Venus Gets A Visit From The Moon

Venus and the fingernail moon team up in the western sky tonight and tomorrow night. Stellarium

Look west tonight and you’ll see Venus has company. A thin, 2-day-old crescent will dangle below the brilliant planet at dusk. The sight will be a beautiful one and worth catching while you’re out and about. If clouds interfere, a slightly thicker, brighter moon will appear to the left of Venus on Saturday evening.

Venus is all deception. Bright and shiny, you’d think it was all heavenly light, but beneath the clouds is a hot, barren and desolate landscape. With an average planet-wide temperature of about 880°, it’s almost twice as hot as your oven. And the atmospheric pressure is 92 times that of Earth, enough to crush a submarine. The tremendous heat and pressure turns the planet’s crust into something like Play-Doh, very different from Earth’s more brittle crust.

This 4,800-foot-high volcano on Venus, called Sapas Mons, is about 250 miles (400 km) across. Large lava flows are seen in the foreground. The image was made by NASA’s Magellan spacecraft that uses radar to penetrate the planet’s clouds. This 10 times vertically exaggerated view was produced from Magellan radar data. NASA / JPL-Caltech

Venus has more than 1,600 large volcanoes and thousands of little ones. Most of the Venusian variety grew over “hot spots” in the planet’s crust where magma rose to the surface in pulses to build towering volcanic peaks. Most of Earth’s volcanoes in contrast form along plate boundaries, where great rafts of crust dive back into the mantle to be remelted and recycled. Venus doesn’t appear to have plate tectonics like Earth probably because it lost its surface water long ago. More about that in a second. Today, nearly all of Venusian are inactive though there’s evidence of at least one geologically recent eruption.

What most overwhelms the senses is the sheer, baking heat under its oppressive atmosphere. Venus is closer to the sun than the Earth and receives more heat. This caused its early water sources, likely an ocean, to evaporate at a higher rate. Water is a greenhouse gas. It acts as an insulating blanket, trapping heat rising from the sun-warmed planet. With more of it in the atmosphere, Venus grew even warmer, which caused even more water to evaporate in a runaway greenhouse effect that ultimately left the planet’s surface bone dry.

The Sun’s rays pierce through the cloudy Venusian atmosphere and warm the planet’s surface. As the heat rises from the surface it becomes trapped below the cloud layer by carbon dioxide, which comprises 97% of Venus’ atmosphere, creating a powerful greenhouse effect. ESA

Meanwhile, ultraviolet rays from the sun broke apart the water vapor into hydrogen, which being light, escaped into space, and oxygen. The oxygen reacted with the surface minerals. While this was happening, volcanoes were pumping carbon dioxide into the atmosphere. On Earth, the oceans absorb a lot of CO2, removing it from the atmosphere. Plants also use carbon dioxide to make food. Without oceans and life to stow away excess CO2 the gas steadily accumulated in Venus’ atmosphere. Since it’s also a potent greenhouse gas, carbon dioxide helped make the planet even hotter, leading to the hellish conditions we know Venus for today.

Like Dr. Jekyll and Mr. Hyde, Venus keeps its secrets well-hidden beneath a perpetual layer of serenely white clouds. On the good Earth, summer nights can be hot and sweaty, but they’re nothing compared to 10 seconds on Venus.

6 Responses

  1. I just saw Venus to the upper right of the moon. I needed to block out the sun to find the moon up and to well to the left of the sun. Then I needed binoculars to see Venus. That was 4pm EDT near NYC. Maybe you’ll have the same view at 4pm CDT !

    1. astrobob


      It’s quite a kick to see Venus in daylight. Wish I could see it here — we’re cloudy 🙁

          1. caralex

            It won’t set after midnight here during this apparition, but in 2015, in late May, it was setting half an hour after midnight!

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