The sun’s disk showing active region 10486, which became the largest sunspot seen by SOHO, the satellite Dr. Kuhn and collaborators used to monitor the sun’s diameter. Courtesy of SOHO/MDI consortium. SOHO is a project of international cooperation between ESA and NASA.
A group of astronomers led by the University of Hawaii’s Dr. Jeff Kuhn has found that in recent times the sun’s size has been remarkably constant. Its diameter has changed by less than one part in a million over the last 12 years.
“This constancy is baffling, given the violence of the changes we see every day on the sun’s surface and the fluctuations that take place over an 11-year solar cycle,” commented Kuhn, the associate director of the University of Hawaii Institute for Astronomy (IfA) who is responsible for Haleakala Observatories.
Kuhn’s work is part of worldwide efforts to understand the influence of the sun on Earth’s climate. “We can’t predict the climate on Earth until we understand these changes on the sun,” he said.
Kuhn and his colleagues (Dr. Rock Bush from Stanford, Dr. Marcelo Emilio from Brazil, and Dr. Isabelle Scholl at IfA) used NASA’s long-lived Solar and Heliospheric Observatory (SOHO) satellite to monitor the sun’s diameter, and they will soon repeat the experiment with much greater accuracy using NASA’s new Solar Dynamics Observatory (SDO), which was launched on February 11. According to Kuhn, the ultimate solution to this puzzle will depend on probing the smallest observable scales of the solar surface using the Advanced Technology Solar Telescope (ATST), which is scheduled for completion on Haleakala in 2017.
“To be able to predict what the sun will do, we need both the big picture and the details,” said Kuhn. “Just as powerful hurricanes on Earth start as a gentle breeze, the analogs of terrestrial storms on the sun start as small kinks in the sun’s magnetic field.”
Founded in 1967, the Institute for Astronomy at the University of Hawaii at Manoa conducts
research into galaxies, cosmology, stars, planets, and the
sun. Its faculty and staff are also involved in astronomy education,
deep space missions, and in the development and management
of the observatories on Haleakala and Mauna Kea.
Established in 1907 and fully accredited by the Western Association
of Schools and Colleges, the University of Hawaii is the state's
sole public system of higher education. The UH System provides
an array of undergraduate, graduate, and professional degrees
and community programs on 10 campuses and through educational,
training, and research centers across the state. UH enrolls
more than 50,000 students from Hawaii, the U.S. mainland, and
around the world.