Why Does The Moon Look Upside Down From Australia?

Why does the Moon look upside down from Australia?
The Moon seen from the southern hemisphere, taken on the 25th of November 2012, from Montevideo, Uruguay. Image credit: Fernando da Rosa, CC BY A-SA 3.0

The Moon seen from the southern hemisphere, taken on the 25th of November 2012, from Montevideo, Uruguay. Image credit: Fernando da Rosa, CC BY A-SA 3.0

Originally posted on Forbes!

Those of us who live in the Northern Hemisphere of our planet are used to a very specific view of the Moon, and, if you never travel outside of the Northern Hemisphere, journeying only to Europe, North America, Asia or the Arctic expanses, that view of the Moon would never change by very much.

However, once you move to the Southern Hemisphere, visiting South America, Africa, Australia or New Zealand, something will indeed seem off about the Moon. It’s upside down in the sky, relative to what you’d be used to in the Northern Hemisphere. Likewise, if you’re used to a Southern Hemisphere sky, moving to the Northern Hemisphere will turn the Moon upside down relative to what you’re used to.

Many of the portraits of the Moon are oriented in the way you’d see them from the Northern Hemisphere. There’s nothing fundamental about this orientation relative to the Southern Hemisphere orientation, but we’ve designated North as “up” for long enough that that convention has expanded outwards to the whole solar system. With that convention, it makes sense to display the Moon “right-side up,” with the view from the Northern half of the planet.

Full Moon photograph taken 10-22-2010 from Madison, Alabama, USA. Photographed with a Celestron 9.25 Schmidt-Cassegrain telescope. Image credit: Gregory H. Revera, CC BY A-SA 3.0

Full Moon photograph taken 10-22-2010 from Madison, Alabama, USA. Photographed with a Celestron 9.25 Schmidt-Cassegrain telescope. Image credit: Gregory H. Revera, CC BY A-SA 3.0

Why does the Moon look upside down from Australia? It’s because we’re on a spherical planet. If I stand at the North Pole, with my head “up,” and have a friend stand on the South Pole, with their head “up,” relative to the ground, our two heads are pointed in exactly opposite directions. If we both look at the Moon, then I see a Moon with dark Mare stretching along the “top” of the Moon, and a bright region at the bottom. At the South Pole, to a person whose head is pointed in the other direction, the Mare go along the bottom edge of the Moon, with the brighter region stretching across the top. If I were to move between the North and South poles, I would watch the Moon appear to rotate in the sky, as my perspective of “up” changes with the curvature of the Earth.  If I, on the North Pole, wanted to replicate my South Pole friend’s view onto the sky, I should do a perfect handstand, mimicking manually what the curve of the Earth has done more naturally. Obviously, this method of replicating the South Pole’s view isn’t perfect, because things that are directly overhead on the South Pole are blocked from my view at the North Pole by the bulk of the Earth.

In a less extreme case, someone living at 45 degrees North of the Equator (exactly halfway between the North Pole and the Equator) and someone living at 45 degrees south of the Equator, (halfway between the South Pole and the Equator) both standing on the ground, have their heads both pointed “up” but at 90 degrees relative to each other. Since their North/South separation is still an up/down change, then if the two moongazers could swap places, they’d say the Moon had rotated by about 90 degrees. It’s exactly the same kind of perspective shift on the Moon that my friend and I, at the North and South poles, have when looking outward.

The great hunter Orion hangs above ESO’s Very Large Telescope (VLT), in this stunning, previously unseen, image. As the VLT is in the Southern Hemisphere, Orion is seen here head down, as if plunging towards the Chilean Atacama Desert. Image credit: ESO/Y. Beletsky 

The great hunter Orion hangs above ESO’s Very Large Telescope (VLT), in this stunning, previously unseen, image. As the VLT is in the Southern Hemisphere, Orion is seen here head down, as if plunging towards the Chilean Atacama Desert. Image credit: ESO/Y. Beletsky 

The Moon is probably the most dramatic example of this in the night sky, simply because we know it so well, but it’s not the only object that may appear odd in the Southern sky if you’re used to the Northern view. Constellations do the exact same thing. Some Northern constellations are not visible in the Southern skies, but Orion, one of the brightest and easiest-to-spot constellations in the Northern winter sky, is visible from both hemispheres. And just like the Moon’s change, Orion appears upside down, his head towards the ground instead of the rest of the stars overhead.

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