New solar telescope offers crystal clear view of sun's surface

A new 1.6-metre clear aperture solar telescope - the largest of its kind in the world - has seen 'first scientific light:' it's now operational. The unveiling of the instrument, cited as the pathfinder for future, large ground-based telescopes, could not have come at a more auspicious moment, scientists say. This year marks the 400th anniversary of Galileo's telescope, used to demonstrate that sunspots are indeed located on the Sun.

'With our new instrument, Galileo's work can leap ahead with a capability never before available,' says physicist Philip Goode of the New Jersey Institute of Technology in Newark, N.J.

Goode has been director of Big Bear Solar Observatory (BBSO), since NJIT took over management of BBSO in 1997 from the California Institute of Technology. The new solar telescope is located at the BBSO, high above sea-level in Big Bear Lake, Calif.

The National Science Foundation (NSF), Air Force Office of Special Research (AFOSR) and NASA provided more than $5 million in components.

'The new solar telescope will be the premier ground-based instrument in the U.S. for high-resolution observations of the sun,' said Paul Bellaire, program director in NSF's Division of Atmospheric Sciences. 'The sun is the source of all 'space weather' that ultimately affects Earth in solar storms.'

With the telescope, scientists are seeing images 'that offer a much better understanding of the sun,' said Goode. 'Through this instrument, we will have a new look at the sun's dynamic storms and space weather, which can have dramatic effects on Earth.'

'Our prized first image shows the sun's ever-present, turbulent 'granular field,' with the largest granules about the size of Alaska,' says Goode. 'The small, bright points against a dark background are the smallest-scale magnetic structures on the sun.'

If one looks closely, he says, a string of pearls becomes visible. 'Each pearl is a cross-section of an intense, single fibre of the sun's magnetic field - the basic building block of solar magnetism.'

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 says.

The instrument represents a significant advance in high-resolution observations of the sun, with the largest aperture of any solar telescope in existence, said Goode.

Other pluses include its location - high atop a California mountain. It's called an off-axis instrument; no part of the sun's light is blocked by the telescope itself.

The telescope will be used in joint observation campaigns with NASA satellites to optimise the study of solar observations.

A 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 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. After a day of observations, the mirror must be cooled overnight to ensure that it is chillier than ambient air temperature by morning. With dawn comes the start of a new day of doing what the human eye cannot: looking directly at the sun.

'The telescope's 'first light,'' says Goode, 'was a defining moment.'