# Closesness of our Moon **URL:** \ **Category:** Factual Questions\ **Created:** [August 1, 2019, 3:40pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006 "2019-08-01T15:40:32Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![SuntanLotion](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/suntanlotion/32/16165_2.png) [@SuntanLotion](https://boards.straightdope.com/u/SuntanLotion)\ **Post date:** [August 1, 2019, 3:40pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/1 "2019-08-01T15:40:32Z")
Just read this great book called Bad Astronomy, a chapter of which deals with eclipses. The author says its a coincidence of time that the moon and sun look the same size from Earth. he says the moon is receding. So in the distant past, how close was the moon? there had to be a limit, otherwise it would’ve just crashed into us. ---
**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:** [August 1, 2019, 3:50pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/2 "2019-08-01T15:50:23Z")
It did crash into us. Or rather, Theia crashed into Earth and the ejected debris formed the moon. At the moment of its formation, it was right here. I guess a better formulation of the question is, when moon mostly coalesced into one body, how far away was it? ---
**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:** [August 1, 2019, 3:50pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/3 "2019-08-01T15:50:59Z")
[http://content.time.com/time/specials/packages/article/0,28804,1929328\_1929325\_1929310,00.html](http://content.time.com/time/specials/packages/article/0,28804,1929328_1929325_1929310,00.html) > [@](#): > > Right now the moon is more than 238,000 miles from Earth, but when it formed, it was just 14,000 miles away. [http://curious.astro.cornell.edu/our-solar-system/37-our-solar-system/the-moon/the-moon-and-the-earth/31-how-close-was-the-moon-to-the-earth-when-it-formed-intermediate](http://curious.astro.cornell.edu/our-solar-system/37-our-solar-system/the-moon/the-moon-and-the-earth/31-how-close-was-the-moon-to-the-earth-when-it-formed-intermediate) > [@](#): > > It is not easy to estimate how far away from the Earth the Moon was when it formed, but simulations suggest is was about 3-5 times the radius of the Earth, or about 20 to 30 thousand kilometers [12,500 to 18,600 miles - JL.A.]. (The Moon is currently about 384,000 km or 60 Earth radii away from Earth, which is about fifteen times further away than it was when it first formed.) The Moon probably couldn’t have formed closer than 3 Earth radii because tidal forces from the Earth would just pull it apart again, and it is unlikely that the impact could have ejected material further than 5 Earth radii. It’s not a totally easy questions to answer though as it depends a lot on the (unknown) details of the impact and how the hot material behaved in space. ---
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [August 1, 2019, 3:56pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/4 "2019-08-01T15:56:30Z")
**The Bad Astronomer** used to be active here on this board, many years ago. Here, for example, is one thread in which he participated, that’s at least slightly related to the topic of this one: [How close could the moon get to the Earth…](http://boards.straightdope.com/sdmb/showthread.php?t=117028) ---
**Author:** ![SuntanLotion](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/suntanlotion/32/16165_2.png) [@SuntanLotion](https://boards.straightdope.com/u/SuntanLotion)\ **Post date:** [August 1, 2019, 3:57pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/5 "2019-08-01T15:57:48Z")
looks like I should’ve put this in general Questions, thanks! ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [August 1, 2019, 4:02pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/6 "2019-08-01T16:02:47Z")
> [@Thudlow\_Boink](#): > > **The Bad Astronomer** used to be active here on this board, many years ago. Here, for example, is one thread in which he participated, that’s at least slightly related to the topic of this one: > [How close could the moon get to the Earth…](http://boards.straightdope.com/sdmb/showthread.php?t=117028) FYI… **The Bad Astronomer** = Dr. Phil Plait, the author of “Bad Astronomy”, which is a terrific read about interesting astronomical topics. ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [August 1, 2019, 5:25pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/7 "2019-08-01T17:25:39Z")
Wow, he hasn’t been active here since 2004?!? ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [August 1, 2019, 6:39pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/8 "2019-08-01T18:39:47Z")
He’s busy filming snippets of commentary on random astronomical programs on Science Channel. I see him on there all the time! ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [August 1, 2019, 8:35pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/9 "2019-08-01T20:35:08Z")
I just saw him earlier this week on the PBS series _The Planets_. I had to explain to **Mrs. FtG** that I “know” this guy. Fun fact: he was an advisor for the film _Arrival_. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 2, 2019, 12:55am UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/10 "2019-08-02T00:55:28Z")
**Moderator Action** > [@SuntanLotion](#): > > looks like I should’ve put this in general Questions, thanks! I can fix that. Moving thread from IMHO to GQ. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [August 2, 2019, 4:41am UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/11 "2019-08-02T04:41:22Z")
Phil also has a [blog](https://www.syfy.com/tags/bad-astronomy), which he updates frequently. Usually worth reading. ---
**Author:** ![Walken\_After\_Midnight](https://avatars.discourse-cdn.com/v4/letter/w/b487fb/32.png) [@Walken\_After\_Midnight](https://boards.straightdope.com/u/Walken_After_Midnight)\ **Post date:** [August 2, 2019, 8:33pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/12 "2019-08-02T20:33:59Z")
Incidentally, there was a [pictofact this week on _Cracked_](https://s3.crackedcdn.com/phpimages/pictofact/2/9/8/704298_v2.jpg) about how all the planets in our Solar System could fit between the distance from the Earth to the Moon. ---
**Author:** ![mandala](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mandala/32/95_2.png) [@mandala](https://boards.straightdope.com/u/mandala)\ **Post date:** [August 2, 2019, 11:16pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/13 "2019-08-02T23:16:23Z")
Imagine the red-hot moon looming over the horizon at just 14,000 miles! :eek: It would give me a heart attack. Good thing no life existed back then. As it is, the moon appears disconcertingly large near the horizon even at its current distance. I wish this illusion did not exist. Somehow the Sun being the same angular size at the horizon does not bother me. One sorta expects the Sun to be large. ---
**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:** [August 3, 2019, 12:39am UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/14 "2019-08-03T00:39:40Z")
The numbers might be good, but that pictofact shows Saturn as bigger than Jupiter. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [August 3, 2019, 2:30am UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/15 "2019-08-03T02:30:28Z")
> [@mandala](#): > > Imagine the red-hot moon looming over the horizon at just 14,000 miles! :eek: It would give me a heart attack. Good thing no life existed back then. As it is, the moon appears disconcertingly large near the horizon even at its current distance. I wish this illusion did not exist. Somehow the Sun being the same angular size at the horizon does not bother me. One sorta expects the Sun to be large. It’s kind of the other way around. The Moon, being smaller than Earth, cooled down enough to form its crust while the Earth was still a 7,000 degree ball of magma. In fact, one of the theories for why the near side has a thinner crust than the far side is that the heat from the Earth may have blasted lunar crust from the near side and deposited it on the far side. This could have been responsible for the volcanism that created the near side maria. All that said, there are still many competing theories for how the Moon and Earth were created and how all the features we see today came to be. They all start with a collision between the Earth and a Mars-sized planet, but differ in the details over what happened next. ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [August 3, 2019, 3:22pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/16 "2019-08-03T15:22:47Z")
> [@Sam\_Stone](#): > > It’s kind of the other way around. The Moon, being smaller than Earth, cooled down enough to form its crust while the Earth was still a 7,000 degree ball of magma. > > In fact, one of the theories for why the near side has a thinner crust than the far side is that the heat from the Earth may have blasted lunar crust from the near side and deposited it on the far side. This could have been responsible for the volcanism that created the near side maria. > > All that said, there are still many competing theories for how the Moon and Earth were created and how all the features we see today came to be. They all start with a collision between the Earth and a Mars-sized planet, but differ in the details over what happened next. Was the moon already tidally locked when this process was happening? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [August 3, 2019, 5:33pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/17 "2019-08-03T17:33:00Z")
> [@USCDiver](#): > > Was the moon already tidally locked when this process was happening? A previous [thread](https://boards.straightdope.com/sdmb/showthread.php?t=544727) on when the Moon became tidally locked. This and other similar topics around the Net all suggest it was within a few million years. Maybe 16-20 million if not sooner. So it was still quite close with all the effects implied by that. ---
**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:** [August 3, 2019, 7:30pm UTC](https://boards.straightdope.com/t/closesness-of-our-moon/838006/18 "2019-08-03T19:30:32Z")
On a related note, [recent research](https://www.space.com/moon-older-than-thought-apollo-lunar-rocks.html) suggests that the moon is older than we thought.