dynamic top surface “ chromosphere ” get washed out due to the much brighter underlying “ photosphere ” layer . Here comes the role of the H-Alpha system .
What is H-Alpha ? As we know , following particle physics rules , every element influences electromagnetic waves of a specific wavelength thus a specific portion of spectrum . If we break and study sunlight into a spectrum through a spectroscope , we find many definite dark lines in the multicolour band due to the absence of a few particular colours or lights of particular wavelengths in it . These dark lines are caused by elements that absorb the lights of those particular wavelengths . The most prominent one among them is caused by absorption or influence of hydrogen . That portion of the spectrum at the wavelength of 6562.8 Angstroms is commonly known as H-Alpha . The Sun ’ s top surface or chromosphere greatly influences this particular portion of spectrum as it is actually a layer of glowing hydrogen gas . Naturally , if we can see Sun only through the H-Alpha
portion of spectrum by eliminating all other lights , we will be able to ‘ see ’ disturbances , influences or details of the chromosphere . But to do that , instead of simple filtering we need a system that at first can attenuate sunlight to a safe level , then block all colours of spectrum while allowing a very narrow portion or band of that only to pass . To work properly , this bandpass needs to be only 0.7 Å wide centered at Hydrogen Alpha spectral line ( 6562.8 Å ). A time tasted method of doing this is by using a spectrohelioscope . But that is too complicated a system to be used by a common enthusiasts . The other and more common method is an H-Alpha system that allows a band pass of 0.5 to 1.0 Å centering at 6562.8 Å .
What are the main sections of an H Alpha system ? Energy Reduction Filter ( ERF ) Fabry-Perot Etalon Blocking filter ( BF )
COURTESY OF Debasis Sarkar and Janmejoy Sarkar . ( Sky Watchers Association of North Bengal )
Solar transit of International Space Station in H-Alpha ( India ’ s first H-Alpha ISS Solar Transit image )
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