Venus, Mars and Jupiter Line Up for a Rare Show : Astronomy: The planets will be in a tight formation for the next few nights. They will be joined Saturday by a crescent moon in the western sky.

For those who prefer their scenic wonders to be of the more subtle variety, the heavens will put on a rare show in the next few nights when three planets form a tight formation as they drift across the western sky.

Venus, Mars and Jupiter will fit within a circle of the sky measuring only two degrees--less than four times the diameter of the moon--a configuration that occurs on average only about once a century. The “massing of the planets,” as it is called, will be visible in the western sky in the first few hours of darkness, weather permitting.

The view Saturday could be especially enchanting because the planets will be accompanied by a crescent moon. The planets will be closest together on Monday evening when they will form a circle only 1.8 degrees wide.

The planets will actually be very far apart, but they will appear to be close together because they will fall on the same line of sight when viewed from the Earth. Venus will be about six light-minutes away, meaning it will take light, traveling at 186,000 miles per second, six minutes to travel from Venus to Earth. Mars will be about 18 light-minutes away, and Jupiter, the largest planet in the solar system, will be about 50 light-minutes away.

The planets form this alignment only rarely, and at very irregular intervals. Not once during the entire 19th Century, for example, did the three planets appear to be this close together.

Oddly enough, the planets will be nearly this close again in 4 1/2 years, according to Griffith Observatory. But they will not be closer together until March 7, 2152, and they will be too close to the sun to be seen.

So the next opportunity to actually see the planets this close together will not come until Aug. 1, 2277.

Planets are especially attractive to many stargazers because even a small telescope will sometimes reveal startling results. Because of the tight grouping, observers who might have trouble finding Jupiter in the night sky should be able to locate it easily during this period.

And even a small telescope will reveal the astonishing role that Jupiter played in the development of human perception of the universe. Four centuries ago, using a spyglass to study the heavens, the Italian mathematician Galileo Galilei saw the four moons around Jupiter for the first time.

The discovery was one of the bits of evidence that convinced Galileo that the universe does not revolve around the Earth. In observing Jupiter, he could see other bodies revolving around a planet, and that helped convince him that the planets, including the Earth, revolve around another body--the sun.

A CLUSTER OF PLANETS

The heavens will put on a rare show the next few nights when three planets--Venus, Mars and Jupiter--cluster together in the western sky. That tight “massing of the planets” only happens about once each century. Saturday, the planets will be accompanied by a crescent moon, and they will be closer together on Monday than they will be until the year 2152. Venus will be the brightest of the three, but Jupiter should also be bright. Mars will be faint.

Source: Sky & Telescope Magazine