"Its day is longer than its year"

NASA's Pioneer Venus probe captured this image of Venus' perpetual cloud layer in 1979.

Last Friday around sunset I joined the regular Central Park stargazers at the northeast corner of the Great Lawn to look at the approaching conjunction of Venus and Mercury, and to see those two planets and Saturn in a single binocular field of vision [that is, to see the three very close to each other].

While there I got into a conversation with Tom Clabough, one of the astronomy Regulars, and asked a question about the atmosphere of Venus. He told me lots of interesting stuff and then a few days later sent me an e-mail generously clarifying what he had said. You may enjoy reading it as much as I did:

Recall Friday evening we discussed the atmosphere and clouds of Venus and I believe I said (correctly) that nearly all of its atmosphere is carbon dioxide(96-98%). However, I think I also said that the clouds consisted mostly of carbon Monoxide. This is not correct. Although there is some CO in the Venus atmosphere the clouds are mainly made up of tiny droplets of sulfuric acid (ie, battery acid!) which rains down onto the hot (875 deg) surface.

The planet spins "backwards" and its day(246 earth days long) is longer than its year(225 earth days long). Mysteriously, its atmosphere whips around the planet in just 6 earth days, much faster than its 246 earth day long rotational period. The nearest the planet gets to earth is about 23 million miles, and it is the high clouds that reflect nearly all of the sunlight which strikes the planet and which makes it appear so bright in our sky.