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World's largest solar telescope now operational

The New Jersey Institute of Technology's 1.6-meter instrument will be used in conjunction with NASA satellites to optimize the scientific output of Sun observations.
Provided by the New Jersey Institute of Technology, Newark
Big Bear Solar Observatory
The New Jersey Institute of Technology's new 1.6-meter clear aperature solar telescope is now operational at the Big Bear Solar Observatory in Big Bear Lake, California.
Big Bear Solar Observatory
May 29, 2009
The New Jersey Institute of Technology's (NJIT) new 1.6-meter clear aperture solar telescope — the largest of its kind in the world — is now operational. The unveiling of this instrument — said to be the pathfinder for all future, large ground-based telescopes — comes as the astronomical community celebrates the 400th anniversary of Galileo using his telescope to demonstrate that sunspots exist.

"With our new big, beautiful white machine, Galileo's work can leap ahead with a capability never before available," said NJIT Distinguished Professor of Physics Philip R. Goode. Goode has been director of Big Bear Solar Observatory (BBSO) in Big Bear Lake, California, since NJIT took over management of BBSO in 1997 from California Institute of Technology. Located high above sea level, the observatory is one of the premier land-based facilities supported by federal funding.

"We are already seeing images offering a better understanding of the Sun," said Goode. "With this instrument, we should be able to have a better understanding of dynamic storms and space weather, which can have dramatic effects on Earth."

Earlier this month, researchers achieved what is called first scientific light. This means the telescope is operational. To achieve its full powers, at least 3 more years of work will be needed to bring online evermore sophisticated hardware for observing the Sun.

Nevertheless, Goode and the BBSO research team were able to extract a few unique images. Photos clearly illustrate the before-and-after capabilities of the old versus new telescope. "Our prized first image shows the Sun's ever-present, turbulent granular field with its largest granules being about the size of Alaska," Goode said.

Goode adds that the Sun is now in a state of prolonged magnetic inactivity, perhaps the longest such time in a century. "The new telescope is ideal for studying the Sun as it rises from this strange state of quietude," he added.

The new instrument has 3 times the aperture of the old telescope. It represents a significant advance in high-resolution observations of the Sun because it has the largest aperture of any solar telescope in existence, said Goode. Since it is an off-axis telescope, it doesn't block any part of the sunlight. Other positives include its location — high next to a Southern California mountain lake.

The new telescope will be used in joint observation campaigns with NASA satellites to optimize the scientific output of all observations of the Sun. BBSO has always operated in such campaigns, but now it can do so with greatly enhanced capabilities. The National Science Foundation (NSF), Air Force Office of Scientific Research (AFOSR) and NASA have provided more than $5 million in hardware components.

The telescope is filled with new technologies. World-renowned Steward Observatory Mirror Laboratory at the University of Arizona (UA) polished the 1.7-meter (just shy of 6 feet) primary mirror. The extremely precise measurements of the mirror's shape required the application, for the first time, of a computer-generated hologram. The development of this technology will be essential for figuring the next generation of even-larger nighttime telescopes. The final error in the primary mirror is only a few parts in a billion from its desired parabolic shape. "Buddy Martin at the UA Mirror Lab has described the mirror as the pathfinder for large nighttime telescopes that are about to be built," said Goode.

Another key design issue for this large-aperture solar telescope was the creation of a thermal control system capable of maintaining the temperature of the mirrors near or below ambient air. To achieve this, the dome employs a wind-gate and exhaust system that controls the airflow from the wind.

The structure maintains the same temperature inside and outside the dome and clears concentrations of heat in and around the optical paths. In addition, BBSO engineers implemented a closed-cycle, chilled-air system as part of the telescope mount to limit so-called "mirror seeing." This sweeps away turbulent cells and directly cools the primary mirror. After a day of observations, the mirror must be cooled overnight to ensure that it is somewhat cooler than ambient in the morning.

DFM Engineering of Longmont, Colorado, built and tested the optical support structure and active-support mirror cell for the enormous mirror. It is supported by 36 actuators that can bend out low-order aberrations, such as those due to gravity and/or thermal effects.

The telescope is now in its commissioning phase, in which more sophisticated observations are made possible with the implementation of advanced hardware. These include adaptive optics to correct for atmospheric distortion and hardware to measure magnetic fields in visible and infrared light.

"It is good at last to have our destiny in our own hands rather than those of our capable partners," said Goode. "Seeing first light was a great moment because the team in BBSO finally knew that its big white machine works as we had planned."
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