Venus Blazes In The Pre-Dawn Sky

Look up before dawn this fall and you’ll see a bright object blazing in the eastern sky. Many people mistake it for a plane or even a UFO. But it’s the planet Venus, the brightest object in the sky except for the sun and the moon.

Venus shines so brightly because it’s close to the earth, getting as near as 40 million miles. But it’s also covered by thick clouds that reflect about 2/3 of the sun’s light that falls on it, so it’s like a big round mirror.

Both Venus and Earth are roughly the same size, mass, and composition. For centuries, astronomers thought that because Venus lies just a little closer to the sun, it should exist as a warmer version of Earth, perhaps covered with warm oceans and lush tropical jungles right up to the poles. But it’s not, and one of the great mysteries of planetary science is why Venus turned out to be so hot and nasty, while Earth turned out water-covered, temperate, and teeming with life.

Unlike the Earth, the clouds covering Venus are always there… no sunny days on Venus. And unlike Earth, Venus’ clouds are mostly made of carbon dioxide and sulfuric acid, which keeps most of the sun’s heat trapped in the atmosphere. This “trapping” is called the greenhouse effect, and Venus has the strongest greenhouse effect in the solar system, which is why it’s surface is 460 °C, hot enough to melt lead!

It’s no accident Venus appears at sunrise. Because it lies closer to the sun than us, Venus never lies far from the sun as seen from Earth. Sometimes Venus lies east of the sun and shines in the evening sky, when it’s called the “evening star”. When it lies to the west of the sun, it’s called the “morning star”. In between these appearances for a short period, it lies too close to the sun to be seen. And because it’s closer to the sun, Venus goes through phases, just like the moon. The same is true for Mercury, the closest planet to the sun.

Today and tomorrow are anniversaries of sorts for Venus. Forty years ago, on October 18, 1967 the Soviet probe Venera 4 parachuted into the atmosphere. Before its batteries ran dry, Venera confirmed the surface temperature of Venus was nearly 500 °C. And it was the first to determine the composition of the atmosphere.

Only a day after Venera 4, on October 19, 1967, the American probe Mariner 5 whizzed by just 4,000 km above the cloud tops and measured of the composition, pressure and density of the atmosphere. Despite international tensions at the time, both American and Soviet scientists met to share data and theories on the nature of this strange planet.

When it comes to looking at Venus, remember it’s nearly impossible to see any surface features, even through a powerful telescope. But it’s interesting to see the phases of the Venus. All you need is a small 2 or 3-inch telescope at 80-100x or so. Binoculars aren’t enough. Right now, it’s in a thick crescent phase, like the moon just before first quarter.

But my favorite way to savor this dazzling celestial jewel is just my looking up into the dark blue sky on the edge of daylight and night where, in the words of C. S. Lewis,

“Venus voyages… but my voice falters; rude rime-making wrongs her beauty.”