Finding faraway planets hard, but Venus sight to see

Greetings stargazers. Last month I talked briefly about the astronomer Johannes Kepler, and his contributions to astronomy by describing the motions of the planets. This month I will talk about a current science mission named after him.

One of the most exciting space probes flying today is the unmanned Kepler mission to search for planets around other stars. One important method used is actually quite simple. A very sensitive camera watches a select group of stars to see if any get dimmer when a planet crosses in front of them. Although the chance for an earthlike planet to cross in front of one of the stars is less than one-half of 1 percent, it is quite a large set of stars that is being monitored – more than 145,000 “middle aged” stars.

As of December 2011, the total number of candidate planets was 2,326. Many of these planets are large, Jupiter-like planets that are close to their parent star, but some fall into the Earth-like category. Like the sun, most stars have more than one planet. There is an excellent Wikipedia article if you want to know more about this mission.

It is remarkable that cameras can detect such a small variation in brightness. Your eye can detect the brightness of things over a wide range, but it can tell the relative difference between two objects of similar brightness to only a few percent. (Or about one-fourth of an f-stop for you photographers.) The camera on the Kepler spacecraft has a sensitivity measured in parts per million. However, even with this, it is a challenge to identify some planet transits, because most stars, including the sun, vary in brightness by a few parts per million. An Earth-like planet transiting a relatively small star like the sun would reduce the light detected by about 100 parts per million.

This month

If you enjoyed the recent eclipse, then you should be ready for an even more unusual event. On June 5, Venus will cross in front of the sun. This last happened in 2004, but won’t happen again until 2117, so this will be the last time to see it for most of us.

Watch the sun safely. Many used a pinhole to view the eclipse. This might work for the transit, but because the diameter of Venus is only about 1 percent of the diameter of the sun, you likely would need a smaller pinhole and greater distance to your image. The Durango Discovery Museum should have telescopes set up for the transit.

If you have nonmagnifying solar-viewing glasses, I am not sure if the transit will be visible because of the small size of Venus. This might be a good test of your visual acuity.

Even though daytime astronomical events are fun, don’t forget to go outside after dark for some stargazing. The summer Milky Way now is rising and makes a great target for a pair of binoculars. Scores of star clusters and a few bright nebulae should be visible.

hakes_c@fortlewis.edu Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.

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