Missed the GRS

I have a homebuilt 6"/f8 I completed recently. There was a Red Spot
transit at ~11 pm last night, local time, so I went out around 10:30 to
check for it. I used a 32 mm eyepiece and a 7.5 and then each with a 2x
barlow (that's 38x, 75x, 160x and 320x magnification). I can't honestly
say I saw it. My best guess as to its location seems to be where it
actually was, but it was very, very faint and blurry.

As for the blurry, I've been thinking my scope is not collimated well.
I don't have a laser collimator and I don't want to spend $X to buy one
so I've been doing it by eye. But I'm a n00b, so I'm probably not doing
it well. Are there some objective measures of how close I'm coming that
are better than "my eyeball seems to be about in the middle"?

Also, how much of an effect will my laziness have: I'm not letting the
scope cool down. I just ran right out and started using it.

Do you know of anyone that shoots 35mm film? If you can get a kodak film
can(plastic) you can make a ultracheap linement tool for your scope, then
just dot the center of the main mirror and you'll get lot better viewing


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"Anonymous AtWork" wrote in message
...
I have a homebuilt 6"/f8 I completed recently. There was a Red Spot
transit at ~11 pm last night, local time, so I went out around 10:30 to
check for it. I used a 32 mm eyepiece and a 7.5 and then each with a 2x
barlow (that's 38x, 75x, 160x and 320x magnification). I can't honestly
say I saw it. My best guess as to its location seems to be where it
actually was, but it was very, very faint and blurry.

As for the blurry, I've been thinking my scope is not collimated well. I
don't have a laser collimator and I don't want to spend $X to buy one so
I've been doing it by eye. But I'm a n00b, so I'm probably not doing it
well. Are there some objective measures of how close I'm coming that are
better than "my eyeball seems to be about in the middle"?

Also, how much of an effect will my laziness have: I'm not letting the
scope cool down. I just ran right out and started using it.

Starlord wrote:
Do you know of anyone that shoots 35mm film? If you can get a kodak film
can(plastic) you can make a ultracheap linement tool for your scope, then
just dot the center of the main mirror and you'll get lot better viewing



As a matter of fact, I already dotted the center of the primary AND made
a film can alignment tool. I'm still not convinced it's good, though.
Is it really enough to just line the dot up with the center? It seems
like you could have the centers of everything lined up without the the
surrounding surfaces being right.

Collimation matters. BUT you can get close enough by defocussing---in and
out. If the bullseye is symmetrical, you're good. The GRS is not easy or
obvious. Try again Thursday night and you'll catch a transit too! If you
can see the transit, look for the shadow. If you can see that, look for the
GRS. It's much more pale than the pictures generally show it to be.

Doink
"Anonymous AtWork" wrote in message
...
I have a homebuilt 6"/f8 I completed recently. There was a Red Spot
transit at ~11 pm last night, local time, so I went out around 10:30 to
check for it. I used a 32 mm eyepiece and a 7.5 and then each with a 2x
barlow (that's 38x, 75x, 160x and 320x magnification). I can't honestly
say I saw it. My best guess as to its location seems to be where it
actually was, but it was very, very faint and blurry.

As for the blurry, I've been thinking my scope is not collimated well. I
don't have a laser collimator and I don't want to spend $X to buy one so
I've been doing it by eye. But I'm a n00b, so I'm probably not doing it
well. Are there some objective measures of how close I'm coming that are
better than "my eyeball seems to be about in the middle"?

Also, how much of an effect will my laziness have: I'm not letting the
scope cool down. I just ran right out and started using it.

Doink wrote:
Collimation matters. BUT you can get close enough by defocussing---in and
out. If the bullseye is symmetrical, you're good.

defocussing?

The GRS is not easy or
obvious. Try again Thursday night and you'll catch a transit too! If you
can see the transit, look for the shadow. If you can see that, look for the
GRS. It's much more pale than the pictures generally show it to be.

Good info, thanks. But I think I'll have to wait until Saturday for a
transit that occurs when it is reasonably dark. IO at around 2 am UT on
7/01.

http://skyandtelescope.com/observing...cle_830_2.asp#

Doink
"Anonymous AtWork" wrote in message
...
I have a homebuilt 6"/f8 I completed recently. There was a Red Spot
transit at ~11 pm last night, local time, so I went out around 10:30 to
check for it. I used a 32 mm eyepiece and a 7.5 and then each with a 2x
barlow (that's 38x, 75x, 160x and 320x magnification). I can't honestly
say I saw it. My best guess as to its location seems to be where it
actually was, but it was very, very faint and blurry.

As for the blurry, I've been thinking my scope is not collimated well. I
don't have a laser collimator and I don't want to spend $X to buy one so
I've been doing it by eye. But I'm a n00b, so I'm probably not doing it
well. Are there some objective measures of how close I'm coming that are
better than "my eyeball seems to be about in the middle"?

Also, how much of an effect will my laziness have: I'm not letting the
scope cool down. I just ran right out and started using it.

Do you know of anyone that shoots 35mm film? If you can get a kodak film
can(plastic) you can make a ultracheap linement tool for your scope, then
just dot the center of the main mirror and you'll get lot better viewing



As a matter of fact, I already dotted the center of the primary AND made a
film can alignment tool. I'm still not convinced it's good, though. Is it
really enough to just line the dot up with the center? It seems like you
could have the centers of everything lined up without the the surrounding
surfaces being right.

The quality of your views will depend on:
1) the quality of the optics - for a newt the primary and secondary mirrors.
2) allowing the optics to come to thermal equillibrium (cool-down).
3) the seeing, about which you can do very little except to avoid locally
bad seeing like observing directly over a hot roof, etc.

You should check your collimation (and optics) by doing a star test (use
Polaris). This will allow you to precisely align your primary, assuming
that everything else is right on, i.e. focuser square, secondary properly
positioned/rotated, secondary pointing at center of primary. A 6" f/8 can
be off quite a bit and give ok views, but for great views must be pretty
much right on. If you made the mirror I suspect that it might not be great,
but I certainly don't know that. The star test will tell you what is going
on. See, for starters:
http://aberrator.astronomy.net/html/...r-testing.html

As far as the GRS goes, it will not look red, or anything like it, but more
like a hole in the band. Join your local astro club, and compare your views
to what others are getting.

Dennis

Dennis Woos wrote:
As far as the GRS goes, it will not look red, or anything like it, but more
like a hole in the band. Join your local astro club, and compare your views
to what others are getting.

For those who can't get to a club, here's what it looks like to me, in
a small scope. Take a piece of white paper, and a brown colored pencil.
Draw a light band, then erase an oval shaped dent at the bottom edge of
the belt. The GRS looks like that remnant of color that remains after
you erase.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html

John Steinberg wrote:
Brian Tung wrote:

For those who can't get to a club, here's what it looks like to me, in
a small scope. Take a piece of white paper, and a brown colored pencil.

A PMS number might help here. (So many browns, so little time.)

Another way to achieve a simulated GRS, and save some effort, is to
look at some online GRS sketches.

http://www.rangeweb.net/~sketcher/
http://astro.geekjoy.com/sketchgalle..._sketches.html

And finally....
http://astro.geekjoy.com/sketchgalle..._sketches.html

Which may approximate Dr. Tung's suggestion best.

I've always found the GRS to be a visual snorefest but give me a
transit and I'm all over that like a fat kid on a cupcake.

Based on these descriptions, I probably did see it but wasn't impressed.
After all, I did correctly guess where it was on the face. I knew it
wasn't going to be bright red like in some photos but I didn't expect it
to look like eraser crumbs either.

I'll look for a moon transit.

On Wed, 28 Jun 2006 14:13:27 -0400, the GJS (great John Steinberg) wrote:

give me a
transit and I'm all over that like a fat kid on a cupcake.


I am all over it like a fly on poop.


--
Martin R. Howell

"The Astro Post"
www.theastropost.com

John Steinberg wrote:
A PMS number might help here. (So many browns, so little time.)

Another way to achieve a simulated GRS, and save some effort, is to
look at some online GRS sketches.

Actually, I meant it as a kind of thought experiment. Oops.

I've always found the GRS to be a visual snorefest but give me a
transit and I'm all over that like a fat kid on a cupcake.

I like 'em both.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html