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Why is Orion lying down? How The Hunter taught me how the sky moves
We learn constellations from diagrams that stay conveniently upright. The real sky has other ideas — as I discovered when Orion returned looking distinctly wonky.
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I thought I knew Orion. Three stars in a row for the Belt, Betelgeuse above, Rigel below: it's one of the constellations I have long been able to identify with the least thought, along with Cassiopeia and the Plough/the Big Dipper.
But one fall evening long ago, when I was learning the night sky, I was looking at three bright stars rising in the east and spent an embarrassingly long time wondering whether they really were Orion's Belt. They were at the wrong angle. The rest of Orion followed them into the sky almost sideways, as though somebody had knocked the Hunter over.
What was happening? Nothing had gone wrong with Orion, of course. The problem was the picture of him in my head. Most constellation diagrams are printed in the orientation that makes them easiest to recognize. The sky makes no such promise. Watch Orion rise this month, and the familiar figure can look decidedly unfamiliar at first. Better still, stay outside long enough, and you can watch his orientation change as he rises on his side and swings into the southern sky upright as the night wears on.
Orion stopped being a picture and became evidence that the sky was doing something I didn't expect to see so easily in such a short time — it was moving, and strangely.
In mid-October, you need to be patient to see Orion, but it's one of the best months to catch it rising on its side. From much of North America, look low toward the east shortly before midnight. Orion rises on its side, with the three Belt stars — Mintaka, Alnilam and Alnitak — rising one by one, preceded by Betelgeuse and Bellatrix, followed by brilliant Rigel.
Don't worry if you can't see the whole constellation immediately. Orion is enormous, and when it's close to the horizon, buildings, trees and atmospheric haze can easily hide parts of it. Waiting another hour can transform the view.
As Orion climbs higher, it appears to turn. The Belt changes angle, and the constellation gradually approaches the orientation many of us recognize from winter evenings. It reaches due south around sunrise, by which time the Belt is sloped, but the four corner stars — Betelgeuse and Bellatrix at the top and Rigel and Saiph at the bottom — form the easily recognizable rectangle enclosing it. Orion looks like Orion.
Orion isn't actually performing a slow roll in space. Earth is rotating beneath us, carrying our viewpoint eastward. Stars therefore appear to rise in the east, arc across the sky and eventually set in the west. It's how the night sky works, but it's an effect that's particularly easy to notice with Orion because its shape is so familiar. Instead of trying to understand celestial motion from a diagram, you can watch it happening.