Stanford's solar observer sees the sun in high definition

By Gwyneth Dickey

Fiery images of the sun showing magnetic storms and deafening sound waves are are now beaming back to Earth, thanks to a recently launched solar telescope developed by Stanford scientists. The Helioseismic and Magnetic Imager (HMI) is one of three instruments aboard NASA's Solar Dynamics Observatory (SDO) satellite that will help forecasters learn to predict dangerous solar events in the future.

"We're really excited," said physicist Phil Scherrer from Stanford's physics department, the principal investigator on the project. "The images are everything we hoped for."

SDO was launched into space on Feb. 11. After weeks of spacecraft testing instrument calibration, it now orbits 22,500 miles above Earth, taking high-resolution images 10 times better than high-definition television. For at least five years, it will send 1.5 terabytes of data back to Earth every day, equivalent to a download of half a million songs onto an MP3 player.

Scherrer and a core team of scientists unveiled the first images at a NASA press conference held Wednesday at the Newseum in Washington, D.C.

"After eight years of building it, we're ready to get the data we can use for doing science," said Scherrer, who is affiliated with Stanford's Center for Space Science and Astrophysics, and the Hansen Experimental Physics Laboratory.

Violent solar activity has been known to interfere with technology here on Earth. Radio communication, navigation devices, power grids and cell phones are vulnerable to solar flares and storms, as are astronauts and instruments in space. Using SDO's instruments, scientists will learn to predict dangerous space weather to better warn and protect against such disruptions.

The HMI, designed and built by a team from Stanford and Lockheed Martin’s Solar and Astrophysics Laboratory in Palo Alto, Calif., measures the sun's magnetic fields and the motions caused by sound waves. It measures subtle shifts in the color of light absorbed by iron in the sun's atmosphere. The color changes depending on the strength of the magnetic fields and how fast the surface rises and falls.  For instance, if the color is bluer, that part of the surface is bubbling outward, and if it turns a little red, it's falling back down.

This surface motion is caused by sound waves generated by hot, bubbling gases reverberating inside the sun. Variation in the magnetic fields created by deeper motions can lead to solar events. By measuring the speed and direction along the waves' paths, scientists can infer what's going on all the way through to the far side of the sun, and they hope to be able to identify precursor events that warn of dangerous solar storms.

SDO is being called the "Hubble of heliophysics," said NASA scientist Madhulika Guhathakurta, and is expected to do for heliophysics what the Hubble telescope did for astrophysics and cosmology. Scientists are already reevaluating existing theories about solar dynamics and coming up with new ones to explain what they've observed with SDO.

Two other SDO instruments gather slightly different solar data. The first, the Atmospheric Imaging Assembly, is a set of four telescopes designed to photograph activity in the sun’s atmosphere. The instrument measures 10 different colors of ultraviolet light, selected to reveal just how solar activity energizes the corona. These whole-sun images will show details never seen before by scientists. The principal investigator is Alan Title of the Lockheed Martin laboratory, which built the instrument.

The other instrument, the Extreme Ultraviolet Variability Experiment, measures total change in the sun’s radiant emissions. These emissions have a direct and powerful effect on Earth’s upper atmosphere – heating it, puffing it up, and breaking apart atoms and molecules. Researchers don’t know how fast the sun can vary at many of these wavelengths, so they expect to make discoveries about flare events. The principal investigator is Tom Woods of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. LASP built the instrument.

Taken together, data from SDO’s three instruments are even more powerful for understanding the sun’s complex activity. SDO is the first mission of NASA's Living with a Star Program, or LWS, and the crown jewel in a fleet of NASA missions to study our sun and space environment. The goal of LWS is to develop the scientific understanding necessary to address those aspects of the connected sun-Earth system that directly affect life and society.

Gwyneth Dickey is an intern with the Stanford News Service.

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