On May 26, when the grouping is tightest, you can almost cover the triangle of planets with your thumb at arm’s length. (Stellarium.org)

A slow-motion planetary pile-up begins in the sky this week. From May 24 to 29, 2013, Mercury, Venus, and Jupiter appear within 5 degrees of one another (half the width of your fist held at arm’s length), low at dusk in the west-northwest.

Why go out to look for these planets?

1) You won’t get another sight quite like this for 13 more years. This is the tightest grouping of three planets visible without binoculars until 2026, according to Sky & Telescope.

2) This is an excellent opportunity to spot the most elusive of the naked-eye planets, Mercury. Perhaps you are like my skeptical officemate and have become convinced that Mercury does not actually exist because you’ve never seen it. This is your chance to have two other planets—bright ones—to help point the way.

3) You’ll get the sense that planets really do move. Watch each night and witness the ever-changing configurations of Mercury, Venus, and Jupiter.

Tips for seeing this planetary grouping:

  • When: Any clear evening between May 24 and 29, from about 30 to 45 minutes after sunset. Choosing that time balances two considerations: a) the sooner it is after sunset, the brighter the sky will be, making it more difficult to pick out the planets, and b) the longer it is after sunset, the lower the planets will be in the sky, which can also make them difficult to see; if you really wait too long, these planets will disappear below the horizon.

Arrgh, a tree is in the way! To see the planet trio, be sure to find an unobstructed view to the west-northwest. (Stellarium.org)

  • What direction: Over the spot where the Sun set (west-northwest)
  • Where to go: Somewhere with an unobstructed view in the direction the Sun went down
  • What to bring: Just your eyes are needed. But if you have binoculars, you will probably be able to fit all three planets in the field of view. If you can hold the binoculars steady (or use a tripod), you may also glimpse some of Jupiter’s moons.

Of course, the planets aren’t really piling up on top of one another. Even when planets lie in roughly the same line of sight from our perspective on Earth, they are still many millions of miles apart.