On Sep/26/2020 at 23:01, David Spain wrote :
Thank you for forwarding the story about "Can the Moon be upside down?"
I had never given much thought to what the moon looks like in the
southern hemisphere since I haven't been south of the equator. I need to
get out more!

Dave


I would like to add that in my opinion, the most striking difference
that can be seen in the appearance of the moon is not, as the planetary
society article seems to imply, the difference between the full moon
seen from the north pole compared to the full moon seen from the south
pole. Yes, the craters aren't in the same orientation, but most people
hardly notice the craters on the moon.

On the other hand, if at a the equator on an equinox, you look at a half
moon as it rises or sets near the horizon. The half of the moon that is
lit is the half facing the sun. A half moon rises or sets at midnight
(the waning half moon rises at midnight, the waxing half moon sets at
midnight). So when you see the half moon rising or setting, the sun is
straight below your feet and the half of the moon that is lit up, is the
half of the moon near the ground and the terminator is horizontal.

If at the same time someone at the pole looks at the half moon, he will
see the terminator 90 degrees from what is seen at the equator. At the
pole, the half moon is shaped like a D (waxing moon at the north pole or
waning moon at the south pole) or like an inverted D, or if you prefer a
closed C (waning moon at the north pole or waxing moon at the south pole).

If you aren't quite at the pole but either north or south of the
tropics, the rising half moon might not have a vertical terminator but
it won't be horizontal. The closer you go to a pole the more upright the
half moon will look.

At the December solstice on the Tropic of Cancer (23.4 deg north) at
midnight, the sun is straight below your feet, and you might see a half
moon rise much the same way it would be seen at the equator on the
equinox. But at the June solstice, at midnight, the sun is not straight
below your feet, it is pointed in a direction straight below the feet of
someone at the Tropic of Capricorn which is a direction nearly 47
degrees from straight below your the feet of the person on the Tropic of
Cancer at midnight. So someone living near the arctic circle going to
the tropic of Cancer at the June solstice might no be amazed to see the
moon at such an angle, it is what he is used to see at the December
solstice. On the other hand if he goes there at the December solstice he
might see the half moon terminator horizontal which is much different
from what he usually sees. At the arctic circle, he sees a terminator
going from completely vertical at the June solstice to slanted 47
degrees at the December solstice.

So for someone living in mid latitudes in the northern hemisphere if you
want to see an unusual moon, you want to go north in June, to see the
moon more upright, or south in December to see the moon more slanted. In
the southern hemisphere you move north in December or south in June.
Just a few thousand kilometres should give a noticeable difference.


Alain Fournier