The Sun in H-a Light... At Last!
On Friday, August 9, 1996, I unpacked a Lumicon 1.5A Hydrogen-alpha filter.
I've wanted a filter like this for thirty years and as I thought that
was enough time to have wasted, I immediately improvised some hardware with
which to try it out.
Saturday morning, using a 3-inch Unitron refractor and the
full 77mm aperture of the standard
energy-rejection filter, I found this hedge-row prominence suspended over
the fuzzy limb of the sun. The F16 focal ratio is a little too fast for
the 1.5A filter (Lumicon recommends at least F20). I tried the filter on
a couple of other telescopes and decided that a 5-inch F6 A-P refractor
showed the most promise when masked down and used with a 2-inch Barlow to
get very near the recommended focal ratio. When some high clouds drifted
through, I retreated indoors to make improved filter brackets, scribble
notes, smear aloe-vera on my sunburn, and wait for the sky to clear. I
also scattered a lot of excited email throughout the northern hemisphere.
[1996 August 10, 11:00 EDT]
I rigged the 5-inch A-P refractor to operate in H-a at F24. An up-ended
Maxwell House coffee can is involved, as is lots of black paint; I picked
the F24 focal ratio because the biggest hole saw I have cuts a circle
63mm in diameter. Much better contrast now! The "fuzzy" limb of the sun
turned out to be the chromosphere, complete with fine "spicules" and
miniature prominence "wannabe's." Sacchi's "burning prairie" was easy to
see despite lively afternoon air and makes a good "tuning target".
During this season of the quiet sun, it seems likely there'll be days when
no prominences are visible. At such times, this visible layer of glowing
hydrogen will let me know when the filter is tuned properly. After seven
hours, all that's left of this morning's prominence are these two
towers. [1996 August 10, 18:00 EDT]
On Sunday morning, thunderstorms moved in, but through clear "leads"
between oncoming clouds I enjoyed clear views of the sun. In these two
views, the leading western limb of the sun is at the top and north
is to the left. On the leading edge were two prominences. Did I really
see changes in one prominence yesterday or did I see one in the morning and
the other in the afternoon? One of today's leading edge prominences reminded
me of a tree (tens of thousands of miles high, but a lone cypress just the
same) and the other of smoke blowing from an unlikely stack. This second
prominence was just a sheet of glowing gas hovering above the limb, showing
some intermittant detail especially with the telescope in motion. Is this
coronal rain? Fainter sheets seemed to hover between the two prominences.
[1996 August 11, 11:30 EDT]
This large deformed loop rises above the southern trailing limb -- while
experimenting to find the best arrangement of filter, Barlow, and star
diagonal, I overlooked this one and only noticed it when I went back to
yesterday's arrangement. (My preferred optical train is: rejection filter,
objective, diagonal, Barlow, filter, then eyepiece; the alternative with
the Barlow and filter "upstream" of the diagonal yields higher magnification,
a shakier extension of the focusser, and lower contrast). The word for
my impression of today prominences is "smokey". A modest group of sunspots
is about a day past the solar meridian -- this should bode well for good
prominence viewing next weekend. No Perseids for me tonight: rain instead.
[1996 August 11, 11:30 EDT]
Later that same week...Tuesday
Take me home!