Is the Moon really upside down in Australia?

Compared with the view from Europe or North America, yes — rotated by roughly 180°, because observers in the two hemispheres stand head-to-foot relative to each other. Locally, of course, nothing looks wrong: the southern view is exactly as correct as the northern one.

Which side is lit when the moon is waxing?

In the northern hemisphere, the right side; in the southern, the left. Near the equator the terminator runs almost horizontally, and the crescent can look like a boat or a smile.

Why does the crescent sometimes lie on its back?

The crescent always points toward the Sun below the horizon. Near the tropics, at dusk or dawn, that direction can be almost straight down — so the crescent lies horizontally, the “wet moon” of Pacific folklore.

Guides

Why the Moon looks upside down in the southern hemisphere

Travellers notice it before they can explain it: from Sydney, the Moon of the postcards hangs the wrong way up. Nothing happened to the Moon — something happened to you.

Your “up” is not my “up”

The Moon always turns the same face toward Earth. But “up” on that face is decided by the observer: your head points away from the centre of the Earth, and an observer in Buenos Aires points the opposite way from one in Paris. Two people looking at the same Moon from the two hemispheres therefore see the same face rotated — at the equator-to-pole extreme, a full 180°. The rabbit some cultures see in the northern moon becomes, quite naturally, a different figure in the south.

The same logic reverses the growth rule of thumb: in the north the waxing moon is lit on the right; in the south, on the left. A crescent that means “growing” in Lisbon means “shrinking” in Cape Town.

The crescent also tilts through the night

Subtler: the crescent's angle changes hour by hour even from one spot, as the sky rotates overhead — astronomers call the correction the parallactic angle. And near the tropics the crescent can lie almost flat on its back, like a smile: the “wet moon” of Hawaiian folklore, a boat in other traditions. None of this is an optical illusion; it is plain spherical geometry, and it is computable to the degree.

What an honest moon app should do

Most apps draw the Moon as seen from the northern mid-latitudes, wherever you actually are. Plenilune computes the apparent orientation for your position and hour — the engraved disc leans as the real Moon does in your sky, in Melbourne as in Montreal. It is the kind of exactness you only notice when it is missing.

Questions

Is the Moon really upside down in Australia?: Compared with the view from Europe or North America, yes — rotated by roughly 180°, because observers in the two hemispheres stand head-to-foot relative to each other. Locally, of course, nothing looks wrong: the southern view is exactly as correct as the northern one.
Which side is lit when the moon is waxing?: In the northern hemisphere, the right side; in the southern, the left. Near the equator the terminator runs almost horizontally, and the crescent can look like a boat or a smile.
Why does the crescent sometimes lie on its back?: The crescent always points toward the Sun below the horizon. Near the tropics, at dusk or dawn, that direction can be almost straight down — so the crescent lies horizontally, the “wet moon” of Pacific folklore.

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