Improving Polar Alignment Without Using Polaris

[London_David]

I recently purchase my first EQ setup. And as you might guess... my biggest issue has been polar alignment. I have some big constraints, but I've worked out a solution. The question is:

Does anyone have any suggestions for improvements in set up speed or accuracy, given the constraints of: no pole star and only 15 degrees of sky (pointing south)?

Why the constraints?

I’ve not got an optimal location. That's putting it mildly. My observatory is the bathroom... and my dome opening: the bathroom window. I can only see a thin sliver of the sky, about 15 degrees of sky looking south. So, no pole star and it rules out easy software alignment like Alignmaster. Also, no wide view for two star alignment for the GoTo afterwards. 

After much searching the internet I figured I could align the mount using an inclinometer as you would for solar observing. I'll go into detail on what I do to see if there's something I could improve. 

Before you start know your observing lattitude. Your phone gps is okay, I think dropping a pin on Google maps is better, because phones can sometimes give inexplicable readings if they don't get a good signal. Also, the inclinometer I use is rated to 0.05 degrees (DigiPas DWL80Pro £35 on Amazon). 

This is a slightly modified version of (https://www.cloudynights.com/topic/416367-daytime-polar-alignment/), and learning stuff from this video (https://youtu.be/rPdQ9pU9GJA) and this one (https://youtu.be/AAB9nom4Ke0). I may also have modified it for the worse so please correct errors or redundant steps. 

Here’s what I do:

- Set up and roughly align the mount and North using a compass.
    - On the EQ3, one tripod leg is marked N and you just point that north.
    - Precise is great because it makes things quicker, but it doesn’t matter too much at the moment — you only need to be precise enough to be able to compensate later with the RA knobs.
    - The easiest is to figure out the west-east axis and put the back two tripod legs on it. 
    - iPhone compass is fine.
    - Make sure the compass is set for true north, not magnetic!
    - Level the mount using the spirit bubble on the tripod. 

- I double check the finder scope is pointing in line with the OTA using any bright object. Important for later.

- Register the OTA position to the mount controller, (this will mean the alignment works even if your mount isn't properly levelled, or starting in the home position). 
    - North/South register
        - Move the mount to point North exactly north on the horizon
            - I use SkySafari and move the reticule until it points exactly north. 
            - I've set up a UserDefined mount park on EQMod for quick goto then tweak the last fractions using slew controls.
        - The OTA should be horizontal on the west side: parallel to the ground pointing directly north at the horizon.
        - The counterweight should be horizontal: parallel to the ground along the West-East axis. 
        - Release the relevant clutch and level the counterweight arm using the inclinometer (you will get the best reading with the level instrument as far away from the mount fulcrum as you can). 
    - West/East register
        - Move the OTA to point exactly West on the horizon.
            - I use SkySafari and move the reticule until it points exactly west. 
            - I use the UserDefined mount park again on EQMod then tweak.
            - The counterweight arm should be vertical at an angle of the arm at about 90 degrees minus your latitude. The arm will be lining up north-south.
        - The OTA should be horizontal: parallel to the ground pointing west. 
        - Release the relevant clutch and level the OTA using the inclinometer. 

- Align the OTA in Dec
    - Point the OTA exactly north at the horizon.
            - I use SkySafari and move the reticule until it points exactly north. 
            - As before I use the UserDefined mount park on EQMod for quick goto, then tweak until perfect. 
        - Again, The OTA should be horizontal on the west side pointing north, with the counterweight arm parallel to the ground on the east side.
        - I use the park position and then slew the reticule on SkySafari to make sure it's lines up with the mounts model. 
    - Level the OTA -- this time using the Declination polar alignment bolts.
    - Do not release the clutches.

- Align the OTA in RA, and correct for inaccuracy. 
    - Turn on sidereal tracking.
    - Slew to any bright object you can see.
    - Do not de-clutch the scope.
    - Center your bright object in your finderscope eyepiece using only the physical RA polar alignment knobs. Dec should be close to correct.  
    - Ideally you will only be adjusting RA, but you will probably want to tweak Dec a little too.

- For final tweaking, centre it using the polar adjustment knobs in your highest power eyepiece too.

- Focus using the Bahtnov on the bright object (though it could be any star) using the ASI290 on the screen.

- If this is not good enough then drift polar align using the camera which has a good explanation of what to do here: https://www.cloudynights.com/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760

- Here too:

 

 

It seems not many people outside of solar observing do this - or at least if they do they don't talk about it!

This procedure uses the fact that the equatorial mount has be exactly level to point exactly to the West or South cardinal point on the horizon. From that you can get your mount and sky model aligned, then you can align it to the sky. 

It took me quite some time to figure this out, because instructions I found didn't quite seem to match my setup - nor really explain why something was happening. Hence why this is a little over explained. As a beginner I was very unsure about a lot of things that now seem obvious.

I've found this a very easy way to polar align without going near a polar scope or Polaris. Visual is great with the procedure, now I'd like to tweak to see if there's a way to get longer exposures without a drift align, i.e. over 30 seconds on an f5 Skywatcher 150pds which is 750mm with an ASI290. 

Also, since I’ve not really got the space to properly align the scope for the GoTo to work as well as I’d like, this works well enough for small goto jumps after the initial align. EQMOD software can build up a sky model with the jumps and I find it accurate enough within my viewing window.

This is basically star hopping with GoTo: align, star-hop, align, star-hop, align. It’s actually quite a fun way to get around and is relatively accurate straight off the bat, especially since I’m only looking at a small part of the sky.

Does anyone have any suggestions on how to improve speed or accuracy in this procedure, within the given constraints?

[ronin]

My problem is you are talking of aiming the OTA at things and you should be aligning the mount, the OTA is at this stage a bit immaterial. You can (and many do) perform the polar alignment without the scope on the mount.

You could find that Skysafari uses magnetic North so that is innaccurate but only to a small extend, about 1 degree. Reasonably sure of this as the case for mine is magnetic and SS5 changes the direction of North depending on where the case clasp is. Never understand why with GPS it still uses a magnetic sensor in the tablet and then why SS5 uses this magnetic interpretation either.

Because the OTA and the mount are independant I cannot really see where the mount polar alignment is done. The section at the end "Align the OTA in RA, and correct for inaccuracy. "  seems to be centering the object in the scope, there appears nothing to sync the mount to the position. 

One way of looking at this is: If you set the polar alignment as best you can by Level mount, Polar scope pointed true North, Latitude set to 51.5, then put the scope on and deliberatly set the scope at 5 or 10 degrees off from the mount axis would you reduced the polar alignment innacuracies. Just the presumption that the mount and the scope point at the same thing is incorrect, although very common. You polar align, then lock it at that setting, you then have a scope and you swing that all over the sky but the polar alignment remains fixed, it does not follow the scope. If you cannot alter the scope from True North then how do you swing it South to look at Jupiter.

[newbie alert]

You say you only have 15 degrees of sky pointing south...

How can you then point west?

Maybe load it in the car and have a better fov

[Juicy6]

Buy a cheap digital inclinometer from China and bolt it to a dovetail. With this mounted instead of OTA and together with a good compass, you will end up within half a degree from NCP. Then use DARV, Drift alignment by Robert Vice, in PHD2.

 

 

[Cosmic Geoff]

I don't think that you will get much satisfaction from trying to observe out of a bathroom window. Just my opinion, but I don't think it's even worth trying to set up an equatorial GoTo in that situation. Warm air from the building will distort your view.

You really need to take it outside, either to the flat roof, or somewhere at ground level where you can observe without being bothered. Perhaps you can find a local astronomical society which holds viewing nights.

[London_David]

Hi Ronin, just to clarify --

You could find that Skysafari uses magnetic North

The SkySafari app has no sense of direction in this system. It only shows the model of the sky that the mount is using. The first part is aligning the mount to the model, so I could physically move the mount anywhere and SkySafari would never know. But the model in sky safari and the mount would match. 

Because the OTA and the mount are independant I cannot really see where the mount polar alignment is done. ...

The section at the end "Align the OTA in RA, and correct for inaccuracy. "  seems to be centering the object in the scope, there appears nothing to sync the mount to the position. 

As I understand it, the alignment happens in RA mainly when I place the tripod down in the correct orientation, then accuracy increased when I move the mount with the knobs to point at an object I know the location of in the sky. I do not slew or unclutch, I move the mount to align the mount with the model of the sky the mount has in the computer. In Dec, alignment happens mainly when I level the OTA at the horizon pointing north using the mount adjustment. Then accuracy increased when centering on an object, similarly this is physically moving the mount to align it with the computer model the mount is using. It's the reverse of a "normal" pocedure: polar align the mount first, then star align. Here, I align the star model with the mount, then I align the mount and it's model to the real world.

You could indeed do most of this without the ota off, but with the ota and the inclinometer, it is easier to get a reading further away from the fulcrum. I don't think you could fine tune as close since I'm not using the polar scope.

 

 

@Cosmic Geoff -- actually I've had some great views out of the window, and I'm in zone 2 London so light pollution is a pain too! I'm most interested in EEA for DSOs. It is best when you let the room cool and, yes I have to wait for the sky to come around... but it forces me to observe deep into the area I can see. And, dare I say it, an edge of excitement since if I don't get something right, I might miss it for the night  

 

I am most interested in galaxies, but the moon and Jupiter also wander past the window too. I do get out of my home observatory once or twice a month to local societies observation meetings since the setup is small and portable. But I'd rather try to see stuff if the clouds suddenly clear just taking 20 minutes to set up in the back than have to wait for a society meeting and hoping for good weather!

 

@Juicy6-- thanks -- I read about Darv ages ago but haven't tried it. Totally forgot about it. 

Also -- I have the inclinometer and the dovetail  already -- excellent idea! I will see how much faster this is, roughing it without the ota, then switching to Darv for accuracy. 

[Juicy6]

...and when you found good PA setup you might do something like this and you can repeat in minutes:

My laser aided PA