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March 2004 Feature: Mercury Joins Springtime Planetary Festival


At the beginning of March, four planets -- Venus, Mars, Saturn and Jupiter -- light up the starry sky at nightfall. Make friends with them now and they'll introduce you to reclusive Mercury at this year's springtime planetary festival.

First of all, look for Venus at early evening. It's the overwhelmingly brillant "evening star" lording over the western sky. In fact, sharp-eyed people can see Venus even before sunset.

Then turn about-face from Venus to see Jupiter in the east, rather close to the horizon. If your view eastward is obstructed, no need to worry. The sky's second brightest planet rises upward throughout the night whereas Venus descends for the western horizon. Venus sets some four hours after sunset, at which time Jupiter reigns supreme for the night.

Just like that, you have two planets under your belt. And "belt" is the key word right now, because these planets always travel upon a belt of stars known as the zodiac. This belt is easy to envision with the mind's eye with the location of just one more planet.

At nightfall in early March, the constellation Orion, the hunter, stands tall in your southern sky. Often distinguished by its belt of three stars, Orion sports a bright blue-white star to the lower right of the belt named Rigel, and a bright ruddy star to the upper left of the belt called Betelgeuse (often pronouced "beetle juice"). Drawing a line from Rigel through Betelgeuse shows you a third planet -- bright golden Saturn, which stands out at twice the distance of Betelgeuse. See star chart.

Once you find Saturn, draw an arc from Jupiter through Saturn and down to Venus, and presto, you've drawn the path of the planets through the zodiac. Oftentimes, this road is called the ecliptic. The planets are found on or near this roadway that passes dead center through the zodiac's band of stars. The ecliptic at early evening spans the sky from east to west, arching high over the constellation Orion.

In early March, you'll see Mars on this arc roughly three-fourths the distance from Saturn to Venus. But since Venus travels more rapidly in its orbit than does Mars, Venus gains on Mars all through the month. In late April, as a matter of fact, Venus and Mars meet up and shine together in the evening sky.

Enter Mercury onto the Evening Stage

On March 20, when the spring equinox takes place, Mercury joins the planetary parade. Mercury, the innermost planet of the solar system, stays closely tethered to the Sun -- much of the time lost in the Sun's glare. It's only when Mercury swings to the outer edge of its orbit as seen from Earth that the planet sneaks on stage -- either shortly before sunrise or after sunset. Mercury's best evening appearance of the year comes in late March and early April.

You need an unobstructed view to the west to see Mercury -- even then. Around the equinox, Mercury sets about one hour and fifteen minutes after the Sun. The shy planet comes out of hiding about thirty to forty-five minutes after sundown. To locate it, draw a line from Saturn through Mars and just left of Venus and down to the horizon. Expect to find Mercury not much above the horizon -- and almost due west, about where the Sun sets at this time of year. On March 21, Mercury resides to the upper right of the exceedingly thin crescent Moon. On the day following -- March 22 -- the planet resides to the crescent Moon's lower right.

Fortunately, Mercury sets later day by day. A week after the equinox, Mercury stays out for a maximum of about an hour and forty minutes after sunset. After that, Mercury should offer decent viewing till the end of the first week of April.

copyright 2004 by Bruce McClure

All Five Planets Chart, courtesy of Earth and Sky