Viewing the sun, Chapter 2

Thanks to all who replied to my earlier post about viewing the sun.

So, this afternoon the ETX-90 and I tried again. Put the solar filter on
the scope, stuck in a 40mm Plossl (31X), capped the finder scope, aligned
the ETX-90, and told it to GOTO the sun. In the ETX-90 Autostar controller,
the sun is listed under Asteroids -- go to the asteroid menu and keep
scrolling until you find Sun and there it is. Scope slewed to the sun, I
used the arrow buttons to adjust it, watching the shadow of the scope --
amazing -- watching the shadow is a great way to aim the scope.

In the 40mm EP I could detect two tiny sunspots but the FOV was too much --
I have to keep looking around the inside of the EP to see the sun. 26mm
(48X) and 12.4mm (101X) seemed to give the best views. I was trying to see
eruptions from the edge of the sun but never could -- went to a 6.4mm (195X)
Plossl and still could not see anything flaming off the edge of the sun's
disk -- am I expecting too much?

Tomorrow I plan to use my 5mm Nagler to see what that shows. Still, the
sunspots were clearly visible and I'm glad I have figured out how to locate
the sun using the "scope-shadow" method.

--

----
Joe S.

I was trying to see
eruptions from the edge of the sun but never could

In order to see these (prominences) you need
a very narrow band filter called an H-alpha
filter, which transmits light of a single
spectral line in the red at 6563 angstroms.
These are *very* expensive.

Unless you buy a Hydrogen-alpha filter, all you'll ever see is sunspots,
unless you get lucky enough to be on a path of totality for a total solar
eclipse...
Orion


"Joe S." wrote in message
...
Thanks to all who replied to my earlier post about viewing the sun.

So, this afternoon the ETX-90 and I tried again. Put the solar filter on
the scope, stuck in a 40mm Plossl (31X), capped the finder scope, aligned
the ETX-90, and told it to GOTO the sun. In the ETX-90 Autostar
controller,
the sun is listed under Asteroids -- go to the asteroid menu and keep
scrolling until you find Sun and there it is. Scope slewed to the sun, I
used the arrow buttons to adjust it, watching the shadow of the scope --
amazing -- watching the shadow is a great way to aim the scope.

In the 40mm EP I could detect two tiny sunspots but the FOV was too
much --
I have to keep looking around the inside of the EP to see the sun. 26mm
(48X) and 12.4mm (101X) seemed to give the best views. I was trying to
see
eruptions from the edge of the sun but never could -- went to a 6.4mm
(195X)
Plossl and still could not see anything flaming off the edge of the sun's
disk -- am I expecting too much?

Tomorrow I plan to use my 5mm Nagler to see what that shows. Still, the
sunspots were clearly visible and I'm glad I have figured out how to
locate
the sun using the "scope-shadow" method.

--

----
Joe S.




---
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"Joe S." wrote in message
...
Thanks to all who replied to my earlier post about viewing the sun.

So, this afternoon the ETX-90 and I tried again. Put the solar filter on
the scope, stuck in a 40mm Plossl (31X), capped the finder scope, aligned
the ETX-90, and told it to GOTO the sun. In the ETX-90 Autostar
controller,
the sun is listed under Asteroids -- go to the asteroid menu and keep
scrolling until you find Sun and there it is. Scope slewed to the sun, I
used the arrow buttons to adjust it, watching the shadow of the scope --
amazing -- watching the shadow is a great way to aim the scope.

In the 40mm EP I could detect two tiny sunspots but the FOV was too
much --
I have to keep looking around the inside of the EP to see the sun. 26mm
(48X) and 12.4mm (101X) seemed to give the best views. I was trying to
see
eruptions from the edge of the sun but never could -- went to a 6.4mm
(195X)
Plossl and still could not see anything flaming off the edge of the sun's
disk -- am I expecting too much?

Tomorrow I plan to use my 5mm Nagler to see what that shows. Still, the
sunspots were clearly visible and I'm glad I have figured out how to
locate
the sun using the "scope-shadow" method.
Well done.
No, you won't see prominences. The problem is that there is just too much
light from the Sun itself, to see these relatively dark objects. The 'key'
to seeing these (when there isn't a Moon covering the Sun...), is to use
a special very narrow bandwidth filter, which
lets through only the H-alpha band. Unfortunately (the downside), these
filters are just about the most accurate optical surfaces made, and are
expensive (a 1.5" one, will cost about twice what your scope cost...). These
are used instead of the 'visible light' filter that you have, and are one of
the tools used by people wanting to observe detail on the Sun.
You may well be suprised at how much sunspots will change from day to day,
and the strange shapes these take. If you have a local astronomy club (or
even one further away), it is well worth finding out if there is anybody
there who might let you have a look through a scope equiped with an H-alpha
filter. It is well 'worth a look', especially if you can look soon
before/afterwards with the visible light filter, since the shapes,
formations, and patterns 'around' the visible spots, can be really
interesting.

Best Wishes

"Free Electron" wrote in message
...
I was trying to see
eruptions from the edge of the sun but never could

I have a few shots of what you can see in H alpha at.

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

and

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

If that is of any interest.

Kevin
www.kevsmith.com
www.siriusobservatoriesuk.com
DayStar Filters UK - The Ultimate solar experience - Unashamed plug!

In article , Orion wrote:
Unless you buy a Hydrogen-alpha filter, all you'll ever see is sunspots,
unless you get lucky enough to be on a path of totality for a total solar
eclipse...
Orion


You can see more than just sunspots (though, yeah, no prominences)
with a white-light filter:

* you can often see plages, bright areas near the sun's limb

* amazingly enough, you can see granulation, if the seeing isn't too bad,
and you get a nice sharp focus, and you can tune your eye
to pick out low-contrast detail. I've seen it a number of
times with my ST-90 refractor at ~30X plus a Baader filter,
and sometimes with other setups.

For some reason it's been harder to see with my and others'
8" SCTs with full- and part-aperture solar filters,
at higher magnification. I've seen it with that but only rarely.

* you can see limb darkening!
At daytime public astronomy events, in the trough of
the solar cycle, often the fading-off of brightness toward
the edge of the sun is the only feature that can be seen.
It's nice to talk about this -- its quantitative understanding
was important in astrophysical history. Though I admit, it's
not the kind of visual feature that will make you
want to dig out the solar filter every day.

This gives an excuse to re-tell somebody's astronomy geek joke.
I'd heard that at some Texas Star Party (I've never been there)
someone once wore a t-shirt that read:

Limb Darkening

Early Treatment
Saves Lives

Whoever made this one up, I'd like to shake his or her hand.
Anyone remember seeing this shirt, or know anything about it??

Stuart Levy

In article , Stephen Paul wrote:

"Stuart Levy" wrote in message
.. .
In article , Orion wrote:

Unless you buy a Hydrogen-alpha filter, all you'll ever see is sunspots,

* amazingly enough, you can see granulation, if the seeing isn't too
bad,
and you get a nice sharp focus, and you can tune your eye
to pick out low-contrast detail.

Low contrast......


For some reason it's been harder to see with my and others'
8" SCTs with full- and part-aperture solar filters,

..... 33% obstruction?

I'd been guessing more that it was hard to pick out those
low-contrast features at higher power (low spatial frequency)
than that diffraction was smearing them out. Things always seem
sharper at lower power.

Maybe I should try a high-power eyepiece in the ST-90
(giving the same magnification as a low-power eyepiece in the SCT,
say 60x or 90x) and see if the granulation goes away.
If it's still visible in the ST-90, I might believe you.
But generally I suspect that obstructions are overrated in how
they affect your view, as most optical systems aren't ideal otherwise.

(My 12-year-old Meade 8" suffers pretty badly from spherical
aberration, as I tested by measuring point-of-best-focus
with various aperture masks. That certainly affects it
much more than its central obstruction! Other people's Meade SCTs
don't seem as bad that way.)

Stuart