A question of viewing

So I was looking through my new (used) 10 inch dobs last night.
Saturn looked great I could even see a band. (or maybe it was the Cassini
space craft--- Grin)
I also look at Sirius and it looked -- well --umm--- grainy.
Was this the viewing last night in Long Beach, Ca.
Or do I have work to do on the scope?
Thanks Mark
--
Fly Lexx!

On Wed, 23 Apr 2008 23:51:37 GMT, "Mark F." wrote:

So I was looking through my new (used) 10 inch dobs last night.
Saturn looked great I could even see a band. (or maybe it was the Cassini
space craft--- Grin)
I also look at Sirius and it looked -- well --umm--- grainy.
Was this the viewing last night in Long Beach, Ca.
Or do I have work to do on the scope?

It will be rare for Sirius to look like a steady point. First of all,
being a point source, its light reaches you through an extremely narrow
column of air, so all sorts of seeing effects cause disruptions. This is
different from planets, which subtend a finite angle. The effect is
moderated somewhat by the large aperture of the telescope (which is why
you don't usually see stars twinkle telescopically), but it's still
there. Second, a bright point source highlights every optical aberration
in your system. Are you saying Sirius looked different last night than
it usually does?
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Mark F. wrote:

I also look at Sirius and it looked -- well --umm--- grainy.
Was this the viewing last night in Long Beach, Ca.
Or do I have work to do on the scope?

Sounds like an effect of air turbulence: see for example
Texereau, "How to Make a Telescope" (Willmann-Bell 1984)
Fig. 15.2 (p. 292) for a drawing showing the effect of
various degrees of turbulence on a point source image:
if it is sufficiently severe, the central "disk" of the
diffraction pattern looks more like a speckled, granular
blob...

-dave w

On Wed, 23 Apr 2008 23:51:37 GMT, Mark F. wrote:

So I was looking through my new (used) 10 inch dobs last night.
Saturn looked great I could even see a band. (or maybe it was the Cassini
space craft--- Grin)
I also look at Sirius and it looked -- well --umm--- grainy.
Was this the viewing last night in Long Beach, Ca.
Or do I have work to do on the scope?
Thanks Mark

It could be that your bigger scope has introduced you to tube currents and
a larger mirror's inability to reach thermal equilibrium in a timely
fashion than you were used to with your smaller scope. The infinitely
larger image of Saturn through the scope could seem less corrupted to your
eyes than the point of light to which Sirius translates.


--
Martin R. Howell
Moderated sci.astro.amateur
www.moderatedsciastroamateur.org
** Posted from http://www.teranews.com **

Different in that I am using a 10 inch dobs for the first time, I was using
a 4.5 dobs.
So I was looking through both scopes last night and trying to compare what I
see.
And then ask the good people here for a little of there knowledge.
I am abput to try it again tonight and see what I come up with.


Thanks Mark



"Chris L Peterson" wrote in message
...
On Wed, 23 Apr 2008 23:51:37 GMT, "Mark F." wrote:

So I was looking through my new (used) 10 inch dobs last night.
Saturn looked great I could even see a band. (or maybe it was the Cassini
space craft--- Grin)
I also look at Sirius and it looked -- well --umm--- grainy.
Was this the viewing last night in Long Beach, Ca.
Or do I have work to do on the scope?

It will be rare for Sirius to look like a steady point. First of all,
being a point source, its light reaches you through an extremely narrow
column of air, so all sorts of seeing effects cause disruptions. This is
different from planets, which subtend a finite angle. The effect is
moderated somewhat by the large aperture of the telescope (which is why
you don't usually see stars twinkle telescopically), but it's still
there. Second, a bright point source highlights every optical aberration
in your system. Are you saying Sirius looked different last night than
it usually does?
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

47 year old eyes.
I do have floater though.

Mark



"Sam Wormley" wrote in message
news:s9SPj.79868$TT4.44664@attbi_s22...
Mark F. wrote:
So I was looking through my new (used) 10 inch dobs last night.
Saturn looked great I could even see a band. (or maybe it was the
Cassini space craft--- Grin)
I also look at Sirius and it looked -- well --umm--- grainy.
Was this the viewing last night in Long Beach, Ca.
Or do I have work to do on the scope?
Thanks Mark

How old are your eyes? High magnification on bright sources
can show you defects in your own eyes.

How old are your eyes?


LOL..what an idiotic question. Probably the same age as the poster??? Duh?
Unless they are a cyborg that got refitted...

MTA wrote:
How old are your eyes?


LOL..what an idiotic question. Probably the same age as the poster??? Duh?
Unless they are a cyborg that got refitted...

Of course it is a perfectly valid question as it is well known that eye
problems are more likely as age increases and many eye problems only
present themselves under observing conditions.

How old is your brain?

(I'll add a :-) for the over sensitive or humor impaired)

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

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To reply take out your eye