All five planets that can be visible to the naked eye will appear together in the evening sky later this month in a viewing opportunity that won't be matched for 32 years.
Going in order from West to East, the cast of planetary characters will be Mercury, Venus, Mars, Saturn and Jupiter. All but Mercury are already visible. The winged messenger is the most elusive of the five, being so close to the Sun that it never gets very far above the horizon, and always only near dawn or dusk.
By late March, Mercury will be about as high as possible at dusk for viewers at mid-northern latitudes, setting the stage for a memorable few weeks of easy-to-do backyard skywatching.
Where to look
Mercury will hover above the setting Sun in the West. Higher up, brilliant Venus already dominates the stage, outshining all stars and planets. Mars, much dimmer than it was last summer, is high in the southwestern sky. Saturn is nearly overhead now at dusk and to the south. Jupiter, now stunningly bright, is king of the eastern evening sky, rising just as the Sun goes down.
Robert C. Victor, a long-time astronomer at the Abrams Planetarium at Michigan State University, now retired, has for some four decades specialized in predicting and observing unusual configurations of the planets. Victor said there won't be a more easily observed display of all five naked-eye planets at dusk until April 2036.
"I would like to encourage astronomy clubs and planetariums to schedule twilight public viewing sessions during March 22-31, including the final weekend, March 26-28, for this wonderful occasion," Victor said. "Sessions should begin by about 45 minutes after sunset, to insure catching Mercury before it sinks too low."
Armed with a simple sky map, people can find the planets on their own from any backyard. Each of the planets will be bright enough to be seen under most urban lighting conditions, too.
The setup is possible this month because all of the planets are on the same side of the Sun, as envisioned from above the solar system. The planets create no light of their own, of course, but shine by reflecting sunlight.
A wide variety of different configurations involving the planets typically occur during the course of any given year. It is quite unusual, however, to spot the five brightest planets in the sky at the same time.
According to Jean Meeus of Belgium, a specialist in spherical and mathematical astronomy, there are 12 similar cases between the years 1980 and 2020. But, he also points out that some of these (such as in August 2016 and July 2020) will be difficult to enjoy because some of the planets will be very low in the sky.
Victor notes that there will be another fine chance to view all five planets -- in the morning sky -- during late December 2004 through early January 2005.
From our earthly vantagepoint, we can readily observe Mercury, Venus, Mars, Jupiter and Saturn with our unaided eyes when they are favorably positioned in their orbits around the Sun. Each of these planets appears to move against the starry background at their own speeds and along their own tracks. Since they are constantly moving at different speeds in relation to other objects, the positions of all five planets at any particular time is unique to that moment.
The ecliptic and the zodiac
All of these naked-eye planets – and the Moon as well – closely follow an imaginary line in the sky called the ecliptic. The ecliptic is also the apparent path that the Sun appears to take through the sky as a result of the Earth’s revolution around it.
Technically, the ecliptic represents the extension or projection of the plane of the Earth’s orbit out towards the sky. But since the Moon and planets move in orbits whose planes do not differ greatly from that of the Earth’s orbit, these bodies, when visible in our sky, always stay relatively close to the ecliptic line.
Twelve of the constellations through which the ecliptic passes form the Zodiac; their names can be readily identified on standard star charts, and they are also familiar, at least in name, to millions of horoscope users.
Ancient man probably took note of the fact that the planets – themselves resembling bright stars – had the freedom to wander in the heavens, while the other "fixed" stars remained more rooted in their positions. This ability to move seemed to have an almost magical, god-like quality. And evidence that the planets came to be associated with the gods lies in their very names, which represent ancient deities.
As a bonus to the planet panorama, the Moon will wander within the span of the five worlds during the interval from March 22 through April 1. Some highlights, according to Victor:
- Monday, March 22: At dusk a thin crescent Moon will appear low in the West, not far to Mercury’s upper left," Victor said.
- Wednesday, March 24: The waxing crescent Moon will appear close to brilliant Venus.
- Thursday, March 25: The Moon will be close to Mars, making the red planet, now rather dim, easier to locate.
- Saturday, March 27: The array of five visible planets will span 135 degrees across the sky. Astronomers divide the sky into degrees as seen from Earth's surface. The Moon is one-half degree in width. Your fist held at arm's length covers about 10 degrees of sky.
- Sunday, March 28: The First Quarter Moon will appear above Saturn.
- Friday, April 2: The waxing gibbous Moon will appear not far to the lower left of Jupiter.
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