Hydrogen Alpha Emissions
Some important terms to define here is the
Nanometer and the Angstrom. A nanometer (nm) is one-billionth of a meter
and an Angstrom (Å) is one tenth of that (on the order on the size of an
atom). This is the type of tolerances we are talking about with Ha
filters.
Zooming in on the red portion of the visible spectrum you see the
specific Ha emission line. Ha filters are rated by their bandwidth or
how much of the spectrum they cover near the Ha emission line.
A filter with a bandwidth of 2Å may only show prominences but a 1Å
filter (which is considered narowband) will show prominences and surface
detail. Some filters now go down to as low as .1Å. The narrower the
bandwidth, the more contrast disk detail tends to have but the higher
the price.
The "Wings" of Hydrogen-Alpha
The profile of the H-alpha line is a little like a bell-shaped curve
rather than just a narrow line of zero width. H-alpha has a certain
width due to physical processes going on the sun. The "wings" of H-alpha
are the edges of this profile off the centerline wavelength. 6562.8
Angstroms is the so-called "centerline" (the middle of the spectral
line's profile) and is where the filter should be tuned to generally.
Wavelengths which are off the precise centerline wavelength on the
longer wavelength side of 6562.8 Angstroms are referred to as being in
the "red wing", while wavelengths towards the blue side of the center
line wavelength are in the "blue wing". The "wings" of solar H-alpha
emission are nearly one angstrom wide, although usually we observe
something like 0.7 Angstroms off the peak when we are looking in "the
wings". Much farther off the peak than 1 Angstrom and we often see
nothing but white-light detail (unless it is material from a really
energetic solar flare, which can be a couple of Angstroms off).
Why Ha? |
The View |
What you see |
The Chromos |
Ha Emission |
Bandwidth |
Main Designs |
Ha Components |
Rear Filters |
The Etalon |
Front Filters |
Coronado filters |
DayStar Filters |
Solar Spectrum Filters
