SkyCaramba weekly astronomy blog for the week ending November 19, 2011
Venus is becoming visible again in our evening skies. Those in the southern hemisphere have the best view right now. Viewers in the north will have to wait a few weeks for the view to improve. But you may find it close to the horizon just above the trees.
Venus is closer to the sun than Earth. That’s one reason it’s such a hot world. Temperatures there reach 860 degrees Farenheit (460 Celcius). Another reason is the carbon dioxide atmosphere. The gas, now considered a greenhouse gas contributing to warming temperatures on Earth, is abundant in Venus’s atmosphere.
The heat and the atmosphere made of stuff humans exhale are enough to make Venus unwelcoming. The sulfuric acid clouds add to it. Those clouds ate away at several spacecraft before scientists understood why the probes didn’t last long.
The sulfuric acid clouds are also why Venus shines so brightly in the sky. They reflect most of the sunlight that reaches them. We can’t see Venus’s surface through them. But the surface has been mapped by orbiters hitting the planet with radar beams.
Even though you may have heard that planets don’t twinkle, bright objects low on the horizon often do. And Venus sometimes resembles sparklers kids play with on some holidays, including Independence Day in the United States. It’s occasionally mistaken for a flare lit by lost hikers in distant mountains. And a few police departments have received calls about an unidentified flying object that turned to be Venus.
Because Venus is closer to the sun than Earth, it never reaches the opposite side of the sky as the sun. In other words, it never reaches opposition. Instead it gets as far away from the sun as it can in the sky. At that time it’s said to be at greatest elongation. For Venus, that’s about 46 degrees either in the morning sky (western elongation because it’s west of the sun) or in the evening sky (eastern elongation because it’s east of the sun). Venus will be in our evening sky for a few months before it’s at greatest elongation. Keep watching and see how high the planet gets in late March.
Being closer to the sun than Earth causes Venus to have its dark side pointed toward us much of the time. Just like the moon, the planet may look like a thin crescent, a semi-circle, a gibbous circle, or a nearly full circle. You have to look at it in a telescope to see that. It’s tempting to describe a “first quarter Venus” but astronomers don’t do that. Take a look though and sometime you may be surprised at how thin the crescent is, yet the planet shines so bright!
And there’s one more thing about being closer to the sun that makes Venus an awesome planet to have in our solar system. Just like the moon occasionally passes between the earth and sun, so does Venus. That’s called a transit of Venus and the next one happens in June 2012. People who take special care to view the sun without harming their eyes will see the big circle of the solar disk with a dot crossing it. Most of the best viewing area for the 2012 transit will be from the Pacific Ocean. Unfortunately, most people won’t be on ships or visiting the islands there to get those good views.
There’s some suspense for you as you watch Venus over the next few months knowing what’s in store for it in the summer.