Two bright lights will appear to almost touch each other the next couple of evenings. It’s all an illusion, though — they’re separated by almost half a billion miles.

Jupiter and Saturn are the largest and heaviest planets in the solar system. And they’re the fifth and sixth planets from the Sun. At their great distances, it takes them a long time to orbit the Sun: 12 years for Jupiter, and almost 30 years for Saturn. That’s also how long it takes them to circle through the background of stars.

Their combined motion means they meet up once every 20 years. Most meetings aren’t as close as this one, though. The paths of both planets are tilted a bit with respect to the Sun’s path across the sky. So the geometry has to be just right for them to pass as close as they are now.

The planets are in the southwest as darkness begins to fall. Jupiter is the brighter of the two, and is easy to pick out. Saturn will stand just above Jupiter tonight, and almost side by side with it tomorrow night.

Their closest approach actually comes tomorrow morning, when they’ll pass just one-tenth of a degree from each other — the width of a pencil lead held at arm’s length. They won’t be quite that close by the time they pop into view in the early evening, but almost.

After tomorrow, Jupiter and Saturn will pull apart. It’ll be a gradual change, though. They’ll remain close as they drop from sight in the twilight early next year.

Script by Damond Benningfield

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