Amateur astronomers wanted for planet hunt

The project seeks to obtain information about extrasolar planets that "transit" or pass in front of their parent stars.

May 1st, 2003

Astronomy has come a long way since the days of Gallileo and Newton. Most professional astronomers would say that it's no longer possible for the "gentleman astronomer" to make a significant contribution to the field. Or is it? Two professional astronomers have come up with a way for enthusiastic amateurs to become involved in serious work as part of a team researching extrasolar planets (those planets that are outside our solar system). About 100 extrasolar planets have been discovered in recent years.

The two researchers are Tim Castellano, an astronomer from NASA Ames Research Center (Mountain View, CA), and Greg Laughlin, an assistant professor of astronomy at the University of California, Santa Cruz, and their project is called Transit Search (more details at The project seeks to obtain information about extrasolar planets that "transit" or pass in front of their parent stars. Such information can indicate the size of a planet, reveal its atmospheric composition, and possibly confirm the presence of rings or orbiting moons.

The amateur astronomers will need equipment that is readily available commercially—a telescope whose primary mirror is around 8 to 10 in., software that can control the telescope's built-in tracking system, a CCD (charge-coupled device) imager that attaches to the back of the telescope, and a laptop computer with data-analysis software that can readily be found on the Internet. The whole setup should cost less than $5000, the two research astronomers suggest. Indeed, many amateur observers already possess such equipment.

The technique used by the amateur observers is called differential photometry. This technique allows the astronomer to measure the ratio of the brightness of a target star and one or more comparison stars. With CCDs, which allow the simultaneous imaging of many stars, differential photometry is relatively easy. Single-channel photometers are also used for differential photometry, but because the telescope must be repositioned from star to star to make one measurement, brightness corrections may be necessary.

The first amateur to observe a transiting planet was a Finnish astronomer, Arto Oksanen, who charted the passage of a planet across the star known to astronomers as HD 209458 using off-the-shelf equipment. That star is 47 parsecs (153 light-years) away from Earth in the constellation Pegasus. Amateur astronomy is very popular in Finland where the skies are often clearer than in other industrialized countries.

Castellano and Laughlin are searching for similarly enthusiastic amateur observers who have the necessary equipment and are prepared to spend many nights on the lookout for the rare occurrences of a planetary transit. Amateurs have the time to spend on the planet hunt and, what's more, they do so for free. To aid the amateurs, Castellano and Laughlin have posted a list of stars and their potential transit dates and times on the Transit Search web site.

Any transiting planets discovered by the amateur network will be confirmed by professional observers in the Lick Observatory Planet Search Program, and any publication of those discoveries will credit the participating members of the detection network as the discoverers. But discovering transiting planets is not an easy task. "The signature of a planetary transit is very subtle, so multiple simultaneous observations will provide a vitally needed redundancy," says Laughlin. Observers may take several months to get the technique correct, notes the researcher.

In assisting with this research, amateur astronomers will be keeping a grand tradition alive.

In 1781, William Herschel found Uranus using an amateur telescope he built at his home. Herschel later became the British Royal Astronomer. American Clyde Tombaugh found Pluto in 1930 when he was only 23 and he later became a professional astronomer at New Mexico State University. You, too, could join the ranks of the planet hunters.

Jeffrey Bairstow
Online Editor

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