Professors at Iowa State are part of a unique international astronomy effort.

Steve Kawaler, professor of physics and astronomy, and Reed Riddle, assistant scientist in physics and astronomy, head a team known as the Whole Earth Telescope, which consists of more than 60 international astronomers located in 16 countries around the world.

The rotating motion of the Earth prevents a single telescope in one geographical location from observing a star all the time. Therefore, the strategy is to use several observatories around the world to observe the star and gather data collectively, sending it to the headquarters in Physics Hall.

“Most collaborations in astronomy are relatively small, involving five to six people at most,” Kawaler said. “But WET is large because we have to cover the globe.”

Kawaler said location is an important consideration when deciding who may join the project.

“The No. 1 criteria to join the collaboration is eagerness to be involved in the science, closely followed in by number two, being in an interesting longitude,” Kawaler said. “The goal is 24-hours-a-day coverage of stars, and you can’t do that from a single point on earth, except for the poles.”

The Whole Earth Telescope organizes observing campaigns twice a year. The astronomers observe and analyze a type of star known as a pulsating variable star.

Kawaler described these as “stars that change their brightness periodically.” More specifically, the group is interested in white dwarf stars, which is what the sun will become in a few billion years.

Astronomers capture the rapid pulsations, which human eyes and photographic plates cannot detect, by using photoelectric and Charge-Coupled Device (CCD) photometers.

“The basic WET photometer is a three-channel photomultiplier tube (PMT),” said Riddle, associate director of operations for WET.

“Each PMT converts the light that hits it into an electronic signal. This signal is then sent to a computer for collection,” he said. “We use three channels: one for the target, one for the background sky and one for a comparison star.”

Riddle said the two extra channels allow for the removal of variations, such as moonlight and clouds, from the target’s light curve. Some sites are already equipped with the more expensive CCD photometers, while Riddle said others would convert from PMT to CCD photometers in the future.

“The telescopes themselves range from a 24-inch telescope on Mauna Kea to an almost three-meter telescope in the Canary Islands,” Riddle said.

“The science we get out of that is terrific. We are able to probe the inside of a star, because what we are seeing are basically star quakes,” said Kawaler, referring to a phenomenon known as stellar seismology.

Managing an organization the size of the WET presents several challenges.

“The hard part is before the run, selecting a target to look at, agreeing among 50 people that this is the target we are going to look at,” Kawaler said.

“Then applying for telescope times at different places, making sure the applications are all for the same period of time, coordinating with any other facilities, like the Hubble Space Telescope.”

One student said the Whole Earth Telescope drew his interest from across the globe.

“The reason I came to study here at ISU is because of WET,” said Maja Vuckovic, graduate student in physics and astronomy from Yugoslavia.

The next campaign will be in early May, when scientists will be observing two different stars: a white dwarf, also known as a hydrogen-deficient star, and PG1159-035, which Kawaler said is one of the older favorite targets for the team of astronomers.