Date   

AP900 CP4 with ASIAIR - need some guidance

Dan_Paris
 

   Hi everyone,

since yesterday I am a happy owner of an AP900 with CP4 upgrade. What a beautiful an impressive mount! 

Coming from a Skywatcher AZ-EQ6 driven by an ASIAIR using EQMOD, I tried to use the AP900 in the same way.

I connected the ASIAIR to the CP4 with an USB cable, an turned everything on. After choosing "Astro-physics CP3/CP4" in the mount menu of the ASIAIR, the mount was instantly recognized and reacted to the arrow buttons on the phone screen. So far so good.  I then tried to simulate a full imaging session.  Everything eventually worked but there was some oddities:

  1. When I ran the polar alignement procedure, after the first plate solve the mount moved in RA (as it should) but the displayed angle stayed at 0° and the motion stopped then midway. To remedy this I had to first point the mount away from the pole, take a picture, sync the mount, come back to park 3 position (all with ASIAIR), before launching PA.
  2. I sent a GOTO command with the ASIAIR to M13, which was then 1h30m east of the meridian. However the mount moved in the "wrong" direction and ended up counterweight up (fortunately the scope cleared the mount - but not by much). I sent after that another GOTO command to M51 (which was about 2h west of the meridian) and this time the mount was in the standard position, i.e. counterweights down.
  3. I tried to calibrate autoguiding. The West steps were as they should (small), but when it reverted to East, the mount made a very large motion (enough to put the guide star out of the FOV). I tried then to enforce guiding speed 1x with the GTO keypad first, it worked but only to some extent (the star was lost but eventually found).
I managed to take few autoguided frames and the results are very encouraging - significantly tighter stars than with my previous mount. 

I am wondering whether there are extra steps or settings that would make the dialog between the ASIAIR and the CP4 smoother ?

Thanks for your help,

Dan


Re: Field Rotation

Ray Gralak
 

I do this routinely every time I am out testing scopes and mounts. A star's position will change in the sky from
beginning to end. The RA/Dec will change, so that the reported coordinates after a plate solve will come out
different. I see this every night that I am imaging. And it has zero to do with any cable snags or other mechanical
issues. It is pure and simple atmospheric refraction that is bending the tracking path of an object.
Roland, I sent you a private email, but when auto-guiding, the guide star is usually not far from the area being imaged, so the guide star is *also* refracted. Thus the only refraction effect is the difference between the refraction seen at the guide scope and the main scope, which is usually pretty small.

-Ray


Re: Field Rotation

 

Mike are your stars not round? I was under the impression you just had some shift in your images


On Thu, Jun 2, 2022 at 7:37 PM M Hambrick <mhambrick563@...> wrote:
OK I guess I misunderstood what you said about modeling. I was thinking that it would help.

So, what is the secret to taking guided 5-to-10-minute images with perfectly round stars ? 

Mike




Re: Field Rotation

M Hambrick
 

OK I guess I misunderstood what you said about modeling. I was thinking that it would help.

So, what is the secret to taking guided 5-to-10-minute images with perfectly round stars ? 

Mike


Re: APCC fast what if

Eric Claeys
 
Edited

There is a super cheap version of Sky Safari, a more expensive one, then the Pro version.  More money gets you more objects plus some other things - see their website.

Eric


Re: APCC fast what if

Roland Christen
 

Great. Post some when you can.

Rolando

-----Original Message-----
From: Shailesh Trivedi <shailesh.trivedi@...>
To: main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 5:08 pm
Subject: Re: [ap-gto] APCC fast what if

Reporting back. I used Roland's method to determine when the Squid nebula would rise above the  2nd story of my house (using my planetarium software) and arrived at 12:35am. I am happy to report that this worked using SGP and now I have a method to image it while I sleep. I have captured images which are decidedly Ha and Oiii (not my house).

Thanks to everyone for provided methods which worked for you. 

Shailesh

--
Roland Christen
Astro-Physics


Re: APCC fast what if

Shailesh Trivedi
 

Reporting back. I used Roland's method to determine when the Squid nebula would rise above the  2nd story of my house (using my planetarium software) and arrived at 12:35am. I am happy to report that this worked using SGP and now I have a method to image it while I sleep. I have captured images which are decidedly Ha and Oiii (not my house).

Thanks to everyone for provided methods which worked for you. 

Shailesh


Re: Field Rotation

Roland Christen
 


  1. Try off-axis guiding rather than using a separate guide scope & camera.
  2. Try building a pointing model in APCC to see if there is a reduction in the drift.
  3. Move to Hawaii where the sky must be more linear. I'll bet there are still lots of vacant lots in Kohala Ranch :>)
None of what you posted above will do anything to change what happens. I tried to explain what is happening (atmospheric refraction bends the path), but if you guys really must chase this red herring, then I am at a loss as to how to explain a simple natural phenomenon.

Rolando

-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 3:02 pm
Subject: Re: [ap-gto] Field Rotation

Thanks everyone for the comments.

To Ray's comment, my guide scope and main scope are not perfectly aligned, but they are within a dozen or so arc-minutes of pointing to the same spot. I am not particularly picky about the guide star as long as it is within the center 1/2 of the guide scope field of view. For any given image, the guide star I choose is probably within a few dozen arc-minutes of the center of the main image.

The main scope is a 180 EDT with a 3.5-inch focuser and Quad TCC with a SBIG STXL16200. The guide scope is a Tele-Vue Pronto with a SBIG ST2000 camera. The main and guide scopes are in a side-by side arrangement on an 1100 GTO (non AE) mount. It is pretty well balanced in RA and Declination, and I always tie off my cables at the pier to minimize the length of hanging cables. 

I use a RAPAS for polar alignment, but since I have a portable setup I have never bothered to set up a model. I will have to try it though to see if I can see a difference per Roland's comments.

Per Brian's comment. I didn't stack my images but plate solved the first and last image of the night to calculate the shift in the center of the image which I mentioned above to be 7.91" in RA and 25.5" in Declination over the 5 hour period. If I look at the images throughout the evening you can see that this drift is continuous and pretty consistent. I do not see any sudden shifts that would indicate a shift in the imaging train.

I have two (maybe three) takeaways from this thread to see if I can improve this:

  1. Try off-axis guiding rather than using a separate guide scope & camera.
  2. Try building a pointing model in APCC to see if there is a reduction in the drift.
  3. Move to Hawaii where the sky must be more linear. I'll bet there are still lots of vacant lots in Kohala Ranch :>)

Mike

Mike

--
Roland Christen
Astro-Physics


Re: Field Rotation

Roland Christen
 

You are chasing a red herring down a blind alley.

Rolando

-----Original Message-----
From: Steve Reilly <sreilly24590@...>
To: main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 2:49 pm
Subject: Re: [ap-gto] Field Rotation

And dithered guiding would also contribute no?
 
Steve
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Brian Valente
Sent: Thursday, June 2, 2022 3:31 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Field Rotation
 
>>> Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.
 
What is unclear to me is if the images inbetween start and end show a slow change in position on the sensor, or if there are one or more sudden jumps (which would indicate mechanical issues: cable snag, flexure, etc.)
 
On Thu, Jun 2, 2022 at 12:19 PM Ray Gralak <iogroups@...> wrote:
Hi Roland,

> Even if you are autoguiding, the tiny corrections from the autoguider add up over time and will even show up on
> your planetarium program as a slow shift.

Yes, because in the act of guiding the mount's RA and Dec can change, which is what is reflected in the planetarium program. But this does not mean that the actual sky RA/Dec of the guide star has changed

Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

-Ray






 
--

--
Roland Christen
Astro-Physics


Re: Field Rotation

Roland Christen
 


What is unclear to me is if the images inbetween start and end show a slow change in position on the sensor, or if there are one or more sudden jumps (which would indicate mechanical issues: cable snag, flexure, etc.)
I do this routinely every time I am out testing scopes and mounts. A star's position will change in the sky from beginning to end. The RA/Dec will change, so that the reported coordinates after a plate solve will come out different. I see this every night that I am imaging. And it has zero to do with any cable snags or other mechanical issues. It is pure and simple atmospheric refraction that is bending the tracking path of an object.

If you want, I am out tonight testing and imaging, and I will show you on the planetarium program how far the guide star moves during an imaging run, even though it is bang on the crosshairs during all this time.

Roland

-----Original Message-----
From: Brian Valente <bvalente@...>
To: main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 2:30 pm
Subject: Re: [ap-gto] Field Rotation

>>> Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

What is unclear to me is if the images inbetween start and end show a slow change in position on the sensor, or if there are one or more sudden jumps (which would indicate mechanical issues: cable snag, flexure, etc.)

On Thu, Jun 2, 2022 at 12:19 PM Ray Gralak <iogroups@...> wrote:
Hi Roland,

> Even if you are autoguiding, the tiny corrections from the autoguider add up over time and will even show up on
> your planetarium program as a slow shift.

Yes, because in the act of guiding the mount's RA and Dec can change, which is what is reflected in the planetarium program. But this does not mean that the actual sky RA/Dec of the guide star has changed

Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

-Ray








--

--
Roland Christen
Astro-Physics


Re: Field Rotation

Roland Christen
 


But this does not mean that the actual sky RA/Dec of the guide star has changed
Yes, the star's theoretical RA/Dec is constant. However, if you plate solve that star when it's overhead and call that the theoretical RA/Dec, then when you plate solve it at another point in the sky the RA/Dec of where that star ends up will be different.

Roland

-----Original Message-----
From: Ray Gralak <iogroups@...>
To: main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 2:19 pm
Subject: Re: [ap-gto] Field Rotation

Hi Roland,

> Even if you are autoguiding, the tiny corrections from the autoguider add up over time and will even show up on
> your planetarium program as a slow shift.

Yes, because in the act of guiding the mount's RA and Dec can change, which is what is reflected in the planetarium program. But this does not mean that the actual sky RA/Dec of the guide star has changed

Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

-Ray







--
Roland Christen
Astro-Physics


Re: Field Rotation

M Hambrick
 

Thanks everyone for the comments.

To Ray's comment, my guide scope and main scope are not perfectly aligned, but they are within a dozen or so arc-minutes of pointing to the same spot. I am not particularly picky about the guide star as long as it is within the center 1/2 of the guide scope field of view. For any given image, the guide star I choose is probably within a few dozen arc-minutes of the center of the main image.

The main scope is a 180 EDT with a 3.5-inch focuser and Quad TCC with a SBIG STXL16200. The guide scope is a Tele-Vue Pronto with a SBIG ST2000 camera. The main and guide scopes are in a side-by side arrangement on an 1100 GTO (non AE) mount. It is pretty well balanced in RA and Declination, and I always tie off my cables at the pier to minimize the length of hanging cables. 

I use a RAPAS for polar alignment, but since I have a portable setup I have never bothered to set up a model. I will have to try it though to see if I can see a difference per Roland's comments.

Per Brian's comment. I didn't stack my images but plate solved the first and last image of the night to calculate the shift in the center of the image which I mentioned above to be 7.91" in RA and 25.5" in Declination over the 5 hour period. If I look at the images throughout the evening you can see that this drift is continuous and pretty consistent. I do not see any sudden shifts that would indicate a shift in the imaging train.

I have two (maybe three) takeaways from this thread to see if I can improve this:

  1. Try off-axis guiding rather than using a separate guide scope & camera.
  2. Try building a pointing model in APCC to see if there is a reduction in the drift.
  3. Move to Hawaii where the sky must be more linear. I'll bet there are still lots of vacant lots in Kohala Ranch :>)

Mike

Mike


Re: Field Rotation

 

that's another possibility, especially if it's spiral dither in both axis


On Thu, Jun 2, 2022 at 12:49 PM Steve Reilly <sreilly24590@...> wrote:

And dithered guiding would also contribute no?

 

Steve

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Brian Valente
Sent: Thursday, June 2, 2022 3:31 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Field Rotation

 

>>> Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

 

What is unclear to me is if the images inbetween start and end show a slow change in position on the sensor, or if there are one or more sudden jumps (which would indicate mechanical issues: cable snag, flexure, etc.)

 

On Thu, Jun 2, 2022 at 12:19 PM Ray Gralak <iogroups@...> wrote:

Hi Roland,

> Even if you are autoguiding, the tiny corrections from the autoguider add up over time and will even show up on
> your planetarium program as a slow shift.

Yes, because in the act of guiding the mount's RA and Dec can change, which is what is reflected in the planetarium program. But this does not mean that the actual sky RA/Dec of the guide star has changed

Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

-Ray






 

--




Re: Field Rotation

Steve Reilly
 

And dithered guiding would also contribute no?

 

Steve

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Brian Valente
Sent: Thursday, June 2, 2022 3:31 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Field Rotation

 

>>> Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

 

What is unclear to me is if the images inbetween start and end show a slow change in position on the sensor, or if there are one or more sudden jumps (which would indicate mechanical issues: cable snag, flexure, etc.)

 

On Thu, Jun 2, 2022 at 12:19 PM Ray Gralak <iogroups@...> wrote:

Hi Roland,

> Even if you are autoguiding, the tiny corrections from the autoguider add up over time and will even show up on
> your planetarium program as a slow shift.

Yes, because in the act of guiding the mount's RA and Dec can change, which is what is reflected in the planetarium program. But this does not mean that the actual sky RA/Dec of the guide star has changed

Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

-Ray






 

--


Re: Field Rotation

 

>>> Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

What is unclear to me is if the images inbetween start and end show a slow change in position on the sensor, or if there are one or more sudden jumps (which would indicate mechanical issues: cable snag, flexure, etc.)

On Thu, Jun 2, 2022 at 12:19 PM Ray Gralak <iogroups@...> wrote:
Hi Roland,

> Even if you are autoguiding, the tiny corrections from the autoguider add up over time and will even show up on
> your planetarium program as a slow shift.

Yes, because in the act of guiding the mount's RA and Dec can change, which is what is reflected in the planetarium program. But this does not mean that the actual sky RA/Dec of the guide star has changed

Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

-Ray









Re: Field Rotation

Ray Gralak
 

Hi Roland,

Even if you are autoguiding, the tiny corrections from the autoguider add up over time and will even show up on
your planetarium program as a slow shift.
Yes, because in the act of guiding the mount's RA and Dec can change, which is what is reflected in the planetarium program. But this does not mean that the actual sky RA/Dec of the guide star has changed

Mike said he plate-solved the starting and ending images and the coordinates were off by a few tens of arc-seconds. This is an actual shift in stars and sky position independent of any change in RA/Dec mount coordinates.

-Ray


Re: Field Rotation

Roland Christen
 

Polar align you mount as best you can. It keeps your drift to a minimum and makes it easier on your guiding software.

Roland

-----Original Message-----
From: Steve Reilly <sreilly24590@...>
To: main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 12:14 pm
Subject: Re: [ap-gto] Field Rotation

I might should have maybe mentioned I image with a 12.5” RC and AP1200GTO with a image scale of 0.62 arc seconds.
 
-Steve
 


--
Roland Christen
Astro-Physics


Re: Field Rotation

Roland Christen
 


I had always thought that having it too close was harder for guiding as it would be rocking on both sides to correct.
That may apply to cheap mounts that have no spring loaded worms. Does not apply here.

Roland

-----Original Message-----
From: Steve Reilly <sreilly24590@...>
To: main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 12:13 pm
Subject: Re: [ap-gto] Field Rotation

Just for clarity what is considered suitable imaging alignment? How close do you want the PA to be? I had always thought that having it too close was harder for guiding as it would be rocking on both sides to correct. Maybe that’s outdated thinking…From what I see and Ray informed me of I’m think my PA is OK but….
A screenshot of a computerDescription automatically generated with medium confidenceGraphical user interfaceDescription automatically generated with low confidence
 
Should I refine this? It’s Greek to me….
 
-Steve
 
 
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Roland Christen via groups.io
Sent: Thursday, June 2, 2022 12:17 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Field Rotation
 
Leveling the mount has no effect whatsoever on field rotation. A mount does not need to be level, the polar axis just needs to be pointed at the pole. That axis doesn't care where its support structure is pointing - it could be completely upside down or sideways, and it would make zero difference in the mount's tracking or pointing ability.
 
Rolando
 
-----Original Message-----
From: Howard Ritter via groups.io <
howard.ritter@...>
To:
main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 10:59 am
Subject: Re: [ap-gto] Field Rotation
That seems counterintuitive. The mount should be insensitive to leveling error, since the process of polar alignment with each new setting up accounts for any direction of out-of-level. And in any case, the process of leveling would seem to me to be pretty coarse by comparison, and the error in leveling far greater, than the error in aligning. Or am I misunderstanding something?
 
—howard


On Jun 2, 2022, at 10:39 AM, Andrew Burwell via groups.io <andrew_burwell@...> wrote:
 
I get slight field rotation if I'm not fully leveled. Especially if I rely on a bubble level. It's better to take the mount head off and properly level the tripod with something more reliable. I've also noticed on light weight tripods and mounts that the weight of the load can shift things slightly (flexure) on each side of the meridian causing a slight bit of rotation in the images once stacked. But in both cases it can easily be cropped from a final image without losing much data. But when properly leveled I still see a very tiny amount and still need to crop just a tad.
-Andrew
 

--
Roland Christen
Astro-Physics

--
Roland Christen
Astro-Physics


Re: Field Rotation

Steve Reilly
 

I might should have maybe mentioned I image with a 12.5” RC and AP1200GTO with a image scale of 0.62 arc seconds.

 

-Steve

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Steve Reilly via groups.io
Sent: Thursday, June 2, 2022 1:13 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Field Rotation

 

Just for clarity what is considered suitable imaging alignment? How close do you want the PA to be? I had always thought that having it too close was harder for guiding as it would be rocking on both sides to correct. Maybe that’s outdated thinking…From what I see and Ray informed me of I’m think my PA is OK but….

A screenshot of a computer

Description automatically generated with medium confidenceGraphical user interface

Description automatically generated with low confidence

 

Should I refine this? It’s Greek to me….

 

-Steve

 

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Roland Christen via groups.io
Sent: Thursday, June 2, 2022 12:17 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Field Rotation

 

Leveling the mount has no effect whatsoever on field rotation. A mount does not need to be level, the polar axis just needs to be pointed at the pole. That axis doesn't care where its support structure is pointing - it could be completely upside down or sideways, and it would make zero difference in the mount's tracking or pointing ability.

 

Rolando

 

-----Original Message-----
From: Howard Ritter via groups.io <
howard.ritter@...>
To:
main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 10:59 am
Subject: Re: [ap-gto] Field Rotation

That seems counterintuitive. The mount should be insensitive to leveling error, since the process of polar alignment with each new setting up accounts for any direction of out-of-level. And in any case, the process of leveling would seem to me to be pretty coarse by comparison, and the error in leveling far greater, than the error in aligning. Or am I misunderstanding something?

 

—howard

 

On Jun 2, 2022, at 10:39 AM, Andrew Burwell via groups.io <andrew_burwell@...> wrote:

 

I get slight field rotation if I'm not fully leveled. Especially if I rely on a bubble level. It's better to take the mount head off and properly level the tripod with something more reliable. I've also noticed on light weight tripods and mounts that the weight of the load can shift things slightly (flexure) on each side of the meridian causing a slight bit of rotation in the images once stacked. But in both cases it can easily be cropped from a final image without losing much data. But when properly leveled I still see a very tiny amount and still need to crop just a tad.
-Andrew

 


--
Roland Christen
Astro-Physics


Re: Field Rotation

Steve Reilly
 

Just for clarity what is considered suitable imaging alignment? How close do you want the PA to be? I had always thought that having it too close was harder for guiding as it would be rocking on both sides to correct. Maybe that’s outdated thinking…From what I see and Ray informed me of I’m think my PA is OK but….

A screenshot of a computer

Description automatically generated with medium confidenceGraphical user interface

Description automatically generated with low confidence

 

Should I refine this? It’s Greek to me….

 

-Steve

 

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Roland Christen via groups.io
Sent: Thursday, June 2, 2022 12:17 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Field Rotation

 

Leveling the mount has no effect whatsoever on field rotation. A mount does not need to be level, the polar axis just needs to be pointed at the pole. That axis doesn't care where its support structure is pointing - it could be completely upside down or sideways, and it would make zero difference in the mount's tracking or pointing ability.

 

Rolando

 

-----Original Message-----
From: Howard Ritter via groups.io <
howard.ritter@...>
To:
main@ap-gto.groups.io
Sent: Thu, Jun 2, 2022 10:59 am
Subject: Re: [ap-gto] Field Rotation

That seems counterintuitive. The mount should be insensitive to leveling error, since the process of polar alignment with each new setting up accounts for any direction of out-of-level. And in any case, the process of leveling would seem to me to be pretty coarse by comparison, and the error in leveling far greater, than the error in aligning. Or am I misunderstanding something?

 

—howard



On Jun 2, 2022, at 10:39 AM, Andrew Burwell via groups.io <andrew_burwell@...> wrote:

 

I get slight field rotation if I'm not fully leveled. Especially if I rely on a bubble level. It's better to take the mount head off and properly level the tripod with something more reliable. I've also noticed on light weight tripods and mounts that the weight of the load can shift things slightly (flexure) on each side of the meridian causing a slight bit of rotation in the images once stacked. But in both cases it can easily be cropped from a final image without losing much data. But when properly leveled I still see a very tiny amount and still need to crop just a tad.
-Andrew

 


--
Roland Christen
Astro-Physics

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