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What can be expected with solar filters?



 
 
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  #1  
Old July 16th 03, 02:49 AM
Rune Allnor
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Default What can be expected with solar filters?

Hi all.

After geting strong advice from s.a.a not to risk the telscope and
eyepice on solar projection, I would like to check out solar filters
to be mounted in front of the telescope objective.

From what I understand, there are at least two types of filters.
The first is one that merely reduces the amount of light that enters
the telescope. The example pictures I have seen essentially show the
solar disc with some sun spots. Some people I have talked to, said
that these types of filters were very popular (in terms of sold units)
just before eclipses.

Now, we just had an eclipse a couple of months ago, and I don't know
when the next is to be expected. I have seen some mentioning of
"Hydrogen Alpha" filters, that only let specific parts of the hydrogen
spectrum through. There is some vague mentioning of these filters
being "expensive!", but, on the other hand, there may be way more detail
to be seen on the sun than with the more ordinary filters. The prospect
of watching the sun almost every day, to get an impression of the
dynamics of the sun, does have a stronger appeal to me than merely
having a quick look every eclipse or so.

All of this put the following questions to mind:

- What types of details can one expect to see with Hydrogen Alpha
filters that don't appear with the "ordinary" filters? I have the
impression protuberances and surface granularity would be visible.
What about flares? Other details? Would one see dynamic features
i.e. instant movement on the surface as opposed to sunspot positions
that change over hours and days?

The telescope in question is of 80 mm aperture with a 20-60x eyepiece.

- How much more expensive are the Hydrogen Alpha filters than ordinary
ones? 2 times? 10 times?

Any opinions much appreciated.

Rune
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  #2  
Old July 16th 03, 06:35 AM
David Knisely
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Default What can be expected with solar filters?

Hi there. You posted:

What types of details can one expect to see with Hydrogen Alpha
filters that don't appear with the "ordinary" filters? I have the
impression protuberances and surface granularity would be visible.
What about flares? Other details? Would one see dynamic features
i.e. instant movement on the surface as opposed to sunspot positions
that change over hours and days?


There is a *huge* difference between the views in white light (ie:
ordinary broad-band solar filters) and those in a sub-angstrom H-alpha
filter (passband of less than one Angstrom in width). In white light,
you can see sunspots and some brighter patches on the disk toward the
limb known as faculae, but that's about it. Its fun to watch and
relatively inexpensive, so white-light filters are pretty popular.
However, in H-alpha, you are viewing the thin layer of the sun's
atmosphere known as the Chromosphere. On the limb, you will see the
gigantic streamers of gas known as prominences while, on the disk, the
prominences become dark and are known as "filaments". You will also see
a mass of fine fibril detail on the disk, as well as brighter patches
known as "plage" seen around active regions. Sunspots can be visible as
well, but there is a great deal of detail around them which is not
visible in white light filters. The surface is in almost constant
turmoil and with careful study, small-scale changes can easily be
noticed in only a few minutes. Solar flares are visible in H-alpha
filters as well (not usually seen in white light), and some move quite
rapidly so that you can actually see things move in a few minutes time.
I have seen some solar flares erupt in only a few *seconds* of time, and
they are a lot of fun to watch. Some of these events are quite
spectacular, so the views you may have seen in some H-alpha movies are
not far off from what is seen viewing with the eye. If you want to
compare the view in H-alpha to that of white light, go to the web page
of Big Bear Solar Observatory http://www.bbso.njit.edu and click on the
"Latest Images". They also have "live" images in H-alpha which are
updated every few minutes when the sun is up over Big Bear, California.

The telescope in question is of 80 mm aperture with a 20-60x eyepiece.

- How much more expensive are the Hydrogen Alpha filters than ordinary
ones? 2 times? 10 times?


A good 80mm "white light" solar filter might run you something like $40
to $60 and is well worth the money. An H-alpha filter with an 80mm
aperture will run you considerably more than this even if you use one
which is quite small like the SolarMax 40mm model, which is around
$1250. There are two companies which currently market decent H-alpha
filters (ie: those with bandwidths of less than one Angstrom, which is
required to see much on the disk). These are DayStar Filters and
Coronado. The DayStar filters can be somewhat less expensive, but
require *long* focal length telescopes to work properly (f/ratios of
f/30 or longer). The least expensive of the DayStar line of filters
(the T-Scanner) starts at around $1600, not including the energy
rejection filter which has to be mounted in front of the objective. I
have used my T-Scanner for about 17 years and I really enjoy it. The
Coronado filters are a bit simpler and will work at almost any focal
length, although again, if you want any significant aperture, the price
is rather high (their 60mm model is over $2500 and their 90mm aperture
model is over $5000). These filters also take a while to make, so if
you are considering getting an H-alpha filter, be prepared for a wait
which can last months.
For those who are interested solar observing in Hydrogen-alpha light,
check out the on-line publication: OBSERVING THE SUN IN H-ALPHA,
available on the Web page of the Prairie Astronomy Club:
http://www.prairieastronomyclub.org It is a guide containing a useful
intoduction to observing equipment and techniques, coupled with a
comprehensive look at the terminology and behavior of solar H-alpha
features which the amateur might see. The information was compiled from
the text ASTROPHYSICS OF THE SUN by Harold Zirin (Cal. Tech), and
provides a review of features such as Prominences H-alpha disk detail,
H-alpha sunspot development and behavior, solar activity, and solar
flares. The guide also contains a glossary of the most common H-alpha
terms used by
many observers.
For those who do not have H-alpha equipment but still want to follow
the sun's activity, these web sites provide quality images and
information.

"EYES ON THE SKIES" ROBOTIC SOLAR TELESCOPE OBSERVATORY:
http://sunmil1.uml.edu/eyes/index.html
This site is run by amateur astronomer Mike Rushford, and produces
"Live" H-alpha images with a small solar scope and a sub-angstrom
filter. The scope produces medium to high resolution images, and can be
moved by the user, with changable image parameters. Since it is only
one site (California), there will be times when no images will be
present due to weather conditions. There is also a limited archive of
interesting movies and images of H-alpha solar activity. In addition,
an extensive solar observing FAQ is provided, covering equipment and
some solar terms.

Astro-USON WebTV Observatorio "CarlSagan" (Sonora, Mexico)
http://cosmos.astro.uson.mx/webtv/webtv.htm
Live high-resolution (754x487 pixels) images from a 125 mm aperture f/10
Catadioptric telescope using a 0.6 Angstrom H-alpha filter are provided
from this Mexican site, including occasional longer exposures on the
limb to provide better coverage of limb prominences and activity (it is
helpful if you can read Spanish, although you can still get around
without knowing the language). The schedule is Monday through Saturday
from 15 hrs to 22 hrs UTC weather permitting.

BIG BEAR SOLAR OBSERVATORY (BBSO) http://www.bbso.njit.edu/
Big Bear provides high resolution (up to 2024 x 2024 pixels) full-disk
images of the sun in both white light and H-alpha, along with current
information on solar activity. They also provide their "live" moderate
resolution images (updated about every minute) along with a plot of
current
solar X-ray emission. However, since this is only one observatory, and
is mainly a research facility, there will be times when images will not
be updated due to weather conditions or research projects. In addition,
Big Bear is part of the Global H-alpha Newtwork, so at least a few
images may be available when the sun is not up over Big Bear. They
provide a wealth
of information concerning active region history, location, type, and
current level of activity, which is very useful for keeping track of
things when you can't observe every day. Big Bear also has an extensive
archive of images and movies (including a "daily movie" when it was
clear at the
observatory) which demonstrate some interesting solar phenomenon.

NATIONAL SOLAR ASTRONOMY OBSERVATORY http://www.sunspot.noao.edu/
This site provides "near-live" full-disk medium resolution images of the
sun in H-alpha updated every few minutes, and solar images in Calcium
and white light every ten minutes from the National Solar Astronomy
Observatory at Sunspot, New Mexico. These images are of somewhat higher
resolution than those from the Space Environment Laboratory, but are not
as high as those from sites like BBSO or the "Eyes on the Skies"
telescope. In addition, archived images and movies of solar activity
are available, along with information on solar activity and useful
links.

SPACE ENVIRONMENT CENTER http://www.sel.noaa.gov/
This site is probably the best one for complete information on current
and future solar/terrestrial conditions and activity. They provide
lower-resolution "colorized" full-disk H-alpha images several times per
day from observing sites in New Mexico and Australia, along with
selected higher resolution active region images. There is also an
extensive archive of past images and information, along with a glossary
of solar terms.

Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club:
http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************
  #3  
Old July 16th 03, 03:28 PM
Al
external usenet poster
 
Posts: n/a
Default What can be expected with solar filters?



Hi all.

After geting strong advice from s.a.a not to risk the telscope and
eyepice on solar projection, I would like to check out solar filters
to be mounted in front of the telescope objective.

[snip]

All of this put the following questions to mind:

- What types of details can one expect to see with Hydrogen Alpha
filters that don't appear with the "ordinary" filters? I have the
impression protuberances and surface granularity would be visible.
What about flares? Other details? Would one see dynamic features
i.e. instant movement on the surface as opposed to sunspot positions
that change over hours and days?

The telescope in question is of 80 mm aperture with a 20-60x eyepiece.

- How much more expensive are the Hydrogen Alpha filters than ordinary
ones? 2 times? 10 times?

Any opinions much appreciated.

Rune


I agree with everything you've been told so far regarding the wonders
visible with an H-alpha filter such as the Coronado...it's all true.
However, there are a few things you have not been told, which are not
terrible, but will give you a more accurate picture of using the H-alpha...

I own a 60mm Coronado, which I purchased this year. The first time I used
it, I nearly jumped out of my skin. After the novelty wore off, I began to
see some of the downsides of this expensive toy. I use my H-alpha with a TV
Pronto scope having a focal length of under 500mm. (Unless you change part
of the filter, you are limited to using the H-alpha with a scope no greater
than 1,000mm. If you prefer to use the filter with a longer focal length,
it would cost $1,500 (about) to buy that part of the filter which would
allow you to do so.) With a 10mm eyepiece, the disc of the sun is
completely in the field of view, so all activity on the sun is minute in
size, as compared to the disc of the sun. In other words, the activity that
you want to see appears as _very_ small. BTW, using a barlow between the
telescope and the eyepiece does not help the quality of the image and for
this reason I keep away from the barlow. On the other hand, a CCD or even a
good digital camera allows you to see _much_ more...unfortunately, not in
real time.

The other thing you should understand is that the level of solar activity is
not constant. There are days when you can view for hours and see almost
nothing...because nothing big is happening. During the period of time that
I've owned the H-alpha (about 5 months), I had only one day of viewing that
I would consider spectacular. Keep in mind that I live in the Northeast,
where we've had an absolutely disasterous spring and early summer. Believe
it or not, during the past 5 months, clouds covered the Northeast at least
85% of the time. During the past 3 weeks or more, doing any solar viewing
while temperatures hovered in the area of 100 degrees was out of the
question.

So, before you part with the bucks to buy one of this filters, keep the
above in mind. Keep in mind also that I am no authority on H-alpha filters.
What I say here are only my early feelings. It's quite possible that with
more experience I may change my mind completely. Finally, in spite of what
I said above, the H-alpha, while not perfect in my mind, is still quite
fantastic!

Al



  #4  
Old July 16th 03, 07:33 PM
David Knisely
external usenet poster
 
Posts: n/a
Default What can be expected with solar filters?

Hi there. You posted:

Question: Back in the late 60s/early 70s S&T ran some articles on ATM
built H-alpha filters, that seemed to provide good results. The
technology was different than current commercial products, but
sub-angstrom imaging was claimed. Can anyone point me at current
home-built H-alpha filter information and/or web sites?


Well, AMATEUR TELESCOPE MAKING Book III (original edition) has some
information on such filters using optical activity in certain crystal
substances, but as I recall, it was very difficult to get the materials
and the bandwidths weren't quite as good as the filters which used
Fabry-Perot Etalons. The other method cited in Sky and Telescope was
the Spectrohelioscope, which is essentually a "scanning" spectroscope
set on the H-alpha line. It worked, but had a limited field of view.
One guy I saw at an Astronomical League convention had one, and I asked
him about it. He said that the DayStar filters like the one I had
worked better, but since the sky was cloudy, I was unable to judge for
myself. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club:
http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************
  #5  
Old July 17th 03, 02:48 PM
Kevin Smith
external usenet poster
 
Posts: n/a
Default What can be expected with solar filters?


If you are interested with what you can do with a little bit of focal
length, and a lot of DayStar Filter have a look at a small bit of my web
site. WIth a 5" ERF, and a 0.7 ATM from Daystar a huge amount of detail can
be collected.

The link is

http://www.users.globalnet.co.uk/~ke...res%20Images.h
tml

I also have some images with a 0.5 ATM at

http://www.users.globalnet.co.uk/~ke...5%20burst.html

and

http://www.users.globalnet.co.uk/~ke...h%20June%20200
3.html

Get back to me off group if I can be of any further help.

Kevin
www.kevsmith.com
www.siriusobservatoriesuk.com
DayStar Filters UK

So, before you part with the bucks to buy one of this filters, keep the
above in mind. Keep in mind also that I am no authority on H-alpha

filters.
What I say here are only my early feelings. It's quite possible that with
more experience I may change my mind completely. Finally, in spite of

what
I said above, the H-alpha, while not perfect in my mind, is still quite
fantastic!

Al





 




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