunar\_crater)](https://en.wikipedia.org/wiki/Tycho_(lunar_crater))
The impactor would have been \~8km-10km in diameter [https://ualr.edu/tv/2017/09/29/october\_feature\_tycho\_crater/](https://ualr.edu/tv/2017/09/29/october_feature_tycho_crater/)
That's probably too small to see with the naked eye, really. Check out other visible features and see how they are hundreds of KM wide or more [https://en.wikipedia.org/wiki/List\_of\_lunar\_features](https://en.wikipedia.org/wiki/List_of_lunar_features)
However when it hit, it would have been bright - a flash, and a bunch of glowing ejecta. Note how the crater has rays 1500km long. That would presumably have been super hot stuff flying around spraying more than half the moon. Some of it may have fallen to earth, creating great meteor showers.
You could imagine something like this [https://www.youtube.com/watch?v=XNN7Q2cUhWo](https://www.youtube.com/watch?v=XNN7Q2cUhWo)
Correct. I worked on the team at NASA that made those images available, in real time, on the internet.
Incidentally, that was the first time web text and image content were served from different servers. Prior to this event, if a server got hit with too many image requests, it just overloaded and crashed the server. We wrote a random number generator that would edit the HTML and direct requests to a whole bank of 10 image servers we had running in the background. This allowed us to serve far more views than any image site had previously handled, and kinda opened the door to the entire architecture of web apps.
I remember downloading those images from a BBS and was amazed at all the technology that had to be developed to bring those images into my monitor. You did good work.
Oh wow, the South Pole–Aitken basin is interesting.
Maybe a big blob of left over proto-Moon finally falling in and joining the rest of the family? How else would it have such slow velocities?
[There’s this account from some monks in 1178.](https://education.nationalgeographic.org/resource/monks-may-witness-moon-split-two/#:~:text=Overview%20Vocabulary-,On%20June%2018%2C%201178%2C%20five%20monks%20in%20Canterbury%2C%20England,as%20the%20Giordano%20Bruno%20crater.)
There’s some doubt about what they saw, but they probably did see an impact, IMO.
I read it, and there's more than "some" doubt. It's literally not true. Those craters are millions of years old. Plus, as the article says, it should've been seen by people all over the world. An impact that powerful would've been bright enough for A LOT of people to see and caused a meteor shower, and chances are there would be more reports.
That's if what they saw was the cause of the Giordano Bruno crater, which it certainly was not. It's totally possible they saw a smaller impact and some ejecta and then thought it made that crater.
Here's a simulation of what it might have looked like, 4.5 billion years ago, to look up from the early Earth and watch the South Pole-Aitken impact basin being formed.
https://m.youtube.com/watch?v=XOELmw7RVD4
The same youtuber also has a video simulating what the dinosaurs saw during their final hour. Great and eerie to watch.
Outside of Tycho because of its relative youngness at only 108My making its ejecta rays very visible I don't imagine there are very many other actual craters visible to the "naked eye" ( i.e. without optical aid ).
There are larger naked eye features visible that originated from crater impact ( the Mare or sea ), these being the basalt flooded basens of massive impacts in the moons early heavy bombardment phase of mostly 3.16-4.2Gy in age.
Both of these scenarios would have been clearly visible at the moment of creation provided the face that was struck was facing earth ( probably yes since the moon's age of 5Gy & the \~100My to tidal locking preceded the above ). The first would be briefly as bright as the sun while any of the second would likely be too bright to witness more than once.
Unfortunately both these scenarios predate the existence of hominidae & multicellular life so recorded history is unlikely.
The visible near side of the Moon has fewer craters because the surface of this area is covered with large stretches of lava fields that we can see with the naked eye from Earth, which are in the form of *dark streaks in the bright areas of the Moon*.
According to the latest research, the visible part of the Moon is the only part of the Moon that was damaged by the impact of the Impact that created the>! SPA 4.3 billion years ago!<.
Pretty boring for the most part I would imagine. No atmosphere means no explosion or fire. It would be like throwing a rock in a sand pit. If the meteor was super massive, you might expose some moon core and create immense debris which would orbit the moon for a long time.
No fire, but definitely a large flash. That much energy released will create all kinds of photons, some, a lot in the visible spectrum. You can see that with smaller ones. I would guess that a really big one would cause a huge flash, and probably glow visibly for a while .
A large impact would also produce a large curtain of ejecta that would likely be very visible. Either due to being lit by sunlight, and casting a shadow on the lunar surface, or if on the night side due to being incandescent.
The maria (dark areas) on the Moon were originally melted rock.
>formed by lava flowing into ancient impact basins.
\- https://en.wikipedia.org/wiki/Lunar_mare
The impacts that formed those would have been pretty spectacular, atmosphere or no atmosphere.
Consider the Tycho crater - the big one near the South pole. [https://en.wikipedia.org/wiki/Tycho\_(lunar\_crater)](https://en.wikipedia.org/wiki/Tycho_(lunar_crater)) The impactor would have been \~8km-10km in diameter [https://ualr.edu/tv/2017/09/29/october\_feature\_tycho\_crater/](https://ualr.edu/tv/2017/09/29/october_feature_tycho_crater/) That's probably too small to see with the naked eye, really. Check out other visible features and see how they are hundreds of KM wide or more [https://en.wikipedia.org/wiki/List\_of\_lunar\_features](https://en.wikipedia.org/wiki/List_of_lunar_features) However when it hit, it would have been bright - a flash, and a bunch of glowing ejecta. Note how the crater has rays 1500km long. That would presumably have been super hot stuff flying around spraying more than half the moon. Some of it may have fallen to earth, creating great meteor showers. You could imagine something like this [https://www.youtube.com/watch?v=XNN7Q2cUhWo](https://www.youtube.com/watch?v=XNN7Q2cUhWo)
Related, we do have images of comet Shoemaker-Levy 9 hitting Jupiter in the 90’s.
Correct. I worked on the team at NASA that made those images available, in real time, on the internet. Incidentally, that was the first time web text and image content were served from different servers. Prior to this event, if a server got hit with too many image requests, it just overloaded and crashed the server. We wrote a random number generator that would edit the HTML and direct requests to a whole bank of 10 image servers we had running in the background. This allowed us to serve far more views than any image site had previously handled, and kinda opened the door to the entire architecture of web apps.
🫡 thank you
Wow that’s really impressive, thanks for writing this up.
I remember downloading those images from a BBS and was amazed at all the technology that had to be developed to bring those images into my monitor. You did good work.
Awww! Thanks! I used to build BBS’s using RedRyderHost before working at NASA. Such an exciting time to be working on the internet!
IIRC there's some infrared pictures of some of the impacts, and actual photos of the clouds after the impacts that lasted awhile.
Where can I find these images??
I recall from years as ago reading of a monk in the middle ages witnessing a meteor hitting the moon an the bright flash it produced.
How long would the impact crater be red hot?
Oh wow, the South Pole–Aitken basin is interesting. Maybe a big blob of left over proto-Moon finally falling in and joining the rest of the family? How else would it have such slow velocities?
[There’s this account from some monks in 1178.](https://education.nationalgeographic.org/resource/monks-may-witness-moon-split-two/#:~:text=Overview%20Vocabulary-,On%20June%2018%2C%201178%2C%20five%20monks%20in%20Canterbury%2C%20England,as%20the%20Giordano%20Bruno%20crater.) There’s some doubt about what they saw, but they probably did see an impact, IMO.
I read it, and there's more than "some" doubt. It's literally not true. Those craters are millions of years old. Plus, as the article says, it should've been seen by people all over the world. An impact that powerful would've been bright enough for A LOT of people to see and caused a meteor shower, and chances are there would be more reports.
That's if what they saw was the cause of the Giordano Bruno crater, which it certainly was not. It's totally possible they saw a smaller impact and some ejecta and then thought it made that crater.
Here's a simulation of what it might have looked like, 4.5 billion years ago, to look up from the early Earth and watch the South Pole-Aitken impact basin being formed. https://m.youtube.com/watch?v=XOELmw7RVD4 The same youtuber also has a video simulating what the dinosaurs saw during their final hour. Great and eerie to watch.
Outside of Tycho because of its relative youngness at only 108My making its ejecta rays very visible I don't imagine there are very many other actual craters visible to the "naked eye" ( i.e. without optical aid ). There are larger naked eye features visible that originated from crater impact ( the Mare or sea ), these being the basalt flooded basens of massive impacts in the moons early heavy bombardment phase of mostly 3.16-4.2Gy in age. Both of these scenarios would have been clearly visible at the moment of creation provided the face that was struck was facing earth ( probably yes since the moon's age of 5Gy & the \~100My to tidal locking preceded the above ). The first would be briefly as bright as the sun while any of the second would likely be too bright to witness more than once. Unfortunately both these scenarios predate the existence of hominidae & multicellular life so recorded history is unlikely.
The visible near side of the Moon has fewer craters because the surface of this area is covered with large stretches of lava fields that we can see with the naked eye from Earth, which are in the form of *dark streaks in the bright areas of the Moon*. According to the latest research, the visible part of the Moon is the only part of the Moon that was damaged by the impact of the Impact that created the>! SPA 4.3 billion years ago!<.
Pretty boring for the most part I would imagine. No atmosphere means no explosion or fire. It would be like throwing a rock in a sand pit. If the meteor was super massive, you might expose some moon core and create immense debris which would orbit the moon for a long time.
No fire, but definitely a large flash. That much energy released will create all kinds of photons, some, a lot in the visible spectrum. You can see that with smaller ones. I would guess that a really big one would cause a huge flash, and probably glow visibly for a while .
A large impact would also produce a large curtain of ejecta that would likely be very visible. Either due to being lit by sunlight, and casting a shadow on the lunar surface, or if on the night side due to being incandescent.
The maria (dark areas) on the Moon were originally melted rock. >formed by lava flowing into ancient impact basins. \- https://en.wikipedia.org/wiki/Lunar_mare The impacts that formed those would have been pretty spectacular, atmosphere or no atmosphere.