Venus-Moon Pairing Tonight: "Special Treat" for Sky-Watchers

Jennifer Vernon
for National Geographic News

Updated March 24, 2004

This evening at twilight, two universal symbols of beauty will shine together in the western sky, creating a stunning sight for North and South Americans.

The planet Venus, the mythological representation of the goddess of love and beauty, will be seen very near the crescent moon, a night object with its own claims to beauty.

"This will be a real head turner," said Alan MacRobert, a senior editor at Sky and Telescope magazine. "You will not have to be some kind of expert astronomer for this. People are going to see this out of their front windshields driving home from work and say, What's that?!"

The pairing of these two bright celestial objects will be plainly visible to the naked eye, MacRobert said, although binoculars could help enhance the experience. "Any old pair of binoculars that you have knocking about the back of a closet some place is a perfectly good astronomical instrument, and you ought to bring it out for this."

"Sister" Planet

Venus is considered to be Earth's "sister" planet because of its relatively similar size. However, with a surface temperature of approximately 700 degrees Celsius (1,300 degrees Fahrenheit) and an atmospheric pressure equivalent to that at an oceanic depth of 2,000 feet (610 meters), Venus is "not nice real estate," MacRobert noted.

Venus, though a planet, is often called the morning star or the evening star. Located second from the sun, Venus is always close to the sun's location in the Earth's sky, MacRobert said, and so is visible only as a very bright spot in the east before sunrise or the west after sunset.

Apparent sky pairings such as the one between Venus and the moon tonight are known in astronomical terms as conjunctions, explained Walter Nissen. Nissen is a career mathematician and a former president of the National Capital Astronomers organization located in Washington, D.C.

Conjunctions occur only because the planets in this solar system (with the exception of Pluto) and Earth's moon lie within the same plane, Nissen said. These objects share the same plane because they all formed from the same thin disc of dust that orbited the sun at the time the solar system developed.

Venus itself goes through five apparitions, or phases of visibility, over an approximate eight-year time span, Nissen said. Currently, Venus is going through a highly visible phase and will be at its greatest brilliancy on May 1.

A unique conjunction between Venus and the sun will occur on June 8 of this year. Known as the transit of Venus, this event involves the apparent passage of Venus in front of the sun. This event, which last occurred in 1882, can be witnessed only with the use of special protective filters, Nissen cautioned.

Visual Illusion

Although Venus's title as morning and evening star is a misnomer, it is easy to understand why early astronomers thought this bright, constant light to be one. A rough guide for determining the difference between a star and a planet is whether the point appears to flicker. The reason for this visual illusion, Nissen explained, is that the amount of light reflected from a planet that reaches an observer's eye without disruption is greater than that of a star, which is much farther away and so appears to flicker.

Venus is not the only planet that will conjoin with the moon in March, Nissen said. For observers in northern latitudes, Mercury will be near the moon very low in the west around March 21 and 22. The moon and a very faint Mars will pair on March 25 followed by a pairing of the moon with Saturn on March 28. This last conjunction will be very difficult to see by sunset, Nissen noted.

Dark Sky Is a Privilege

Tonight's conjunction of Venus and the moon is a special visual treat, said Nissen, given that objects in the night sky normally are obscured by competing light sources on the Earth's surface. "Unfortunately, a dark sky is a privilege that very few so-called civilized people are able to experience anymore," Nissen commented.

While ancient civilizations may have used these celestial meetings to determine portents and omens, modern-day astronomers have no such illusions.

"We know now that they're not gods," said MacRobert, a physics major and 21-year veteran at Sky and Telescope. "They're not looking down on us dispensing good luck and bad luck … We've sent probes up to Mars. They have not landed on the hairy chest of a god; they've landed on a ball of rock."

Yet it can be hard to look at the night sky without a sense of wonder. "I don't think there's a human alive that … [is] not fascinated by it," remarked Nissen, who co-founded the SeeSat-L e-mail list for satellite observers. "We live under it … yet many people just ignore it. They never take anything from the sky."

For those people, Nissen has some words of advice: "Take a couple hours … off from your normal life and take a chaise lounge and some appropriate beverages and just watch the moon. It's an incredibly, strikingly beautiful thing, and there's no walking away from that."

MacRobert agrees. "Things like this [conjunction], that get people to look up, take us out of our tiny little lives on this tiny little world … and make us realize that we have a place in a much larger universe, a much larger scheme of things. And that is important to stop and think about from time to time."

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