Three Planets Bunch Up in Twilight

An unusual sight has lined itself up for skywatchers this week. Gaze low toward the west-northwest in the deepening twilight, and three planets will await your view. One is bright; two are much fainter. You can follow them through their celestial gyrations as they shift position day by day, as shown here and below. If you've got binoculars, bring them along — especially if summer haze and humidity are bringing you less than crystal-clear skies.

By far the brightest of the planets is Venus, the "Evening Star." Dimmer Saturn has been closing in on it from the upper left, while Mercury has been closing in on Venus from the lower right. All three planets fit within a circle 5° wide from June 22nd through 29th. They form a remarkably tight bunch on June 25th and 26th, fitting within a 2° circle (about the size of your thumb held at arm's length). This is the best "trio" of planets until at least the year 2030, based on brightness, closeness, and ease of visibility.

After that, Saturn gets lower every day and sinks out of sight, while Venus and Mercury remain closely paired into the first week of July. The crescent Moon will hang with Mercury and Venus on July 8th. Meanwhile, the background stars Pollux and Castor add to the scene, though for these binoculars may be required.

A fourth bright planet is also in evening view, very far off to the upper left of the group of three. This is Jupiter, shining brilliantly high in the southwest (not shown here). Aside from Venus, it's the brightest point of light in the sky — and very easy to spot.

That makes four of the five classical naked-eye planets visible at dusk. The fifth, Mars, is visible before and during dawn, shining orange in the southeastern sky.

All the evening planets appear about the same distance away as you watch them in the deepening dusk, but of course this is an illusion. Mercury is roughly 90 million miles away (its distance changes rapidly); Venus is about 140 million miles away, and Saturn is 930 million miles — about 10 times farther than Mercury. Jupiter is about 500 million miles away.

Such big distances are better expressed by how long it takes light to cross them. Mercury is about 8 light-minutes distant, Venus is about 12 light-minutes away, and Saturn is 85 light-minutes from us. Jupiter is 45 light-minutes distant. By comparison, the stars Pollux and Castor, in the constellation Gemini, are 34 and 52 light-years away, respectively.