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Well, the notion that one metal is liquid at our arbitrary reference temperature is a coincidence. But it is no coincidence that the moon's orbital and rotation

Well, the notion that one metal is liquid at our arbitrary reference temperature is a coincidence. But it is no coincidence that the moon's orbital and rotational periods are the same; this is due to a mechanical phenomenon called Tidal Locking[1] and is actually quite common for natural satellites. [1] https://en.wikipedia.org/wiki/Tidal_locking https://en.wikipedia.org/wiki/Tidal_locking (posting as alt because I left noprocrast on!)

keenerd 13y ago
An amazing actual coincidence is that the sun and moon appear almost the same size as each other from the surface. The opportunity for such perfect total solar eclipses (with naked-eye visible Baily's Beads) is not common in the universe. There is at least one short story (the title escapes me) that suggests that our #1 tourist attraction for visiting aliens would be total solar eclipses. edit: Found it, maybe. This does not sound like the one I read. > Illegal Alien, by Robert J. Sawyer (1997). An alien visits Earth, supposedly for "research purposes", and observes a total solar eclipse. He then speculates that Earth may be the only planet in the entire Universe whose moon covers its sun perfectly (with only transits or occultations occurring on other planets).
- ekianjo 13y ago
  Interesting point - but wouldn't Jupiter or Saturn with their many moons also experience solar eclipses in a similar way ? Maybe not as perfect as on Earth, but certainly some of their moons could obstruct the sun?
  - keenerd 13y ago
    Those are called transits and occlusions. Very dull and quite frequent. And gas giants don't have a fixed surface you can stand on. I guess you could find the optimal distance to hover in your space ship to see an eclipse, assuming it is above the cloud layer. But where is the novelty in that? Plus the sun is much less impressive way out there. Jupiter is 5 times further (Sun appears 0.04 the size). Saturn is 9.5 AU and so the Sun appears 0.011 the size. Eclipses are still not likely just because you have a bunch of moons. Usually moons will orbit on the planet's plane of orbit. The Earth-Moon system (being more of a binary planet relationship) orbits on the solar plane instead of around the Earth's tilted equator, meaning the Sun/Moon/Earth is vastly more likely to be in alignment for an eclipse.
- phaemon 13y ago
  I think my favourite coincidence, are Saturn's moons Epimetheus and Janus. One of them orbits just below the other and they happen to be in such a position, that as they approach each other, the lower one gains momentum from the mutual gravitational attraction, while the higher one loses momentum. So every four (earth) years, they swap orbits! When I first heard about that, I just thought it was awesome :-D
- lmm 13y ago
  Are you thinking of Iain Banks' Transition? (Not a short story though).

keenerd 13y ago

An amazing actual coincidence is that the sun and moon appear almost the same size as each other from the surface. The opportunity for such perfect total solar eclipses (with naked-eye visible Baily's Beads) is not common in the universe. There is at least one short story (the title escapes me) that suggests that our #1 tourist attraction for visiting aliens would be total solar eclipses. edit: Found it, maybe. This does not sound like the one I read. > Illegal Alien, by Robert J. Sawyer (1997). An alien visits Earth, supposedly for "research purposes", and observes a total solar eclipse. He then speculates that Earth may be the only planet in the entire Universe whose moon covers its sun perfectly (with only transits or occultations occurring on other planets).

ekianjo 13y ago
Interesting point - but wouldn't Jupiter or Saturn with their many moons also experience solar eclipses in a similar way ? Maybe not as perfect as on Earth, but certainly some of their moons could obstruct the sun?
- keenerd 13y ago
  Those are called transits and occlusions. Very dull and quite frequent. And gas giants don't have a fixed surface you can stand on. I guess you could find the optimal distance to hover in your space ship to see an eclipse, assuming it is above the cloud layer. But where is the novelty in that? Plus the sun is much less impressive way out there. Jupiter is 5 times further (Sun appears 0.04 the size). Saturn is 9.5 AU and so the Sun appears 0.011 the size. Eclipses are still not likely just because you have a bunch of moons. Usually moons will orbit on the planet's plane of orbit. The Earth-Moon system (being more of a binary planet relationship) orbits on the solar plane instead of around the Earth's tilted equator, meaning the Sun/Moon/Earth is vastly more likely to be in alignment for an eclipse.
phaemon 13y ago
I think my favourite coincidence, are Saturn's moons Epimetheus and Janus. One of them orbits just below the other and they happen to be in such a position, that as they approach each other, the lower one gains momentum from the mutual gravitational attraction, while the higher one loses momentum. So every four (earth) years, they swap orbits! When I first heard about that, I just thought it was awesome :-D
lmm 13y ago
Are you thinking of Iain Banks' Transition? (Not a short story though).