RHESSI first light
Credit: NASA

Footprints of Fire: Dancing in the Circle of Light

The Sun is mysteriously active. Huge storms and explosions beseige the sun's surface; giant structures larger than earth form and dissolve in the space of days, sometimes minutes. On the most recent Sun-Earth Day,on March 20, 2002, astronomers had a brand-new tool to use in the study of these titanic forces: the Reuven Ramaty High-Energy Solar Spectroscopic Imager, or RHESSI. RHESSI is a satellite designed to study the high energy X-ray and Gamma-Ray emissions generated by solar storms and solar flares. The image above shows one of the first images obtained by RHESSI, of a modest solar flare (only as powerful as a million megatons of TNT) which occurred on February 20. The image above emphasizes the power of RHESSI: it can spatially resolve the sources of the flare emission, and can also measure differences in the energy spectrum of the emission too. In the above image the inset shows a peanut-shaped flare region made up of 2 flare "footpoints" located near the solar surface connected by a bridge of higher emission. The solid lines represent the spectrum of energy from the spatially distinct regions. The footpoints have similar spectra and are probably produced by electrons accelerated to about 50% of the speed of light; the emission between the footpoints is probably produced by gas heated to temperatures of millions of degrees by the flare.

RHESSI was launched in February and was recently renamed in honor of Dr. Reuven Ramaty, who died in 2001 after a long and distinguished career in the Laboratory for High Energy Astrophysics at the NASA Goddard Space Flight Center, Greenbelt, Md. Ramaty was a pioneer in the field of solar-flare physics, gamma-ray astronomy and cosmic rays.

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Page Author: Dr. Michael F. Corcoran
Last modified March 24, 2002