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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