I tried an experiment last night (10" LX-200, SuperWedge, 9 mm Meade reticle.) The polar setup scenario is to use wedge to center Polaris then center a Meade-selected overhead star using the control box. I have the current version of the software. The Meade directions further indicate that you can do it over and over again. After the first iteration, you hit "go to" when it asks you to set the scope's Decl and RA to initial conditions instead of setting to initial conditions. That way you can let the scope slew back and forth between Polaris and the Meade-selected star multiple times using the wedge to do the centering on Polaris and the control box to do the centering on the Meade selected star. It would seem that if you are careful, the scope eventually should slew between the two stars and display them centered exactly. Unfortunately I was unable to obtain convergence. I was able to get it close (within outer reticle circle) but convergence was random. I'm wondering if the scope slewing causes tiny changes to the wedge settings. We're talking *tiny* of course but pointing accuracy depends on *how* tiny.
[NOTE: When I began, convergence was very poor. I checked the scope's clock against WWV and found a 1 minute, 50 second error. Updated clock and seemed to get much better results. Have not thought this through yet so not sure if clock accuracy is really a player in the polar alignment scheme. Seems that it should be.]
After that, slew to NGC224 showed it partially outside the view field with the 26mm eyepiece. So it was off by several minutes.
Overall I'm happy with my new scope. Just trying to test its limits like the rest of you. Checked out a few double stars late last night to guage resolution and was disappointed until I realized that "dew"saster had struck my corrector plate! Unusual for dew here in Arizona desert although this *is* December so I perhaps should not have been surprised.
Howard
> have the current version of the software. The Meade directions
further
> indicate that you can do it over and over again. After the first
> iteration, you hit "go to" when it asks you to set the scope's
Decl and
> RA to initial conditions instead of setting to initial conditions.
> That way you can let the scope slew back and forth between Polaris
and
> the Meade-selected star multiple times using the wedge to do the
> centering on Polaris and the control box to do the centering on
the
> Meade selected star. It would seem that if you are careful, the
scope
> eventually should slew between the two stars and display them
centered
> exactly. Unfortunately I was unable to obtain convergence. I was
able
> to get it close (within outer reticle circle) but convergence
was
> random.
It's my impression based on Jason Ware-Dallas' discussion earlier in
this mail list that you won't easily get true "convergence"...check the
archives of the group or let Jason repeat his earlier method. I think the
way to go is to do only two really careful iterations. If the alignment
isn't satisfactory, don't do another iteration, but start from go again.
the manual is not particularly clear about that. >
> [NOTE: When I began, convergence was very poor. I checked the
scope's
> clock against WWV and found a 1 minute, 50 second error. Updated
clock
> and seemed to get much better results. Have not thought this through
> yet so not sure if clock accuracy is really a player in the polar
> alignment scheme. Seems that it should be.]
>
My guess is that you started from go after the clock adjustment, and
simply did a better job with all of your iterations than you did the first
time.
> After that, slew to NGC224 showed it partially outside the view
field
> with the 26mm eyepiece. So it was off by several minutes.
>
NGC224 is 180 minutes long. For it to be "off by several minutes" is
not bad at all, is it? Even HPP only promises "better than one minute"
accuracy. Careful non-HPP alt-az alignment only promises 2 arcmin accuracy.
If you're off by "several minutes", that's pretty darned good for a beginner,
I suspect. NGC244 will ALWAYS be partially outside the field of view: it's
too big to fit. (well, I guess the central, brighter region fits well enough,
though).
> Overall I'm happy with my new scope. Just trying to test its limits
> like the rest of you. Checked out a few double stars late last
night
> to guage resolution and was disappointed until I realized that
> "dew"saster had struck my corrector plate! Unusual for dew here
in
> Arizona desert although this *is* December so I perhaps should
not
> have been surprised.
>
> Howard
>
I had the same dewsaster, Howard: these thangs ain't newtonians! I
got myself an Orion dew-zapper heater and it works like a charm except
for the idiotic garter belt-like fastener: I threw that away and used multiple
turns of black rubber electrical tape to permanently fasten the heating
strip to the scope. They're ridiculously expensive for what they are, but
they're an overnight express away, time-wise.
Rob Preston rapr@med.pitt.edu
Two comments:
First, a while ago Ron Ezra of Meade indicated that when you sync, any time bias disappears. Mathematically, a time bias is indistinguishable from an hour angle bias in encode readout and in an error in the scopes longitude. So after the first sync time accuracy is not important (assuming your clock is not keeping grossly wrong time).
Second, I have converged using the Meade approach iteratively. It took about 10 iterations. I have moved the scope to a spot without a view of Polaris. Using a modified Meade approach, a 12mm eyepiece with crosshairs, and 10 iterations, I can get pointing accuracy of about 2 arc minutes for the stars in the iteration and only a little worse for other stars I can see. (This is the real point of the alignment reports, to see how others are doing and to know if you or your equipment are 'off')..
Ralph
Have been pondering the Meade alignment star errors and believe I have figured out a work-around that might allow more accurate Polar alignment.
I posted a message some time ago indicating that I had attempted to achieve convergence by repeating the Meade Polar alignment procedure several times. That was before the alignment star error data was posted. I now believe one source of the non-convergence was due to the slightly innacurate coordinates for Polaris within the Meade object library chips.
Several iterations of error data have been posted. That data appears to be somewhat inconsistent. It would be nice to achieve consensus regarding the *correct* R.A. and Dec. of the 33 alignment stars selected by Meade. The only thing I have at the moment is "Expert Astronomer" which agrees well with with the Regulus data point posted by Phil Hill. That hardly constitutes a statistical verification of either! So how about posting a set of Absolutely Guaranteed R.A. and Dec. values for the 33 Meade alignment stars. Preferably for two different dates so that people can test their various software packages for accuracy of the precession and nutation algorithms. Post data source, software used, etc. so that the results can be replicated and verified by others.
Data posted so far on Polaris does not seem to have converged to convincing values. Since Polaris is the primary basis for polar alignment, we need in particular to establish its value with certainty. We also need to know the values for the other alignment stars with certainty because they are also used in the alignment process.
Anyway, once we have values that we can absolutely believe in, below is a proposed work-around for the Polaris part of the polar alignment procedure using the wedge and version 3.30L of the Meade software. Check it out for bad assumptions and let me know what you think. I'm going to try it if the weather ever clears. (Can't believe I'm in the Arizona desert - its been like a rain forest lately. It was almost *foggy* yesterday!)
Proposed Polar Alignment Work-around for Polaris (relative to version 3.30L Meade software):
1. Carry out the procedure for polar alignment given on page 31 of the Meade Instruction Manual. It involves centering Polaris using the wedge then centering a star chosen by the Meade software using the Keypad Hand Controller. Remember the name of the star chosen by the Meade software. Let's call it star "X". We will use it again in step 6 below.
2. Get into mode 2 (Page 38).
3. Begin the procedure in paragraph "b. GO TO Menu Option".
4. Enter the LX-200 group's highly ACCURATE consensus values (Yet To Be Determined) for R.A. and Dec. of Polaris.
5. The Telescope will slew to the ACCURATE coordinates of Polaris. Center Polaris using only the wedge controls.
6. If star X happens to be an alignment star with little or no error within the Meade database, press STAR, select star X, GOTO star X, center star X using the keypad, then press and hold ENTER until "COORDINATES MATCHED" is signaled.
7. Repeat starting from step 2 until convergence is achieved.
If star X was an alignment star with significant error within the Meade database, then performing step 6 will introduce error. I do not see an easy way to compensate for star X errors.
The above assumes that the Meade internal Polar alignment software initially assumes a R.A. = 90.0 and Dec. = 0.0 position then slews to the position where it thinks Polaris is (a position that is in error by 4.61' according to Jason's data). The user then adjusts the wedge to center Polaris. The Meade software then chooses star "X", slews to it, asks the user to center it using the keypad. Then the user presses ENTER and the software does a CM#, Match Coordinates operation? If that is what it is doing then the work-around I have proposed should allow accurate alignment (discounting structural limitations already discussed by others of course.)
I will suggest that one of the dates should be J2000.0 that way NO ones software should have a problem. If you wish two dates for comparison of software, I would suggest then a total of three dates.
I am all for the set of 33 TRUE locations for say Jan 1, 1995 and Jan 1, 1996. I would suggest precession and nutation be included in the calcuations (however, if one or the other is omitted, then a simple indication of that is needed. This affects the error in the TRUE location provided). I chose to omit nutation in my calculations because the error, I believe, is on the order of 18 arc seconds.
Another question to ponder is how accurate do the star locations need to be? (perfect is an unrealistic goal :-))))
Ralph
From anderson Wed Jan 4 13:45:32 1995
To: lx200-l@netcom.com
Subject: Re: Polar Alignment Polaris-error Workaround -Reply 2
Content-Length: 1881
Status: RO X-Lines: 41
>
> Phil has done a nice job collecting information from FK5 to compare
to the
> Meade Database of stars for the 33 primary stars.
>
Agree.
> ... the numbers printed [in the manual] are not
> necessarily the numbers in the computer on the LX200!!
Also pertinent.
I was able to attempt my workaround for Polaris a couple of days ago and I believe I convinced myself that pointing accuracy was improved. The remaining source of error, the error in DIPHDA's coordinates, was, in my opinion, significant. The alignment procedure chose DIPHDA as the secondary star. Subsequently I chose STAR, NAME, DIPHDA, GOTO and then centered on DIPHDA as contained in the Meade database. I then used the MODE 2 GOTO coordinates procedure entering what I believe are more correct coordinates for DIPHDA and watched as the scope slewed to the new coordinates. The star moved about one quarter of the diameter of the view field in my scope (10", 9 mm eyepiece). As mentioned before, I know of no way to easily correct for errors in the coordinates of the secondary stars. I did achieve much better pointing accuracy, in my opinion, by using my work-around for Polaris. The remaining sources of error, the coordinates of the secondary stars, limits what is achievable. I would be willing to pay for an update to the rom chips to correct the database errors. [I would be willing to make my own rom chips! - Anyone know the format?]
I realize the "drift" method is still an alternative but I guess I believe that we are not giving the electronics and hardware a chance until the coordinates are corrected. DIPHDA was not listed as having significant error but if the scope has a published pointing accuracy that is less than the errors in the coordinates of the alignment stars then it seems obvious that the coordinates should be corrected before doing anything else.
Thanks
Howard
From anderson Thu Feb 23 14:12:53 1995
To: astrorcf@netcom.com
Subject: Re: LX200 Star Catalog Errors -Reply
Content-Length: 1533
Status: RO X-Lines: 34
> Howard;
>
> Would you mind sending me an E-mail with your method of getting around
> the guide star errors. i'd like to make it a post on the Web pages
and
> the ftp site. >
> Thanks in advance for everyone that it will help. >
> -RObert
Sorry for delay in reply have had lots of meetings recently and its during a break from one at the moment. I will send you the method within the next few days. I want to make some refinements to the instructions (such as doing certain operations twice in succession to allow the gears to *actually* settle on the right location, etc.) Have not had enough time lately. Have been getting pretty good results though so I believe the information would be useful for others.
Really would like to get errors corrected within Meade database. I don't mind paying for the chips and the effort it would take. Only 33 stars *really* matter. Other things can be located by other means if necessary. Meade (Scott Byrum) said in a letter to me evoked by comments I made on registration card: "The object library that we are incorporating into the LX200 was obtained and used with the permission of Sky Publishing. Any errors that may be present originate with the compilers of the data. At this time there are no plans to change data base." I suppose that means "Sky Publishing" is responsible for any errors?? Since "Sky Publishing" is "Sky and Telescope" I wonder how they feel about all this? Wonder if I should write to them and request a corrected chip set! :)
Thanks
Howard.
From anderson Fri Feb 24 10:36:09 1995
To: astrorcf@netcom.com
Subject: Re: LX200 Star Catalog Errors -Reply
Content-Length: 4197
Status: RO X-Lines: 100
> > > Howard;
> > >
> > > Would you mind sending me an E-mail with your method of getting
around
> > > the guide star errors. i'd like to make it a post on the Web
pages and
> > > the ftp site.
> > >
> > > Thanks in advance for everyone that it will help.
> > >
OK, believe I am happy with the data below.
Thanks
Howard
Have been pondering the Meade alignment star errors and believe I have figured out a work-around that allows more accurate Polar alignment.
I posted a message some time ago indicating that I had attempted to achieve convergence by repeating the Meade Polar alignment procedure several times. That was before the alignment star error data was posted. I now believe one source of the non-convergence was due to the innacurate coordinates for Polaris within the Meade object library chips.
Since Polaris is the primary basis for polar alignment, we need in particular to establish its value with certainty. We also need to know the values for the other alignment stars with certainty because they are also used in the alignment process.
Anyway, once you have CORRECT right ascension and declination values for Polaris (Jason Ware posted Polaris coordinates of 2 28 14 and +89 14 44 for 16 Dec 94 as an example), below is a work-around for the polar alignment procedure using the wedge and version 3.30L of the Meade software.
1. Carry out the procedure for polar alignment given on page 31 of the Meade Instruction Manual. It involves centering Polaris using the wedge then centering a star chosen by the Meade software using the Keypad Hand Controller. Remember the name of the star chosen by the Meade software. Let's call it star "X". We will use it again in step 8 below.
2. Get into mode 2 (Page 38 of Meade manual for LX200).
3. Begin the procedure in paragraph "b." "GO TO Menu Option".
4. Enter the CORRECT R.A. and Dec. of Polaris for today's date.
5. The Telescope will slew to the CORRECT coordinates of Polaris.
6. Repeat steps 2, 3, 4, and 5. This is necessary because, for some reason, it doesn't get it exactly right the first time. You can check the value displayed in the hand controller to see if the coordinates match the ones you entered. (You could make small pointing adjustments with the hand controller if necessary. At this point we want the electronics and gears to think they are pointing exactly at the *correct* RA and DEC for Polaris.)
7. Center Polaris using only the wedge controls.
8. If star X happens to be an alignment star with little or no error within the Meade database, press STAR, select star X, GOTO star X, GOTO star X again since the electronics, gears or whatever did not get it exactly right the first time (at least that is what happens with my scope).
9. Center star X using the keypad, then press and hold ENTER until "COORDINATES MATCHED" is signaled.
10. Press GOTO to see if the star stays centered. Sometimes it does not. You may wish to repeat step 9.
11. Repeat starting from step 2 until convergence is achieved. By "convergence" here I mean that after step 6, Polaris is centered in your reticle and after step 8, star X is centered in the view field.
If star X was an alignment star with significant error within the Meade database, then performing step 6 will introduce error. I do not see an easy way to compensate for star X errors.
By using the above procedure, I have been able to slew back and forth between Polaris and star "X" so that both stars are within 10 arc seconds of the center of the reticle. In particular, I have done that using Aldebaran.
Now, the problem is that Jason Ware posted data indicating that the Meade Aldebaran coordinates are in error by 172.7 arc seconds. That means that we still have 172.7 plus or minus 10 arc seconds of error in the system. I do not see how to eliminate that error unless the Meade database for Aldebaran is corrected. It is my belief that the electronics and mechanics of the system are not the limiting factors for its pointing accuracy at the moment. The database errors in the 33 alignment stars are the limiting factor, i.e., the scope is much better than the database is allowing it to be.
From anderson Wed Mar 8 11:39:29 1995
To: astrorcf@netcom.com
Subject: Re: LX200 Star Catalog Errors -Reply
Content-Length: 6699
Status: RO X-Lines: 137
> I want to be VERY careful that this can't be used by someone to flame
> Meade for having problems with the LX200. Is there anyway you could
edit
> to remove remarks about errors in the Meade Object LIbrary ?? I know
> this is difficult since it's true that there are errors. Perhaps
> something to the effect of errors in the database that Meade licenses
> for use in the LX200. Its a tough one, but I'm *ultra* sensitive
to the
> fact that people just love to slam Meade. I don't wan't to provide
> ammunition in a post desgined to be helpful.
Ok, Iteration 3 is below. It is hard to explain why one would want to use a work-around if there are no errors that made it necessary. :) I don't want Meade to be subjected to any static either. I would like to be able to buy a corrected database though and wish there were a way to convince them to make the corrections and provide the upgrade chips. To give you more of the flavor of what we are faced with in that regard, here is more of the letter I received from Scott Byrum of Meade:
"The object library that we are incorporating into the LX200 was obtained and used with the permission of Sky Publishing. Any errors that may be present originate with the compilers of the data. At this time there are no plans to change data base."
"There are no maintenance manuals available. All aspects of the telescope's 'internals' are proprietary information and are not available; this includes the ROM format for the chips. All that is provided is the command set for writing custom software to operate the telescope."
I would like to save myself the effort of correcting it myself. I do not consider it at all difficult to do, merely an inconvenience.
>
> One other comment. Item number 4 refers to entering the correct RA
and
> DEC for Polaris for a given date. Aren't RA and DEC constant ?
>
Still haven't had time to adequately check this but I did run "Expert Astronomer" and set "epoch" date to various dates and achieve agreement with data posted by Jason Ware for a given date. Pretty sure that precession and nutation of earth's axis does affect the values so that you have to have the correct values for a particular date if your goal is accuracy and that is what this post is all about.
-------------------------------------------------------------------------
Have been pondering the postings regarding alignment star positions within the Meade database and believe I have figured out a work-around that allows more accurate Polar alignment.
I posted a message some time ago indicating that I had attempted to achieve convergence by repeating the Meade Polar alignment procedure several times. That was before corrected alignment star positions were posted. I now believe one source of the non-convergence was due to the coordinates for Polaris contained within the Meade object library chips. According to a letter I received from Scott Byrum at Meade, "The object library that we are incorporating into the LX200 was obtained and used with the permission of Sky Publishing. Any errors that may be present originate with the compilers of the data."
Since Polaris is the primary basis for polar alignment, we need in particular to establish its value with certainty. We also need to know the values for the other alignment stars with certainty because they are also used in the alignment process.
Anyway, once you have accurate right ascension and declination values for Polaris (Jason Ware posted Polaris coordinates of 2 28 14 and +89 14 44 for 16 Dec 94 as an example), below is a work-around for the polar alignment procedure using the wedge and version 3.30L of the Meade software.
1. Carry out the procedure for polar alignment given on page 31 of the Meade Instruction Manual. It involves centering Polaris using the wedge then centering a star chosen by the Meade software using the Keypad Hand Controller. Remember the name of the star chosen by the Meade software. Let's call it star "X". We will use it again in step 8 below.
2. Get into mode 2 (Page 38 of Meade manual for LX200).
3. Begin the procedure in paragraph "b." "GO TO Menu Option".
4. Enter the R.A. and Dec. of Polaris for today's date.
5. The Telescope will slew to the coordinates of Polaris.
6. Repeat steps 2, 3, 4, and 5. This is necessary because, for some reason, it doesn't always get it exactly right the first time. You can check the value displayed in the hand controller to see if the coordinates match the ones you entered. (You could make small pointing adjustments with the hand controller if necessary. At this point we want the electronics and gears to think they are pointing exactly at the accurate RA and DEC for Polaris.)
7. Center Polaris using only the wedge controls.
8. If star X happens to be an alignment star with little or no error within the Meade (i.e., Sky Publishing) database, press STAR, select star X, GOTO star X, GOTO star X again since the electronics, gears or whatever do not always get it exactly right the first time (at least that is what happens with my scope).
9. Center star X using the keypad, then press and hold ENTER until "COORDINATES MATCHED" is signaled.
10. Press GOTO to see if the star stays centered. Sometimes it does not. You may wish to repeat step 9.
11. Repeat starting from step 2 until convergence is achieved. By "convergence" here I mean that after step 6, Polaris is centered in your reticle and after step 8, star X is centered in the view field.
If star X was an alignment star with significant error within the Meade (i.e., Sky Publishing) database, then performing step 6 will introduce error. I do not see an easy way to compensate for star X errors.
By using the above procedure, I have been able to slew back and forth between Polaris and star "X" so that both stars are within 10 arc seconds of the center of the reticle. In particular, I have done that using Aldebaran.
Now, there is one problem remaining. Jason Ware posted data indicating that the Meade (i.e., Sky Publishing) Aldebaran coordinates are in error by 172.7 arc seconds. If he is correct, that would mean that we still have 172.7 plus or minus 10 arc seconds of error in the system. I do not see how to eliminate that error unless the database is is corrected.
It is my belief that the electronics and mechanics of the system are not the limiting factors for its pointing accuracy at the moment. Database errors in the 33 alignment stars are the limiting factor, i.e., the scope is much better than the database is allowing it to be.
-------------------------------------------------------------------------
Thanks,
Howard
From anderson Thu Mar 23 08:43:19 1995
To: lx200-l@netcom.com
Subject: Re: Meade GCVS errors -Reply
Content-Length: 2327
Status: RO X-Lines: 59
>
> Steven Ashe:
>
> Frank Farwell and I are collecting the posts on the accuracty of
the
> Meade databases. However, I must plead that I have not looked at
the
> GCVS since I do not do variable star work. I do know that there are
> numerous errors in the main list 250 stars. I also know that spot
> checking the SAO stars leads me to believe they have few, if any,
> errors. I guess will need to look at the GCVS as well. I had assumed
> that the errors in the main list were due to typos and that the other
lists
> were gotten in machine readable form (and hence fewer errors).
>
> I do know that the Meade calcuation of apparent postion is nearly
> correct (I don't know if they include aberation or not).
>
> My guess, by the way, on the error source is that Meade assumed the
> coordinates were J2000.0 when in fact they were B1950.0. I will look
> at this this weekend and e-mail you my conclusions on Monday.
>
>
> Ralph
>
>
Ralph, I hope you received my private post to you regarding polar alignment workaround procedure that I developed and have been using successfully. I did not receive an acknowledgement from you that you received that posting but I have held off posting generally here because you indicated you were compiling my work-around along with other information.
For what it is worth, I have done a cursory comparison of calculated positions of Polaris provided by several software packages I have bought.
With respect to the position of Polaris, I have ascertained the following values for the epoch date 1 Jan 2000 from various sources/software systems listed below:
SYSTEM RA DEC SOURCE
SAO Catalog
2 31 49 89 15 51
SAO
Expert Astronomer
2 31 50 89 15 51
???
MegaStar
2 31 48.7 89 15 50 Hubble Guide
Star Catalog
RedShift
2 32 46 89 16 01
???
Three of the sets of values above seem to be roughly in agreement.
RedShift appears be using the "NGC 2000.0" database by Sky Publishing (It is not entirely clear however). Scott Byrum of Meade said in a letter to me: "The object library that we are incorporating into the LX200 was obtained and used with the permission of Sky Publishing. Any errors that may be present originate with the compilers of the data."
Thanks
Howard
From anderson Thu Mar 23 09:21:51 1995
To: astrorcf@netcom.com
Subject: Re: Alignment work-around
Content-Length: 1714
Status: RO X-Lines: 46
> Hi Howard;
>
> I apologize for my very slow turn-around on this. But, I reviewed
your
> final post on the alignment work-around. I also ran it by the folks
at
> Meade since I thought their buy-in would be appropriate. The post
looks
> real nice. With all the talk about star errors again, this might
be a
> real good time to post it. I'll also put it on the LX200 WEB page
and the
> MEADE ftp site.
>
> THanks for all your hard work ....
>
> -Robert
>
>
Thanks, did you mean I should post it or you will?
I just posted something else globally regarding this. Then within 10 minutes, received your post. Hope my latest post was ok. The renewed interest brought it all to mind again.
Unless the positions of the 33 guide stars can be improved, there will still be a residual error equal to the error in the chosen non-Polaris guide star. I hate to go to all the effort of creating my own corrected ROM set but I am capable of doing so if necessary. I became an amateur radio operator when I was 14, have an MS in Mathematics, worked in the SPACETRACK system long ago developing software, have worked as a scientific software developer for 30 years, currently work with some of the brightest chip designers in the world, etc.
I would be very happy just to *buy* a corrected ROM chip set.
I am not sure what netcom.com is. What is your relationship with Meade? I am really happy with their scope and their whole system. It is unfortunate that the *database* is limiting its accuracy. It is something that can be very easily corrected. It is much easier to fix than a software bug. I believe they have done a superb job overall. Just need to provide a ROM upgrade.
Thanks
Howard
>From anderson Thu Mar 23 17:26:10 1995
To: lx200-l@netcom.com
Subject: Polar alignment work-around
Content-Length: 4803
Status: RO X-Lines: 107
In an earlier posting [Re: Meade GCVS errors] I must apologize for confusing Ralph Pass and Robert Fields. It was Robert that I have been working with regarding rewording the content of my Polar alignment workaround so that it would be suitable for inclusion in the FAQ or whatever. Sorry Ralph and thank you Robert for your assistance and acknowledgement.
Here is the information:
-------------------------------------------------------------------------
Have been pondering the postings regarding alignment star positions within the Meade database and believe I have figured out a work-around that allows more accurate Polar alignment.
I posted a message some time ago indicating that I had attempted to achieve convergence by repeating the Meade Polar alignment procedure several times. That was before corrected alignment star positions were posted. I now believe one source of the non-convergence was due to the coordinates for Polaris contained within the Meade object library chips. According to a letter I received from Scott Byrum at Meade, "The object library that we are incorporating into the LX200 was obtained and used with the permission of Sky Publishing. Any errors that may be present originate with the compilers of the data."
Since Polaris is the primary basis for polar alignment, we need in particular to establish its value with certainty. We also need to know the values for the other alignment stars with certainty because they are also used in the alignment process.
Anyway, once you have accurate right ascension and declination values for Polaris (Jason Ware posted Polaris coordinates of 2 28 14 and +89 14 44 for 16 Dec 94 as an example), below is a work-around for the polar alignment procedure using the wedge and version 3.30L of the Meade software.
1. Carry out the procedure for polar alignment given on page 31 of the Meade Instruction Manual. It involves centering Polaris using the wedge then centering a star chosen by the Meade software using the Keypad Hand Controller. Remember the name of the star chosen by the Meade software. Let's call it star "X". We will use it again in step 8 below.
2. Get into mode 2 (Page 38 of Meade manual for LX200).
3. Begin the procedure in paragraph "b." "GO TO Menu Option".
4. Enter the R.A. and Dec. of Polaris for today's date.
5. The Telescope will slew to the coordinates of Polaris.
6. Repeat steps 2, 3, 4, and 5. This is necessary because, for some reason, it doesn't always get it exactly right the first time. You can check the value displayed in the hand controller to see if the coordinates match the ones you entered. (You could make small pointing adjustments with the hand controller if necessary. At this point we want the electronics and gears to think they are pointing exactly at the accurate RA and DEC for Polaris.)
7. Center Polaris using only the wedge controls.
8. If star X happens to be an alignment star with little or no error within the Meade (i.e., Sky Publishing) database, press STAR, select star X, GOTO star X, GOTO star X again since the electronics, gears or whatever do not always get it exactly right the first time (at least that is what happens with my scope).
9. Center star X using the keypad, then press and hold ENTER until "COORDINATES MATCHED" is signaled.
10. Press GOTO to see if the star stays centered. Sometimes it does not. You may wish to repeat step 9.
11. Repeat starting from step 2 until convergence is achieved. By "convergence" here I mean that after step 6, Polaris is centered in your reticle and after step 8, star X is centered in the view field.
If star X was an alignment star with significant error within the Meade (i.e., Sky Publishing) database, then performing step 6 will introduce error. I do not see an easy way to compensate for star X errors.
By using the above procedure, I have been able to slew back and forth between Polaris and star "X" so that both stars are within 10 arc seconds of the center of the reticle. In particular, I have done that using Aldebaran.
Now, there is one problem remaining. Jason Ware posted data indicating that the Meade (i.e., Sky Publishing) Aldebaran coordinates are in error by 172.7 arc seconds. If he is correct, that would mean that we still have 172.7 plus or minus 10 arc seconds of error in the system. I do not see how to eliminate that error unless the database is is corrected.
It is my belief that the electronics and mechanics of the system are not the limiting factors for its pointing accuracy at the moment. Database errors in the 33 alignment stars are the limiting factor, i.e., the scope is much better than the database is allowing it to be.
-------------------------------------------------------------------------
Thanks
Howard.
>From anderson Fri Mar 24 13:17:13 1995
To: lx200-l@netcom.com
Subject: Re: Polar alignment work-around
Content-Length: 2237
Status: RO X-Lines: 50
> > Now, there is one problem remaining. Jason Ware posted data indicating
> > that the Meade (i.e., Sky Publishing) Aldebaran coordinates are
in
> > error by 172.7 arc seconds. If he is correct, that would mean that
we
> > still have 172.7 plus or minus 10 arc seconds of error in the system.
> > I do not see how to eliminate that error unless the database is
is
>> Drift method!
> > Jason Ware
>
The error between the true star X position and the telescope's calculated version of the star X position will continue to represent an error in the system. If you select star X, center it in the view field, then press and hold "ENTER" until "COORDINATES MATCHED" is displayed, the error between the correct and incorrect star X's coordinates would then represent the minumum error for electronic pointing achievable by the workaround.
I think that you are saying that the drift method can completely eliminate this error also, i.e., after doing the drift method, if you select and go to star X the scope will center on the true coordinates of star X and star X's displacement in the view field will be offset by the amount of the error. If you were to center on star X and do a coordinate match, the error would be reintroduced - so you don't want to do that.
Is that a correct interpretation?
I have focused on the work-around because I believe that I have demonstrated, to my satisfaction at least, that high-precision alignment (equivalent to the results obtainable with the drift method if my interpretation above is correct) would be possible by iterating on a slight variation of Meade's published Polar alignment method if the alignment star positions were correct. I believe the setup time would be less since there are built-in time delays with the drift method (you have to wait a few minutes to see what the drift is).
I have high hopes of eventually obtaining (or creating if necessary) a corrected database. Maybe I should string a line from my computer and drive the scope with somebody else's software and database whose data checks out just to see what happens...
Or I could use Antares as star X according to the data you posted previously showing Antares has only .03 minutes error...
Thanks
Howard
>From anderson Tue May 9 15:19:55 1995
To: lx200-l@netcom.com
Subject: Re: Fourth (and last) post on Meade DB Accuracy
Content-Length: 822
Status: RO X-Lines: 20
> There is, however, a workaround the errors for polar alignment ...
>
> Ralph Pass
Excellent work Ralph! I had not thought to check out the SAO list. I had assumed that we just had the 33 coordinates of the alignment stars to work with. I have been relatively successful with the workaround I posted several months ago wherein I mentioned that it was a definite improvement but that I did not see how to eliminate errors associated with the Meade selected star. You appear to have done it! Your solution is elegant. I will try it at the earliest opportunity!
Do you have an estimate for error that you are seeing with respect to the cross-hairs after the four iterations,. i.e., how close to center are you able to position the two stars when you switch between them after alignment is complete?
Thanks
Howard
>From anderson Fri May 12 08:56:52 1995
To: lx200-l@netcom.com
Subject: Re: Meade DB Accuracy Workaround
Content-Length: 2077
Status: RO X-Lines: 39
> I enjoyed the Ralph Pass post regarding a new accuracy
> workaround, but it did generate a few questions for me.
> First, steps 5 and 7 requests a double 'GOTO' push. Its not
> obvious to me the purpose of this step. I'm running 2.4,
> and I believe the second GOTO would effectively do nothing
> on my scope.
Cannot speak for your scope and version of software but in the workaround I published some time ago on this list, I indicated that I had to do a double 'GOTO' to get the scope to finally settle on the correct value. The first 'GOTO' got the scope relatively close but the second one caused a tiny bit more motion that was closer to the requested value. Subsequent 'GOTO's did not alter the scope's position further. The position readout on the controller does show the effect of the first and second 'GOTO' so I can see that the second does actually produce a correction. I would have believed the "second GOTO would effectively do nothing" before I attempted my alignment workaround but I found that it *did* do something.
Ralph's workaround is an improvement over the one I posted earlier because he uses the SAO catalog's coordinate values of the 33 alignment stars. The SAO catalog coordinates are apparently more accurate than the coordinates that were stored in the 33 alignment star list. Being a software guy, I had assumed that the 33 alignment star list coordinates would be linked to the SAO catalog coordinates but they are apparently stored separately and have different values? I have not had a chance to check all this out yet but it begins to sound reasonable...
The problem with the other workaround that you mentioned regarding getting coordinates from another source in my opinion would not work because you need to use the scope's SYNC process to cause the software to match the coordinates of an object selected from the scope's database. It knows what you selected and it knows what it thinks the coordinates of that object are. It will sync with respect to those coordinates and not to any external coordinates.
Thanks
Howard
>From anderson Tue Jul 25 08:36:36 1995
To: lx200-l@netcom.com
Subject: Re: Polar alignment
Content-Length: 6097
Status: RO X-Lines: 117
> Is there a way to use a second star of my choice rather
> than the second star the LX200 chooses when doing Polar alignment?
>
> Cliff
Yes. The iterative alignment procedure worked out by myself, Ralph Pass and others will allow you to do that I believe. I have been using this procedure very successfully and am able to slew back and forth between the SAO Polaris coordinates and the chosen SAO star coordinates so that both stars show up within seconds of the center of the 9mm eypiece's reticle crosshairs. (One of Ralph's major contributions, in my opinion, was the discovery that the SAO coordinates could be used to work around the Meade location database errors. Thanks Ralph!) Ralph summed the procedure up best with his "Fourth (and last) post on Meade DB Accuracy" which is as follows (substitute your choice of star in step 3 below...):
This is the fourth of four posts on the Meade location database errors. It would be nice to list workarounds for the errors for all the operational modes of the LX200. Unfortunately, the errors in the GCVS database and alignment procedures for AltAZ mode have no workarounds. They await the new ROMs from Meade.
There is, however, a workaround the errors for polar alignment if you have the 64K object library (e.g., ROM 3.3, ROM 4.2, or the library option for earlier versions). This is the subject of this post. The key is to use the SAO star locations and to manually do the alignment. Try the following steps:
1. Do two iterations of the normal polar alignment procedures. This means to select polar alignment, press GOTO instead of Enter on the first option. Note the Meade number of the star selected as the second star.
2. Tell the LX200 to use the SAO database (STAR, ENTER, UP/DOWN arrow to get to SAO, ENTER, MODE).
3. From the list of Meade numbers versus SAO numbers, find the SAO number for the Meade number found in step 1.
4. Repeat the following until you are close enough
5. Goto Polaris (STAR, 308, GOTO). After the beep, press GOTO again. After this beep, proceed.
6. Use the manual adjustments on the wedge to place Polaris at the center (I assume you are using an eyepiece with crosshairs, so Polaris should be under the crosshairs).
7. Goto the other star (STAR, <SAO NUMBER FROM STEP 3>, GOTO). After the beep, press GOTO again. After this beep, proceed.
8. Use the keypad controls to place the star under the crosshairs and when done, press and hold ENTER until a beep. The message on the display should say matched coordinates.
9. Repeat back to Step 5 until you are satisfied with the alignment.
Note: I am usually satified after four iterations starting at step 5.
Table of Meade number versus SAO number:
1 73765 51 77336 101 250885 151 N/A 201 228201
2 21133 52 196059 102 81298 152 225128 202 209163
3 91781 53 132444 103 43310 153 252853 203 122671
4 255670 54 132542 104 251006 154 83500 204 228420
5 215093 55 196240 105 251083 155 225128 205 209318
6 54058 56 113271 106 222321 156 8102 206 30653
7 21609 57 40750 107 156256 157 225335 207 142004
8 147420 58 58636 108 27876 158 225344 208 209696
9 11482 59 78135 109 15384 159 183139 209 209957
10 215365 60 196698 110 43629 160 140430 210 186681
11 54471 61 78297 111 81727 161 253097 211 142241
12 22268 62 151428 112 99512 162 225691 212 210091
13 232481 63 234480 113 251472 163 8220 213 186841
14 75012 64 95912 114 99809 164 29520 214 67174
15 248474 65 218071 115 28179 165 83893 215 187239
16 37734 66 78682 116 239689 166 225691 216 187448
17 75151 67 151881 117 180531 167 121157 217 67663
18 55306 68 249647 118 239791 168 253346 218 187600
19 308 69 234735 119 28315 169 183987 219 104461
20 129825 70 172676 120 157176 170 N/A 220 187683
21 216113 71 172839 121 251904 171 184014 221 187756
22 110920 72 173047 122 N/A 172 159682 222 18222
23 23789 73 218549 123 157323 173 141052 223 87301
24 38592 74 197795 124 240022 174 141086 224 48796
25 38787 75 173651 125 180915 175 184336 225 105223
26 39053 76 115456 126 251974 176 17074 226 125122
27 76199 77 218755 127 223603 177 184415 227 144150
28 256029 78 60198 128 223603 178 84411 228 163481
29 56799 79 N/A 129 138917 179 184481 229 49528
30 56840 80 115756 130 252019 180 160006 230 246574
31 149283 81 79666 131 240259 181 65485 231 230300
32 233564 82 174601 132 28553 182 253700 232 49941
33 94027 83 198752 133 63256 183 208078 233 70474
34 112106 84 175217 134 100384 184 208102 234 71070
35 57522 85 219501 135 181543 185 121962 235 19302
36 39955 86 235932 136 204371 186 244315 236 10057
37 170051 87 236232 137 28737 187 17365 237 145457
38 40026 88 117264 138 157923 188 160332 238 127029
39 131794 89 42630 139 241047 189 227707 239 164644
40 150237 90 220878 140 44752 190 102680 240 213374
41 131907 91 250495 141 224471 191 84951 241 145862
42 40186 92 236808 142 100766 192 65890 242 230992
43 132071 93 61414 143 224538 193 185320 243 255193
44 112740 94 236891 144 252582 194 244725 244 231258
45 77168 95 136871 145 182244 195 244726 245 90734
46 170457 96 237067 146 205188 196 208896 246 165375
47 132220 97 27289 147 100944 197 30429 247 191524
48 150547 98 81004 148 64203 198 228069 248 90981
49 132323 99 250695 149 225044 199 208954 249 108378
50 132346 100 98967 150 252838 200 102932 250 10818
Good luck
Cliff,
Howard
From anderson Mon Jul 31 12:44:24 1995
To: lx200-l@netcom.com
Subject: Re: Polar alignment -Reply -Reply
Content-Length: 234
Status: RO X-Lines: 9
> Cliff,
>
If doing an iterative alignment, it is important to only move the star
half the distance to the center on each iteration otherwise the alignment
will diverge. Someone posted that earlier, Ralph I believe.
Thanks
Howard
Copyright 1997, 1998, 1999, 2000
Howard C. Anderson
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