More astrophysics

[kengr]

I've just realized that I forgot a point I was going to make in my last post.

Earth has several moons, but Luna isn't one of them.

Yes, really.
Compare the Terra/Luna pair with any other moon & planet in the solar system, and you find a number of *glaring* differences.

First of all the center of mass of the Terra/Luna pair is *outside* of Earth. Not

Comments

[fayanora]

"But you do this with Terra and Luna, and Luna's orbit is always concave with respect to the sun. at the points where it is closer to the sun than Terra, the orbit is flatter, but still concave."

I can't even begin to imagine how that's possible. Luna goes around the Earth, so it should be falling away from the sun at certain points. Again, I can't even begin to imagine how it could possibly be otherwise. What would that even look like? How is that even remotely close to being possible?

"Mars doesn't have such stabilizing factor and its axis has flip-floped a lot over the millennia, making it a lot less suitable for life."

That is the least of Mars's issues. It doesn't have a magnetic field because it's not tectonically active. It also doesn't have enough gravity to maintain an appropriate atmosphere for long enough for life to develop.

I like to think multiple smaller moons the same mass as Luna combined might have similar effects to Luna on their planets.

[kengr]

Like I said, the portions of Luna's orbit that take it closer to the sun that Terra are less curved (but not flat). They still concave with respect to the sun, but they aren't curved as strongly as the parts that are farther from the sun than Terra.

Here's an image that might help.

Consider a circle. That's Terra's orbit. Now consider an ellipse with the same center (*not* one of the focal points of the ellipse, but the center).

so part of the time the ellipse will be outside of Terra's orbit, and part of the time it'll be inside Terra's orbit, but it'll always be concave to the sun.

That'd be something like Luna's orbit if there where only two months in a year.

So instead of two "bulges in" and two "bulges out" there are 12, almost 13 in the course of a year.

[fayanora]

I think I'd have to see that in an actual image. The words just aren't translating properly to images in my brain. This is a common problem for me. I can translate my own thoughts and mental images to words, but often, other people's words don't translate very well into images for me. A huge problem for me with reading fiction is I have to assign real people to play certain characters in the story or else what I picture as the characters will be highly random, ranging anywhere from a perpetually-shifting face to a scribble to an empty space. The Harry Potter movies helped me a lot for the characters that were in both the movies and the books. But even then, the book characters who weren't in the movie remained random. And if I watch a cartoon before reading a book or a fanfic, the characters in my mind appear as that style of cartoon

[kengr]

The "multiple smaller moons" doesn't really work out because they'd have to be fairly big *and* fairly close (too get similar tidal effects). I don't think they orbits would work out long term.

Likewise the tidal effects would mostly neutralize each other.