This solar blink-sequence allows direct comparison of dramatic variations occurring simultaneously in the Hydrogen-alpha and white-light bands. It is particularly interesting that while the white-light image indicates minimal sunspot activity, the H-a components are exceedingly active.Massive filaments course prominently above the surface, invisible to white-light and deep-density filters.
White-light filters allow us to view features of the bright portion usually thought of as the sun's "surface", while H-a filters, rejecting all but a very narrow slice of the spectrum, allow us to see activity otherwise overwhelmed by the intensely bright Photosphere lying below. It's not unlike the blinding light from a high-beam headlamp which prevents seeing the faint lettering on the bulb, but an H-a filter, like a pair of magic glasses, removes that bright background Photosphere and allows only the signal of interest to pass.
The H-a filter used here is designed to pass a signal at 6562.8 Angstrom... the first spectral band of Hydrogen activity, or more commonly refered to as Hydrogen-alpha. The bandwidth is also very tightly controlled at <0.7 Angstrom, so as to provide high contrast. Moving too tightly though can diminish the fullness of the prominences, as they tend to spill across wider frequency ranges. To put the level of precision in perpsective, 1 angstrom is one hundred-millionth of a centimeter!
This was a collaborative effort, with Luis Carreira of Portugal providing the white-light image. You can view the full-scale version of the white-light image and much more on his solar imaging web-site. |
