On Friday, January 21, 2022 at 9:58:57 AM UTC-5, James Nicoll wrote:
> In article <
b981bcab-178f-457e...@googlegroups.com>,
>
pete...@gmail.com <
pete...@gmail.com> wrote:
> >On Thursday, January 20, 2022 at 11:14:33 PM UTC-5, Jay E. Morris wrote:
> >> On 1/18/2022 8:14 AM, James Nicoll wrote:
> >> > Empty Earths: Five SF Stories Set on a Depopulated Planet
> >> >
> >
https://www.tor.com/2022/01/18/empty-earths-five-sf-stories-set-on-a-depopulated-planet/
> >> Don't know why but it irks me when that picture is rotated. Guess it's
> >> the terminator line running east-west.
> >
> >The title bothers me, not the terminator. At any given point on the Moon's
> >surface, the Earth, if visible at all, is at a fixed point in the sky,
> >neither rising nor setting.
> Not quite. There's libration (the moon wobbles a little bit) so judicious
> choice of location would permit a Loonie to watch the Earth rise and set.
> Only about 1/5th of the surface sees Earthrise/set, and it is very very
> slow: two days for the Earth to move its own diameter in the sky.
It long ago occurred to me that on the earth-facing side of the Moon,
the planet's direction and orientation in the sky would be a great landmark for
finding your way around. Facing it points you at the center of the
Earth facing side, it's altitude in the sky tells you how far away that point
is (modulo libration, as you point out), and orientation the north/south
pole line tells you on which radial line to that point you are.
Libration is less than 8 degrees EW, and less than 7 NW, which would
add up over long distances.
Can you recall any stories where this was a feature?
pt