# Everyone knows that the moon has craters, right? But when was the last one recorded? **URL:** \ **Category:** Factual Questions\ **Created:** [April 11, 2021, 5:42pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807 "2021-04-11T17:42:29Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [April 11, 2021, 9:28pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/21 "2021-04-11T21:28:55Z")
There was an [event](https://www.wired.com/2008/06/june-18-1178-english-monks-observe-lunar-explosion/) in 1178 that might have been a lunar impact bright enough to be seen with the naked eye. (On the other hand, an impact that big should have thrown up enough ejecta to create noticeable meteor showers on Earth, of which there are no accounts.) ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 11, 2021, 9:34pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/22 "2021-04-11T21:34:20Z")
> [@Bullitt](#): > > Well, _ **that’s** _ reassuring! The biggest crater the Earth has had in 50,000 years is less than one mile across. > **[Meteor Crater](https://en.wikipedia.org/wiki/Meteor_Crater)** > > Meteor Crater or Barringer Crater is an impact crater about 37 mi (60 km) east of Flagstaff and 18 mi (29 km) west of Winslow in the desert of northern Arizona, United States. The site had several earlier names, and fragments of the meteorite are officially called the Canyon Diablo Meteorite, after the adjacent Canyon Diablo. > Meteor Crater lies at an elevation of 5,640 ft (1,719 m) above sea level. It is about 3,900 ft (1,200 m) in diameter, some 560 ft (170 m) deep, and is surrounded by a rim... Strikes that size were much more common in the very early solar system than they are today. (Except after major collisions in the asteroid belt, such as the one around 470 million years ago): > **[A Distant Asteroid Collision Gave Earthly Biodiversity An Ancient Boost](https://www.universetoday.com/143450/a-distant-asteroid-collision-gave-earthly-biodiversity-an-ancient-boost/)** > > A new study shows that extreme amounts of dust from an asteroid collision cooled the Earth over 460 mya, and led to much greater biodiversity. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [April 12, 2021, 12:50am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/23 "2021-04-12T00:50:01Z")
> [@Bullitt](#): > > the moon has clearly shielded us from some impacts … But the earth with more gravity is a bigger ‘meteor magnet’ than the moon is — if I can use that term and I hope you understand its meaning. I, for one, understand you clearly. By definition, the craters on the near side of the moon are the result of meteors that passed the earth and then hit the moon. Similarly, the craters on the _far_ side of the moon are the result of meteors coming in the other direction: they hit the moon before reaching the earth. If all the meteors in the universe are moving in random directions, then about half of them would be coming from a direction where the moon is closer, and about half would be coming from a direction where the earth is closer. But here’s the big gotcha: Of all the meteors which start out on the earth side, a lot of them are not going to reach the moon. First of all, the earth is an obstacle (though not nearly as large as many people would imagine), which will simply block many of the meteors that are heading to the moon. But much more importantly, the earth’s gravity is so much stronger than the moon’s that it will be much more likely to knock the meteors off course. Some of those meteors will be captured by the earth’s gravity and crash on earth, and others will simply go off course. In contrast, of the meteors coming from the other direction, relatively few will go off course because of the earth’s gravity, and a great many will crash into the moon. To me, the above explains why the far side of the moon is rather uniform and is totally covered with random craters, whereas the near side - which has been protected by the earth to some degree - still retains the gigantic “seas” of so long ago. There have simply been fewer meteors hitting the near side to ruin the scenery. Surely someone smarter than me has either confirmed or debunked this idea. Anyone know? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 12, 2021, 12:58am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/24 "2021-04-12T00:58:07Z")
> [@Keeve](#): > > Surely someone smarter than me has either confirmed or debunked this idea. Anyone know? Read the “differences” section on the “far side of the moon” Wikipedia page linked up-thread. (Also, being pedantic): > **[What’s the Difference Between a Meteoroid, a Meteor, and a Meteorite?](https://www.britannica.com/story/whats-the-difference-between-a-meteoroid-a-meteor-and-a-meteorite)** > > The difference between the three depends on where they are. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [April 12, 2021, 1:05am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/25 "2021-04-12T01:05:25Z")
> [@Darren\_Garrison](#): > > Read the “differences” section on the “far side of the moon” Wikipedia page linked up-thread. Yes, I see what you mean (in the 3rd paragraph there). I’m a little disappointed that it uses the words “obscure” and “shield” (which connote a physical barrier) and doesn’t mention anything about gravitational effects. But I concede that they know more about it than I’ll ever hope to. Ignorance fought. Thank you. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [April 12, 2021, 2:08am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/26 "2021-04-12T02:08:26Z")
> [@Darren\_Garrison](#): > > > [@Bullitt](#): > > > > Well, _ **that’s** _ reassuring! > > The biggest crater the Earth has had in 50,000 years is less than one mile across. > > [Meteor Crater - Wikipedia](https://en.wikipedia.org/wiki/Meteor_Crater) > > Strikes that size were much more common in the very early solar system than they are today. (Except after major collisions in the asteroid belt, such as the one around 470 million years ago): > > [A Distant Asteroid Collision Gave Earthly Biodiversity An Ancient Boost - Universe Today](https://www.universetoday.com/143450/a-distant-asteroid-collision-gave-earthly-biodiversity-an-ancient-boost/) I’ve visited Meteor Crater, in early 2016, and it is a good place to go. The visitors center displays and film are good. They have a piece of the meteorite there, and you can touch it. What’s interesting is that when I knocked on it with my wedding ring, it rang metallically, almost like a bell. Highly recommended, if you’re near Winslow AZ on I-40. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 12, 2021, 2:39am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/27 "2021-04-12T02:39:22Z")
> [@Keeve](#): > > I’m a little disappointed that it uses the words “obscure” and “shield” (which connote a physical barrier) and doesn’t mention anything about gravitational effects. That is because asteroids/meteoroids are travelling so fast and Earth’s gravity is so relatively weak that gravitational effects aren’t that significant. Meteoroids that hit Earth aren’t drawn in by gravity–they hit because they are trying to pass through the same space at the same time. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [April 12, 2021, 3:21am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/28 "2021-04-12T03:21:18Z")
The area of the moon as seen from Earth is 0.2 square degrees. The area of the whole sky is 41,253 square degrees. The ratio is about 1 to 200,000. So ignoring gravitational effects, which as mentioned are small, the chance of a meteoroid heading for Earth coming from a random direction being blocked by the moon is about 1 in 200,000. However this underestimates the probability since a meteor is more likely to approach near the ecliptic than randomly across the sky. On the other other hand, the Moon is always near the ecliptic too. ---
**Author:** ![pirviii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pirviii/32/3233_2.png) [@pirviii](https://boards.straightdope.com/u/pirviii)\ **Post date:** [April 12, 2021, 3:26am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/29 "2021-04-12T03:26:21Z")
I took the family there when we were visiting my brother when he lived in Flagstaff. I preferred checking out the casinos along I40 in New Mexico. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [April 12, 2021, 4:09am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/30 "2021-04-12T04:09:45Z")
> [@Peter\_Morris](#): > > I think that ‘dark side’ is a fair description. It’s like that Victorian-era phrase, “darkest Africa.” They didn’t mean it was really shady under all those trees in the jungle nor that the locals had extra melanin but that it was unknown – from the European point of view. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [April 12, 2021, 4:19am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/31 "2021-04-12T04:19:49Z")
Oh, and doing a quick google-search, 300-km across is about the smallest crater that can be distinguished by the naked eye. That’s a pretty big thump. [Cite](https://my-moon.org/wp-content/uploads/2016/05/MOON_FAQ_website-1.pdf). > The smallest features we can observe on the moon with the naked eye are generally greater than 300km across. A great example of a small but still visible object on the moon is the brilliant crater Tycho on the south of the moon. ---
**Author:** ![74westy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/74westy/32/3950_2.png) [@74westy](https://boards.straightdope.com/u/74westy)\ **Post date:** [April 12, 2021, 4:38pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/32 "2021-04-12T16:38:06Z")
> [@Northern\_Piper](#): > > There is no dark side of the moon Matter of fact, it’s all dark. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [April 12, 2021, 5:00pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/33 "2021-04-12T17:00:10Z")
> [@pirviii](#): > > I took the family there when we were visiting my brother when he lived in Flagstaff. I preferred checking out the casinos along I40 in New Mexico. That’s fine. To each their own. I’d only stop at a casino to use their bathroom. And even that I would avoid, because they force you to walk deep into the pits of the casino just to get to the bathroom. That, and also the cigarette smoke. No casinos for me, except on the rare occasions I want to play. Meteor Crater’s visitors center is a nice diversion in that part of the country. I’d also like to visit The Eye of Quebec, Lake Manicouagan. It’s massive. At 750 sq miles it’s much larger than MCAZ. MCAZ is less than 1 sq mile. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [April 12, 2021, 5:16pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/34 "2021-04-12T17:16:55Z")
> [@Bullitt](#): > > I’ve visited Meteor Crater, in early 2016, and it is a good place to go. It’s amazing how close the crater is to the visitor’s center. Talk about a near miss! 😛 ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 12, 2021, 6:51pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/35 "2021-04-12T18:51:29Z")
> [@Bullitt](#): > > I’d also like to visit The Eye of Quebec, Lake Manicouagan. It’s massive. But only the fifth largest known impact site remaining on Earth. > **[Asteroid Day: 5 Biggest Known Impact Craters on Earth Caused By Asteroid...](https://weather.com/en-IN/india/science/news/2020-06-30-asteroid-day-5-biggest-impact-craters-on-earth-caused-collisions)** > > While several asteroids continue to pass-by Earth on a regular basis, our planet hasn’t always been sneaky enough to dodge all of them. Some rocks have collided with Earth head-on on multiple occasions, forming large impact craters that are visible... ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 12, 2021, 6:55pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/36 "2021-04-12T18:55:28Z")
And also in the US is the Chesapeake Bay crater: > **[Chesapeake Bay impact crater](https://en.wikipedia.org/wiki/Chesapeake_Bay_impact_crater)** > > Pages for logged out editors learn more > > The Chesapeake Bay impact crater is a buried impact crater, located beneath the mouth of Chesapeake Bay, United States. It was formed by a bolide that struck the eastern shore of North America about 35.5 ± 0.3 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" impact craters in the world. > Continued slumping of sediments over the rubble of the crater has helped shape the Chesapeake Bay. > During the warm late ... ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 12, 2021, 7:56pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/37 "2021-04-12T19:56:03Z")
> [@Keeve](#): > > But much more importantly, the earth’s gravity is so much stronger than the moon’s that it will be much more likely to knock the meteors off course. Some of those meteors will be captured by the earth’s gravity and crash on earth, and others will simply go off course. In contrast, of the meteors coming from the other direction, relatively few will go off course because of the earth’s gravity, and a great many will crash into the moon. I know you’ve already learned this isn’t quite right, but here’s another factor. Ref this: > [@Darren\_Garrison](#): > > That is because asteroids/meteoroids are travelling so fast and Earth’s gravity is so relatively weak that gravitational effects aren’t that significant. Meteoroids that hit Earth aren’t drawn in by gravity–they hit because they are trying to pass through the same space at the same time. As **Darren** says, Earth’s gravity bends the path of income asteroids a smidgen. But it is just as likely to convert what would, absent Earth, be a near miss into a hit as it is to convert what would, absent Earth, be a hit into a near miss. For an simpler example, imagine shooting a gun towards a target with no wind. But you’re a crappy shot with shaky hands and sometimes your aim is a little left, sometimes a little right, and sometimes on the money. So some shots hit and some go to either side. Now let’s crank up a big wind from the left and do the same shooting. Some that would have gone by to the left now hit the target and some that would have hit the target now miss on the right side. No net difference. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [April 12, 2021, 8:03pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/38 "2021-04-12T20:03:23Z")
> [@LSLGuy](#): > > just as likely to convert what would, absent Earth, be a near miss into a hit Yes, truly. I’m very surprised that I didn’t think of that. Thanks! ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 12, 2021, 8:20pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/39 "2021-04-12T20:20:43Z")
Right, so even what gravitational effects there are still (mostly) cancel out (not completely, but it’s a good approximation). Roughly speaking, the amount of shielding the Moon provides for the Earth is the Moon’s size in the sky compared to the size of the whole sky (or vice-versa, for the shielding Earth provides to the Moon). And while the Earth takes up a larger portion of the lunar sky than the Moon does in our sky, it’s still not very much. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 12, 2021, 8:44pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/40 "2021-04-12T20:44:45Z")
Gravity falls with the inverse square of distance, so an object just a million km out (practically nothing on the scale of the solar system) feels just a 0.0004 meter per second tug from Earth: > **[Online calculator: Acceleration of gravity](https://planetcalc.com/1758/)** > > Acceleration of gravity calculation on the surface of a planet. It's possible to calculate the acceleration above the surface by setting the sea level. But it won't be possible under the surface - this is a wrong formula. [Previous page](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807.md?page=1) [Next page](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807.md?page=3)