Bandwidth of Hydrogen Alpha
Filters
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
