Another Polar Alignment Method

[Davelrkn]

Hi All
I was told many years ago that if you were to move the scope in RA and position Epsilon Crux and Beta Centauri so that they both passed through the centre field of view at the eyepiece you would be fairly accurately Polar Aligned as they both had fairly close Dec Positions of -60 degrees.

Last night I decided to test this method and used a crosshair eyepiece to obtain an accurate position when slewing the mount in RA,but used the finderscope for coarse positioning first and then for fine tuning used the recticle.

I found on my first pass that if was a liittle off and used the jacking bolts to fine tune and kept making adjustments until I had both stars passing through the crosshair.

I found that after I had done this I had very little drift in RA and was just a matter of some further fine adjustments with the jacking bolt to achieve extra no drift as you would carry out when using the drift method.

I did not have any drift in Dec as I have that set very accurate for my site from the drift method.

I then decided to test further away from the pole region and centred on Regulus and found no drift after 15 to 20 mintues of tracking.

I was very happy with the results and found this method equal to the drift method if not better as it was very quick and easy and took less than half the time when compared to the drift method.
As a suggestion when starting this method start at Epislon first as it is a lot easier to spot Beta that Epsilon when first slewing on those first couple of passes.

I would like to know if anyone has tried this method before as I have not seen anything mentioned before of using this as a method of Polar Alignment.

Give it ago a see how quick and easy it can be to obtain Polar Alignment.

Cheers
Dave

[Phil]

Very interesting. I don't have a mount at this point in time back down the track i shall give it a go.
Phil

[Davelrkn]

Hi Phil
I was not sure if this method would work but worked a treat
It's a great concept in that you can obtain a quick starting point and be close to Polar Alignment within a few minutes, by just getting both stars to pass through the reticle.
Cheers
Dave

[gmbfilter]

I'm keen to give it a go
Suits the way I'm setup
Thanks I'll keep posted

[bojan]

That figures.. Declination of both objects are almost the same (1 arc minute difference),

This method will work with any of pair of stars with the same declination. Preferably, the difference in AR should be 6 hrs or so.

[danielsun]

Thanks Dave, that is logical, simple and brilliant! :thumbsup: I have not heard of this method before but as soon as these clouds decide to part I am keen to try it out.

Cheers Daniel.

[Davelrkn]

Hi Daniel
I would be keen to hear how you get on when you get chance to get out under the stars
Thanks for your reply

Cheers
Dave

[tlgerdes]

Bojan has a good point, as those two stars, for at least part of the year, are not in a good position to see at the beginning of the night.

[telemarker]

This sounds interesting. I notice that you're already got the right alt setting. What about when both RA and DEC are out, not just RA?

[allan gould]

Nice one Dave -- sounds a quick and easy method to trial.

[Davelrkn]

Hi Keith
I am still looking into this method ,so far so good
I was able to get both Epsilon and Beta to pass through the recticle crosshair and feel it was because my Lat was accurately set from the drift method.
I will next knock my mount of it's Alt setting and see what effect this has when driving the mount in Ra when doing the passes and then make the adjustments to both axis to see if I can successfully get Epsilon and Beta to transit the crosshair as before.
When I first tried this method and had both stars passing through the crosshair there was very little drift in Ra and was just some fine adjustments needed with the jacking bolts to halt the drift.

Cheers
Dave
Ps I did reply to your post a few days ago but it never got posted

[Davelrkn]

Hi Allan
Yeah it is very easy and quick and have been able to achieve better than expected.I have searched the net to see if this method had been tried before but to no avail
Someone mentioned this method to me many years ago but was never tempted but kepted thinking about it over the years and thought I would give it ago
The guy never said that he had done it himself
Allan we have met before a few years ago at the GStar workshop
I have been the Moderator for the GStar Yahoo forum for the last three and a half years
Cheers
Dave

[pvelez]

I use EQMOD and Starry Night. Would I first do a rough 3 star alignment and then apply this method? Or would I simply switch, goto epsilon crucis, adjust with the controller to be centered on the star, slew in RA only to beta centauri and then adjust as you suggest?

Pete

[allan gould]

Dave
Nice to catch up and a great job you are doing as moderator.
Like the new method and as I said will give it a trial ASAP.
Allan

[Davelrkn]

Hi Pete
How are you?
You do not have to do a three star alignment first.
Just have the mount facing south as close to 169 degree as possible so that you do not have to move the mount if you run out of adjustment with the jacking bolts.You can if you like do a one star alignment on Acrux and align on it.
If your equipment allows user cord to be entered by your hand controller you can use the Ra & Dec for Epsilon to enable you to find easier.
I used the SAO Cat which Epsilon Crux is 251862 and as mention in my original post found it easier to start with Epsilon and slew in Ra down to Beta Centauri making adjustments with the Jacking Bolts until I had both Stars passing through the crosshair.
Once you have done the Polar Alignment you can then do your three star alignment
Hope this helps
Cheers
Dave

[Davelrkn]

Hi Allan
It would be good if you could check out this method and let us know your findingsn, but as be both live in Bris we both know how the weather has been here of late.
I know that I did not fluke being on the pole when I set up to try this method as I did check to see if I had plenty of drift before doing this method
Cheers
Dave

[toc]

I didnt have much luck with this - try as I might, I found no way to get both stars to line up, when just using RA movement. No matter how much I adjusted the bolts on either ALT or AZ. Is there something I am missing?

[Davelrkn]

Hi Tim
Please don't think I am questioning your experience here but can only thing I can think of is that you may not have selected Epsilon Crux the 5th star in the cross.I see you have a HEQ5 PRO which has the same controller as my EQ6 pro.I found it easier to do a one star alignment on ACrux and already had the Ra and Dec in the users menu for Epislon which I then went to it to start the first pass down to Beta Centauri (Hadar) .I found it a lot better to start with Epsilon when using the 12mm reitcle to make certain that I was on Epsilon.
I also made sure that I had the cross-hair orientated first as my 80mm refractor has little play in the draw tube and would cause an error in the alignment if moved during the procedure.
I also made sure I only used the Ra keys when doing the passes.

I am just about to go out and do some more testing and have knocked the mount off its Alt setting.

Cheers
Dave

[Davelrkn]

Hi All
Was able to get out to do some further testing with this method with mixed feelings.
I decided to knock the mount off its Alt setting and know that you may feel that I was a little extreme in using a rather large adjustment amount of 7 degree's but wanted to see what effect it would have on doing the passes from Epsilon to Beta.
I did mark my Alt on the Mount with some cloth tape under the Alt pointer so I could return to to correct setting.
I found that after I had made the Alt adjustment I was not able to get Epsilon or Beta to pass through the crosshair no matter what adjustments I made to the Jacking Bolts.I felt that the amount of mucking around with the adjustments you may as well carry out a drift alignment.

In saying the above I did find that when I did adjust the Alt setting and gradually returned it to the setting I had marked each time the behaviour of Epsilon and Beta became easier to centre on the crosshair.

I still believe that this method does work if you have your Lat set accurately like from the drift method and if like me need to take the mount out each time and setup in the backyard is very handy for quick alignment.

I have now tested on three seperate times in setting up using this method have been able to obtain polar alignment each time but only with accurate Alt setting.
This is still try and error as I there are no guide lines to work with as it's not a method that has been done before

Maybe there's a reason for that

Cheers
Dave

[toc]

Hey, I dont mind being questioned :)

I have the right stars - I double checked with 'starrynight' :lol:

Could it be a question of leveling? I use a bubble level normally, but I cant remember if I used it that night. Next time the sky is clear I will try again.

[Davelrkn]

Hi Tim

I don't believe that it would be that critical for the mount to be dead set level but also depends on how far you were out when making the passes.
Last night I went out and did some further testing, see my last posting.
I feel it's more likely to be Alt position as I found this can really play havoc with this method when testing last night.
Once I returned the Alt back to the setting I originally had I was able to get Epsilon and Beta to pass through the cross hair.

Cheers
Dave

[toc]

I think your right - yesterday I WAS able to get them pretty close - or at least in the center of my telrad. I had a lot of trouble getting it dead center of a reticle though.

[danielsun]

Hi Dave, I tried this method tonight and it works.:thumbsup:
I aligned both stars and checked my polar scope and there was octans, slightly off though my mount was a little off level but still very close. :thumbsup:


Cheers Daniel.

[telemarker]

Dave, I tried this method tonight and my mount was way off when using the crosshairs on the finder (on both the Alt and Az settings). What I did do though was to adjust one star with alt, move to the other and adjust the azimuth. By moving between the stars and adjusting only one setting at each of the stars, I had them passing through the crosshairs on a RA traverse in a couple of minutes. I'll try this again soon to see if I can replicate it.

[bojan]

This is a correct way to do it.
However, the method will converge faster if you do polar axis elevation correction on whichever star is lower or higher in the sky.
The azimuth of the polar axis is then done on the other (whichever is more to the east or west).

Ideally, the stars should have RA difference of ~6 hours... and at the time the alignment is done they are positioned in the sky such that one is exactly above or under the SCP and another one to the left or right.

BTW, this method of polar alignment is exactly equivalent to the use of polar scope, except the above mentioned stars are much brighter than Octans stars and the accuracy could be better if higher magnification eyepieces were used. However, to achieve the maximum accuracy, the DEC difference between the two stars (01'40" or ~1/20 of Moon diameter) should also be considered and eventually corrected.

[Andrew C]

another pair of bright (mag 2) stars that are close in DEC (1'51" apart) and meet the 6 hour criterion are:

mirzam in Canis Major (west of Sirius) and diphda in Cetus.

I'll try them out when the rain stops in Alice Springs!

[telemarker]

Thanks for the explanation Bojan. Sort of puts the method to my madness :P

That's interesting Andrew, handy to know. Might look to compile a list of pairs to use later in the year while the cloud is hanging around.

[bojan]

This way of thinking could be extended a bit further, by designing a special reticle with double cross-hairs in the eyepiece, positioned such that the difference in DEC for specific stellar pair (and specific telescope FL) is accounted for.
In this case, the pair does not have to be exactly at the same DEC, as long as it could fit in the same FOV.

[Davelrkn]

Hi Everyone
Thanks to all those that have given this method a try and posted ideas suggestions.
Daniel glad to hear you have had some success with this method.
Andrew will have a look at the two stars you mentioned and give it ago when the clouds part here in Bris.
Bojan that's interesting you saying that this method is equivalent to the Polar Scope method, never thought of it that way but you right.
I found the other night it was a lot easier to find Epsilon by doing an alignment on Acrux and by moving the scope in Dec to the North, Epsilon came into view of the finderscope.

Cheers
Dave

[PeterEde]

Has this thread died a natural death.

May have to give this method a go tonight if the clouds piss off

[Regulus]

Thx Peter, I am glad u bought this thread back to life, it was so interesting.
The first I have heard of it and Bojans suggestions of eps for different star sets was good too.
Trevor

[PeterEde]

I need a cross hair reticle but last night I used my camera's live view. It was late and I cant see stars near the horizon. Probably nearer 40 deg high.
Will give it another go tonight. Earlier I at least got a star to follow vertically.

[John K]

Guys,

I am always looking at different methods to quickly polar align.

My scope is slightly different - it's on a horseshoe equatorial mount without GOTO.

If I assume that my latitude adjustment is fine, how would it work with my mount?

Image of scope here:

https://www.flickr.com/photos/johnkazanas/176154968/in/set-72157594183210993

Complicating matters, the scope has a rotating truss nose.

John K.