Step outside as evening twilight fades, and from now through the middle of August you'll find three planets shining low in the west - one much brighter than the other two. All you'll need is a clear sky and an open westward view about an hour after sunset.

"Venus will leap out at you," says Alan MacRobert, a senior editor of Sky and Telescope magazine. "Saturn and Mars are fainter, so you may need to wait for the sky to darken a bit more before they glimmer into view."

Venus is the famed "Evening Star," the brightest celestial object in Earth's sky after the Sun and Moon.

Saturn and Mars are only about 1 percent as bright. They form a more-or-less horizontal line above Venus, as wide as three or four fingers held together at arm's length. Saturn and Mars will spend the week sliding to the right with respect to Venus, creating a planetary triangle that changes shape from day to day.

Although the three planets look close together, they're not. Venus is currently 6 light-minutes (73 million miles) from us, Mars is 17 light-minutes (190 million miles) distant, and Saturn is far in the background 85 light-minutes (950 million miles) away.

Three reasons combine to make Venus shine so much brighter than the others. It's the closest to us, it's the closest to the Sun so it's illuminated more intensely, and it's covered with brilliantly reflective white clouds.

As for Mars and Saturn? They look similar in brightness for reasons that cancel out. Saturn is 35 times larger than Mars, but it's much farther both from us and from the Sun.

The crescent Moon joins the twilight planet scene on Thursday, August 12th (when it's below Venus) and Friday the 13th (when it's left of Venus).

"Don't miss this chance to do some easy astronomy from your backyard, balcony, or rooftop," says Sky and Telescope editor in chief Robert Naeye. "It's a big universe, and planets await!"

For more skywatching information and astronomy news, visit SkyandTelescope.com or pick up Sky and Telescope, the essential magazine of astronomy since 1941.