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.
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?
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…
looks like I should’ve put this in general Questions, thanks!
FYI…The Bad Astronomer = Dr. Phil Plait, the author of “Bad Astronomy”, which is a terrific read about interesting astronomical topics.
Wow, he hasn’t been active here since 2004?!?
He’s busy filming snippets of commentary on random astronomical programs on Science Channel. I see him on there all the time!
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.
Moderator Action
I can fix that.
Moving thread from IMHO to GQ.
Phil also has a blog, which he updates frequently. Usually worth reading.
Incidentally, there was a pictofact this week on Cracked about how all the planets in our Solar System could fit between the distance from the Earth to the Moon.
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.
The numbers might be good, but that pictofact shows Saturn as bigger than Jupiter.
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?
A previous thread 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.
On a related note, recent research suggests that the moon is older than we thought.