Picturing the Sun
Sun's Energy Focus of New Airborne Telescope

You don’t have to be a scientist to know the sun has an energetic flair for the dramatic – look no further than last year’s news reports of solar disturbances hurling radiation at satellites and sparking Northern Light displays as far south as Florida and Texas.

But APL researchers have started looking into a lesser known and longer-term aspect of the relationship between the sun and Earth. Using a new airborne telescope that can actually “see” the energy coming from separate features on the sun’s surface, they’ve gathered new information that could one day help scientists forecast changes in solar irradiance – the energy from the sun absorbed in Earth’s atmosphere – that might affect our global climate.

Dave Rust, Pietro Bernasconi and Harry Eaton are part of an APL team working on the Solar Bolometric Imager project, a sensitive telescope-camera package designed to record the full range of irradiance sources on the sun. Coming off a short but successful balloon-flight test in September 2003 – which proved that a telescope could precisely chart hot and cold patches on the sun – the team is now sifting through and calibrating SBI images.

“Much of this goes into the big problem of trying to figure out climate change, and sorting out the relative effects of human activity and the effects of the sun,” says Bernasconi, SBI project scientist. “Eventually, this will help create better models for those trying to figure out what’s happening to Earth’s atmosphere over long time intervals.”

TEST FLIGHT
The SBI was developed by Peter Foukal of Heliophysics, Inc., of Nahant, Mass. In addition to refining the telescope’s electronic systems, APL provided the stabilized gondola and computer systems and operated the device during the Sept. 2003 flight test at Fort Sumner, N.M. The retrofitted gondola was the same that completed two successful flights of the Flare Genesis telescope, which gathered critical data on sunspots and magnetically active regions on the sun’s surface in 1996 and 2000.

A 300-foot-wide balloon carried SBI some 20 miles above the ground, where for seven hours, free of the atmospheric absorption that hinders such imaging from the ground, it snapped more than a half-million images. The instrument’s broad spectral capabilities allow it to measure light from the ultraviolet through the infrared with the same sensitivity, making it the first telescope that can so precisely compare the energy coming from dark sunspots, the bright, torch-like features on the sun’s limb called faculae, and the “quiet” areas between them.

Rust, the project’s principal investigator, says one of the first questions the data might be able to answer is whether the sun undergoes subtle variations in brightness besides the well-known changes during solar maximum – the busiest period during the 11-year cycle of solar activity. The data can also serve as a solar time capsule, allowing researchers to finally correlate recurring features on the sun’s surface with the amount of energy they put out. “This instrument will not only tell us where the sources of solar variation come from, but give us some idea of how they might have varied in the past,” Rust says.

He adds that the team would like to perform additional tests on the telescope, perhaps a two to four-week flight that would allow it to capture a full rotation of the sun. Once the technology is further fine-tuned, they plan to propose it for a NASA Small Explorers mission.