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"Errors as to the moon and planets are notoriously frequent, Venus and the new moon often being made to rise at sunset." -- STAR NAMES Their Lore and Meaning by Richard Hinckley Allen

Observational Astronomy in Dan Brown's The Da Vinci Code

The pages of the The Da Vinci Code seemed to turn all by themselves, the book was that riveting. I only wished that someone with some knowledge of observational astronomy had proofread chapter 105. In this chapter, night had fallen and a new moon was rising. As the stars were coming out, a point of light brighter than any other was shining in the east -- the planet Venus.

First of all, let's talk about the new Moon. A new Moon happens when the Moon in its eastward orbit around the Earth swings between the Earth and the Sun. Perhaps another term for new Moon could be "dark Moon." The moon, being a sphere, is always half lit and half in darkness. At new Moon, the dark side of the Moon faces Earth while the lit side faces the Sun.

So if the new Moon happens at sunset or nightfall, the new Moon will pretty much set with the Sun. Since the orbiting Moon moves east of the Sun in our sky about 12 degrees per day, you might see the exceedingly thin crescent Moon the day after new Moon. However, conditions would have to be just right, you'd have to be an extraordinarily good observer, and you'd probably need binoculars. The new crescent Moon sets at dusk, not much after sunset.

Even though chapter 105 found "the Scottish countryside spread out before them, suffused in pale moonlight" and the heroine's face "beautiful in the moonlight," this clearly cannot happen at new Moon. You can't even see the new Moon (except its silhouette when the new Moon eclipses the Sun), much less have the light of the new Moon illuminating the landscape.

For the Moon to rise at sunset or early evening, the Moon would have to be full -- or appreciably close to full. Since the Moon is opposite the Sun in our sky when it's full, the full Moon rises about-face of the Sun around sunset. At full Moon, the lit half of the Moon totally faces the Earth.

The Planet Venus

It is true that Venus shines more brilliantly than any other star or planet. It's the the second brightest heavenly body to light up the nighttime -- after the Moon. In fact, eagle-eyed folks can even see Venus at daytime.

But you'll never see Venus in the eastern sky at evening. And you'll never see Venus in the western sky in the wee hours before sunrise. As seen from Earth, Venus is at most a little more than 45 degrees to the east of the Sun at sunset, or a bit more than 45 degrees west of the Sun at sunrise.

The same thing applies to the planet Mercury, except that this planet stays much closer to the Sun. It'll be about 22.5 degrees west of the rising Sun on December 29, and about 18 degrees east of the setting Sun on March 12, 2005. Starting around December 25 and for about three weeks afterwards, look for Venus and Mercury to shine close together in your eastern sky about an hour before sunrise. Binoculars and a clear eastern horizon will definitely be helpful!

Ancient astronomers figured out that Mercury and Venus reside closer to the Sun than Earth does. They came to this conclusion, seeing that these two planets never stand opposite the Sun in our sky and never stay out all night long.

They also knew that the planets Mars, Jupiter and Saturn are farther away from the Sun than Earth is, because at regular intervals these planets are opposite the Sun in the sky. At opposition, a planet shines in the night sky from sunset to sunrise. The ancients, though acute observers of planetary motion, were mistaken in their overall notion that the Sun and planets revolved around the Earth.

That's not to say, however, that all the ancients were mistaken. It's said that the philospher Heraclitus of Pontus (390-310 BC) concluded that Venus and Mercury revolve around the Sun and that the Earth rotates on its axis. Even more amazing -- almost 2,000 years before Copernicus -- the astronomer Aristarchus of Samos (310-230 BC) came up with the idea that all the planets, including Earth, revolve around the Sun. Aristarchus realized that the size of the Sun dwarfs that of the Earth by leaps and bounds, and thought it more likely that the smaller body would revolve around the larger body -- rather than the other way around.

During December 2004 and January 2005, you can see all five visible planets -- Mercury, Venus, Mars, Jupiter and Saturn -- adorning the dawn sky. Click here for a map. For the January 2005 feature, click on the Opposition of Saturn & Other Tidbits.

copyright 2004 by Bruce McClure

Understanding Moon Phases by Deborah Byrd

Moon Phase Calendar

The Dawning of the New Year by Steve Daniels

Previous Features * January 2005 Feature