I'm Writing Fiction about the Moon: Some Basic Questions!

Kelly McDonald wrote in
:

There is no such thing as the "Dark Side of the Moon".

"...in fact it's all dark."
-- Pink Floyd

In article ,
Greg D. Moore \(Strider\) wrote:
Actually if you had a moon tidal locked to a planet that was tidal locked to
its sun, you could have an interesting situation.

Except that such a situation is impossible. The only way it kind of works
is if the moon somehow ended up in the sun-planet L2 position... which is
unstable.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Henry Spencer" wrote in message
...
In article ,
Greg D. Moore \(Strider\) wrote:
Actually if you had a moon tidal locked to a planet that was tidal locked
to
its sun, you could have an interesting situation.

Except that such a situation is impossible. The only way it kind of works
is if the moon somehow ended up in the sun-planet L2 position... which is
unstable.

That was my first thought. Then it occurred to me that the moon might be
like our moon with 2 week days and 2 week nights. In that case, the moon
would not be unusual, but the planet would be. Mercury was thought to be
tidal locked to the sun at one time.

In article ,
Mike Rhino wrote:
Except that such a situation is impossible. The only way it kind of works
is if the moon somehow ended up in the sun-planet L2 position... which is
unstable.

That was my first thought. Then it occurred to me that the moon might be
like our moon with 2 week days and 2 week nights. In that case, the moon
would not be unusual, but the planet would be. Mercury was thought to be
tidal locked to the sun at one time.

Actually, Mercury *is* tide-locked to the Sun -- it's just in an odd 3:2
lock rather than the usual 1:1 lock, due to its elliptical orbit.

Returning to the issue, though, there is nothing special about being
tide-locked to a tide-locked body that would give you the situation the
original poster wanted, where the *moon* has permanent darkness on one
side.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Henry Spencer" wrote in message
...
In article ,
Mike Rhino wrote:
Except that such a situation is impossible. The only way it kind of
works
is if the moon somehow ended up in the sun-planet L2 position... which
is
unstable.

That was my first thought. Then it occurred to me that the moon might be
like our moon with 2 week days and 2 week nights. In that case, the moon
would not be unusual, but the planet would be. Mercury was thought to be
tidal locked to the sun at one time.

Actually, Mercury *is* tide-locked to the Sun -- it's just in an odd 3:2
lock rather than the usual 1:1 lock, due to its elliptical orbit.

Returning to the issue, though, there is nothing special about being
tide-locked to a tide-locked body that would give you the situation the
original poster wanted, where the *moon* has permanent darkness on one
side.
--
It seems to me that a tide-locked body in a dawn dusk polar
orbit could well have a permanantly dark side. It just doesn't
require that the primary be tide-locked.

MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article ,
johnhare wrote:
It seems to me that a tide-locked body in a dawn dusk polar
orbit could well have a permanantly dark side...

Mmm, yes, provided the orbit was sun-synchronous -- precesses once around
the primary per primary orbital period -- which requires a rather exact
match between the orbit characteristics and the primary's equatorial
bulge. I can't see that persisting for very long, however; the exact
match is not very stable.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Henry Spencer" wrote in message
...
In article ,
johnhare wrote:
It seems to me that a tide-locked body in a dawn dusk polar
orbit could well have a permanantly dark side...

Mmm, yes, provided the orbit was sun-synchronous -- precesses once around
the primary per primary orbital period -- which requires a rather exact
match between the orbit characteristics and the primary's equatorial
bulge. I can't see that persisting for very long, however; the exact
match is not very stable.

Suppose that it isn't an exact match so that one day lasts 100 years. It
would still be an interesting place.

In article ,
Mike Rhino wrote:
Mmm, yes, provided the orbit was sun-synchronous -- precesses once around
the primary per primary orbital period -- which requires a rather exact
match between the orbit characteristics and the primary's equatorial
bulge. I can't see that persisting for very long, however; the exact
match is not very stable.

Suppose that it isn't an exact match so that one day lasts 100 years...

It would have to be very close to an exact match to be even that good.
I'd class it as a remarkable and strictly temporary coincidence to have a
day/night cycle of more than a few primary years.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Mike Rhino ) wrote:
: "Henry Spencer" wrote in message
: ...
: In article ,
: johnhare wrote:
: It seems to me that a tide-locked body in a dawn dusk polar
: orbit could well have a permanantly dark side...
:
: Mmm, yes, provided the orbit was sun-synchronous -- precesses once around
: the primary per primary orbital period -- which requires a rather exact
: match between the orbit characteristics and the primary's equatorial
: bulge. I can't see that persisting for very long, however; the exact
: match is not very stable.

: Suppose that it isn't an exact match so that one day lasts 100 years. It
: would still be an interesting place.

How about a case where one of the poles points in the direction of the
orbital plane? IOW, at one point in the orbit the north pole points at the
sun and on the other side of the orbit the south pole points toward the
sun. Unlike the Earth's or Mars' ~25 deg. axis tilt this other is more on
the order of a 90 deg. axis tilt.

Eric

"Eric Chomko" wrote in message
...
Mike Rhino ) wrote:
: "Henry Spencer" wrote in message
: ...
: In article ,
: johnhare wrote:
: It seems to me that a tide-locked body in a dawn dusk polar
: orbit could well have a permanantly dark side...
:
: Mmm, yes, provided the orbit was sun-synchronous -- precesses once
around
: the primary per primary orbital period -- which requires a rather
exact
: match between the orbit characteristics and the primary's equatorial
: bulge. I can't see that persisting for very long, however; the exact
: match is not very stable.

: Suppose that it isn't an exact match so that one day lasts 100 years.
It
: would still be an interesting place.

How about a case where one of the poles points in the direction of the
orbital plane? IOW, at one point in the orbit the north pole points at the
sun and on the other side of the orbit the south pole points toward the
sun. Unlike the Earth's or Mars' ~25 deg. axis tilt this other is more on
the order of a 90 deg. axis tilt.

Uranus comes pretty close with an axis tilt of 97.86 degrees.

http://www.solarviews.com/eng/uranus.htm