When I’m in San Diego, I’m used to the bright side off the moon being on the right side when waxing and on the left side when waning. However, the moon right now is definitely waxing and yet it is leaning left. Last night it was a half moon, with the line between light and dark running from a position of about 10 o’clock to 4 o’clock (the bright side being the bottom left).
At first I figured it’s because I’m currently in the tropics, so the Tropic of Cancer is north of me, whereas I’m used to it being south. However, given that it’s February, the moon should be hovering somewhere south of the equator, so I’m not clear why it should seem flipped.
Statements about orientation of the moon are useless without statements about orientation of the observer. When you look at the moon in your description, in which direction are you facing?
Fear Itself: tonight it looks almost exactly like that, except backwards.
DSYoungEsq: I’m in Ho Chi Minh City, 10 degrees 45 N, 106 degrees 40 E. When I’m looking at the moon, I’m facing the moon. I believe it’s closer to rising than setting, so I would say it’s east. However, if not, is that what would make the difference?
If you face away from the moon, then bend over and view it from between your legs, it will look like that. Otherwise, I see nothing in the current moon data to explain your observation.
I’m no scientist, so bear with me as I try to sort this out for myself.
Imagine a waxing half moon for purposes of this exercise.
If you are standing at the North Pole, the right side appears lit and the left is dark. At the South Pole, flip yourself upside down, and the left appears lit and the right is dark.
At the equator, assuming for the moment that the moon is on our equator, when the moon is setting, the bottom half appears lit and the top half is dark. At the equator, when the moon is rising, the top half appears lit and the bottom half appears dark.
If you are just north of the equator, where you are, when the moon is rising, the dividing line might appear to go from 10:00 to 4:00 on the moon face, with the bright part being the “upper right side.” When the moon sets, that dividing line will appear to run from 2:00 to 8:00 on the moon face, with the bright part being the “lower right side.” When the moon hits its apex in the sky, that dividing line will appear to run from 12:00 to 6:00 on the face of the moon, with the bright part being on the right side.
If you are just south of the equator, it should be pretty much the opposite.
So, it seems to me the only way to have a waxing moon lit on the left side is to be south of the equator (or “south of the moon” since the moon isn’t on really on our equator). Did they move Viet Nam without telling me? Otherwise, the moon is now “north” of the equator and “north” of you.
Thank you for that. Now that I looked up ecliptic on Wiki, I guess everyone south of 23°26’ N latitude will see this “backwards” moon at some point, as described in the OP. People in San Diego, at about 33° N, won’t
Again, I know very little of astronomy so feel free to beat me down if I am wrong.
As the earth rotates on its axis during the day, Viet Nam will swing below the ecliptic for a little less than half the day. San Diego will not cross the ecliptic.
To better understand more precisely what you saw, since it is now winter, the sun would be off to the far left side of that picture. Point your ass at your monitor; that is the moon. Imagine Viet Nam has rotated on the Earth’s axis and is now toward the right side of the planet on that picture, below the ecliptic.
At that point, if someone in that picture in Viet Nam could look out of your monitor and see your ass, they would experience the “backwards waxing half moon” you saw.
Are you viewing it well after midnight? Deep into the morning hours? If so, then the moon appears to “turn” as it moves across the sky. If you’re used to seeing the moon in the evening, rather than the morning, it’ll look like it’s upside down.
If you draw an imaginary line from the two horns of the terminator… then imagine a perpendicular line running straight off of that, it should point directly at the sun.
The orientation of the crescent evening moon changes with the months, as the ecliptic makes different angles with the horizon. Sometimes it is almost 90 degrees for me (30 N latitude), and the moon is in what I call a “Cheshire Cat” mode, which it was last week.
The orbit of the moon is tilted about 5 degrees from the ecliptic, so the latitude where it’s possible to see the moon inverted is about 27.5 degrees N. But it’s going to be quite rare to see this when you get close to that latitude.
Whatever would lead you to that conclusion? The moon circles the ecliptic every month, not every year.
In February, the new moon aligns with the Sun in the southern sky. From a few days past new moon to a few days past full, it moves to the north. Hence, a half moon in February is in the northern sky, and from Vietnam, you’re looking at it from the south. Thus the flip.
What I meant was, when you face the moon, are you facing a southerly direction, or a northerly direction. The answer to your question will determine which “side” the moon is lit on.
Today I watched the moon set here in NW Ohio. It set several degrees north of due West. So I can imagine that, south of here by quite a bit, it could well be north of the line running from due East to due West across the sky.
What I meant was, when you face the moon, are you facing a southerly direction, or a northerly direction. The answer to your question will determine which “side” the moon is lit on.
Today I watched the moon set here in NW Ohio. It set several degrees north of due West. So I can imagine that, south of here by quite a bit, it could well be north of the line running from due East to due West across the sky for much of the night.
