Bob Doyle

Bob Doyle

Late this fall, the brilliant planet Venus will appear low in the western dusk, then climb higher during the winter.

Here are some basic facts about Venus: It has an orbit about 0.7 as large as our orbit around the sun, so it receives about twice as much sunlight as Earth per square foot. Venus takes 225 Earth days to orbit the sun.

Venus is about 95% as large as the Earth with about 82% as much mass. The surface gravity on Venus is 91% that of Earth’s. Then the similar quantities end. The atmosphere of Venus consists mostly of carbon dioxide; at Venus’ surface, the air pressure is over 90 times the air pressure at the Earth’s surface.

The average surface temperature of Venus is 870 degrees!, hot enough to melt some metals. Venus’ clouds extend to a height of 43 miles above its surface. Our highest clouds (top of thunderstorm clouds) go as high as 12 miles. The clouds of Venus seem to consist mostly of droplets of sulfuric acids (compared to the water droplets and ice crystals of our clouds).

Venus rotates very slowly, taking 243 Earth days to spin around backwards. Radar mapping (which can penetrate Venus’ clouds) reveal a volcanic surface with two huge plateaus, big volcanic mountains and many lava flows.

Venus, unlike the Earth, doesn’t have crustal plates or plate motion (which cause our earthquakes and volcanoes). Needless to say, Venus has no oceans, its water having long ago escaped into space.

Aside from the above facts, orbiting space probes (European Space Agency’s Venus Express and Japan’s Akatsuki) have studied Venus’ atmosphere using infrared and ultraviolet cameras. Through optical (light collecting) telescopes, Venus shows a nearly featureless disk, except for its phases (like our moon).

The Venus Express probe went into a polar orbit while Akatsuki is in an equatorial orbit. The winds in Venus’ upper cloud layers rotate around Venus at a speed of 200 miles an hour, 60 times as fast as Venus’ surface rotation rate and circling the planet every four Earth days.

At Venus’ surface, the winds are very slow, a few miles an hour (as measured by Russia’s Venera probes which landed on Venus’ surface). There are three layers of Venus’ clouds — lower clouds at 30 miles height, middle clouds at 33 miles height and upper clouds up to 43 miles high.

It is at the top of the upper clouds where the rotation is the fastest. (Speeds of these winds is through the Doppler effect, the stretching/compression of heat or ultraviolet rays by motion. Police use this effect to determine car speed.)

The clouds are critical because most of Venus’ sunlight is absorbed by these clouds. There is an unknown molecule within the upper clouds that is absorbing about half of Venus’ solar energy. The reflection of sunlight seems to vary with time, possibly because this unknown absorber may vary in concentration.

The Venus Express found a whirling vortex in the clouds at Venus’ south pole that can be 20 miles deep , similar to the pattern of water going down a drain. Reference: The Planetary Report, September 2019 issue.

SKY CONDITIONS IN THE WEEK AHEAD: Dawn begins at 6:20 a.m., sunrise at about 7:18 a.m., midday at 1:03 p.m. Sunset at about 6:47 p.m. and dusk ends at 7:45 p.m. Daily sunlight lasts 11 hours and 27 minutes. Each day, there is about two minutes less sunlight than the previous day.

Jupiter and Saturn can be seen in the southwest at dusk with Jupiter being much brighter than Saturn. Both planets shine more steadily than the night stars.

Bob Doyle, professor emeritus at Frostburg State University, invites any readers comments and questions. E-mail him at He is available as a speaker on his column topics.

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