Stargazers will get a rare planetary triple treat this weekend when Jupiter, Mercury and Mars appear to nestle together in the predawn skies.
About 45 minutes before dawn on Sunday, those three planets will be so close that the average person's thumb can obscure all three from view.
They will be almost as close together on Saturday and Monday, but Sunday they will be within 1 degree of each other in the sky.
Three planets haven't been that close since 1925, said Miami Space Transit Planetarium director Jack Horkheimer.
And it won't happen again until 2053, he said.
"Jupiter will be very bright and it will look like it has two bright lights next to it, and they won't twinkle because they're planets," said Horkheimer, host of the television show Star Gazer. "This is the kind of an event that turns young children into Carl Sagans."
The planets are actually hundreds of millions of miles apart, but the way the planets orbit the sun make it appear they are neighbors in the east-southeastern skies. They'll be visible in most parts of the world.
The experts differ on just how to look at the planets. Horkheimer said naked-eye viewing is fine, but binoculars or a telescope are even better.
But if you use a telescope, be careful, because the planets are close to where the sun will soon rise. If you linger you might gaze at the sun through the telescope and damage your eyesight, said Michelle Nichols, master educator at Chicago's Adler Planetarium.
Ed Krupp, director of Griffith Observatory in Los Angeles, said it will be hard to see the event "with an unaided eye, particularly in an area that is highly urbanized."
The way to find the planets, which will be low on the east-southeast horizon, is to hold your arm straight out, with your hand in a fist and the pinky at the bottom. Halfway up your fist is how high the planets will appear above the horizon, Nichols said.
Jupiter will be white, Mercury pinkish and Mars butterscotch-colored.
"It is a lovely demonstration of the celestial ballet that goes on around us, day after day, year after year, millennium after millennium," Horkheimer said. "When I look at something like this, I realize that all the powers on Earth, all the emperors, all the money, cannot change it one iota."
In ancient times, people thought the close groupings of planets had deep meaning, Krupp said. Now, he said, "it's absolutely something fun to look for."