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Later this month and into February, six of our solar system's eight planets will snap to attention and march in something like a long, bent line — or two separate line segments, anyway — from east to west across the early evening sky. While they'll be doing that for many weeks, Jan. 21 marks the peak of what's called a planetary alignment, which simply means a bunch of planets assembling in the same section of sky.
They may look like they're arranged in tight formation. But remember, that's a grand illusion. The planets' orbits around the sun are concentric ovals of cosmically different sizes, so any planets that appear side-by-side to us are actually separated by millions, or even billions, of miles of deep space.
It's like seeing two or more traffic lights ahead of you on the same road. The lights may appear very few degrees apart to your eye, but your perspective-practiced brain can tell that the first one is mere yards away while the next is hundreds of yards farther away, and so on into the distance.
When just two heavenly bodies appear to pull close together in the sky, it's called a conjunction. When a whole gaggle of planets manage the trick, that's planetary alignment — informally known as a planet parade.
This winter's parade is going to be a doozy, said Jim Todd, the director of space science education at the Oregon Museum of Science and Industry. Sharing the evening sky this winter will be six planets. Not all of these cosmically distant bodies can be seen without binoculars, if not a telescope, but some can.
Start by scanning the southern sky right after sunset (at 5:02 p.m. Jan. 21), which is when planets already in the sky — but hidden by sunlight — will start to emerge.
Leading the way in the southwest will be brilliant Venus. Venus never appears very far from the sun, whether rising or setting, since it is closer to the sun than we are. (Earth's average distance from the sun is 91 million miles; Venus' average distance is 67 million miles.) Because of that proximity, and because it's thickly blanketed by reflective cloud cover, Venus tends to be the most attention-grabbing planet up there. That's why it's nicknamed both "morning star" and "evening star."