In reply to Dave Garnett:
>What I've read suggests that rocky planets having moons as relatively large as ours is pretty unusual.
The fact that we have a moon large enough to stabilise our axis of rotation is one of the reasons that our evolution was possible. So whilst it is unusual for a small rocky planet to have a significant moon, it might not be so unusual for such planets to have the stable conditions needed for complex life to evolve (provided they are in a habitable zone).
The size and distance ratio however is a lucky co-incidence (*or is it) which those of a religious persuasion might attribute to a god. Also, as someone said, the moon used to be much closer and is still getting further away.
*Thinking about this a bit more and in relation to some of the conditions required for complex life to evolve, it might not be such a coincidence. Evolution of complex life needs:
A star which burns consistently in a stable way for billions of years to allow enough time for evolution to happen. (e.g. an average sized main sequence star like our sun)
A planet with a stable orbit around a star at the correct distance for a solvent (e.g. water) to be mostly liquid.
The planet needs to be the right size - big enough to still have a molten core after billions of years to generate a magnetic field which keeps that nasty solar wind at bay - not so big that gravity prevents organisms from moving or growing.
The planet needs to have a stable climate so that mass extinctions are rare to give complex life a chance. A moon of the correct size is very helpful in stabilising the axis of rotation (and therefore seasonal climate), but if it was too small it wouldn't keep us stable and if it was too big, a change of the tide would be catastrophic.
Throw in all those variables and the chances of there being a planet inhabited by complex organisms with a moon of about the right size to display the nearest star's chromosphere might not be that small. I'm just musing of course - I don't really believe in co-incidences, but I don't believe in god either.