Moving the telescope after polar alignment

[mrjonathanbrown]

Hi guys at SGL. I have posted a couple of related threads in the past regarding polar alignment (How to) and the difference between drift alignment and polar alignment. I feel I am more confident in how to polar align especially how EQMOD helps so much and Backyard EOS for drift alignment plus lots of youtube tutorials. 

Anyways I have not yet had a chance to get out with the newly purchased mount (HEQ6) weather has been well horrible as most of us know (I can certainly speak for Glasgow) - Well I know how to polar align (well at least I feel confident in knowing how to) Im having difficulty understanding how I move the mount (scope) after polar aligning - I understand your aligning the mounts RA to the earths axis but why is this if after polar aligning and you slew to a object in the sky you are then maybe having to move in RA/DEC? 

Im a little confused not sure if this has anything to with my lack of sleep.. been working all night  

[Merlin66]

The "polar" axis, the RA axis, is aligned to the pole using the altitude and azimuth screws on the base of the mount.

If it's aligned, then in theory (!?) the axis can rotate 360 degrees and still be aligned with the pole.

This movement allows you to track a celestial object just by driving the RA axis.....

Hope this helps.

[valleyman]

There are basically 3 parts to the mount.

1st part is fixed onto the Tripod. This is the part that is polar aligned using the RA and Dec screws. Once this is aligned it does not move.

2nd and 3rd parts are the RA and DEC axis which move separately allowing the scope to move to any location without upsetting polar alignment.

Pat

[brantuk]

You'll find that once polar aligned you can point the scope in any direction N/S/E/W just by loosening the clutches and swinging the scope around - but make sure it is well balanced first for best control. As Merlin says - once you lock onto an object it can be tracked in RA only. Depending on how close your PA is it may need minor adjustments in Dec. This will become apparent by object drift in the eyepiece when observing - or blurring/trailing of stars when imaging. Hth

[ultramol]

The penny dropped for me when my brain realised that you are polar aligning the mount and not the telescope !!! It does not matter were the telescope points as long as the MOUNT is polar aligned . I hope this helps as I had sleepless nights trying to work it out. I know that there is a lot more to it but this realisation helped me to get there in the end..

[mrjonathanbrown]

Thanks for all the responses I have one more question on my mind when polar aligning through the polar scope your aligning your mounts RA in relation to polaris's transit time correct? Does this mean after polar aligning you only use DEC Axis? Im finding it difficult to understand if you were to slew to a celestial object after alignment your mount would move in RA/DEC (Depending on where the object is in the sky) but lets say the mount has to move in RA/DEC how can the alignment still be held? 

[mrjonathanbrown]

Il keep reading over the comments until it sinks in the answer might be right in front of me I'm just not clicking straight away. 

[RichM63]

The base of the mount does not move in DEC after PA, only the telescope head can swivel independently of the aligned base.

The RA rotates around the polar axis not side to side through it.

Remember celestial movement that we 'see' is in arcs not straight lines hence the requirement to have the scope move in such a way that it can follow an arc at the business end.

After good PA, you can use the DEC axis for slewing to target but hopefully you wont then need to touch it.

Manual or motor tracking is all that is then required to compensate for the movement of the Earth with the RA side of things.

We are not still, but are spinning and also orbiting,it just so happens that in the Northern hemisphere we have a handy NSP that remains fairly constant from our position on the planet.

Lousy explanation, but this is how I understand things.

What I don't know is how do they align for tracking from telescopes in space, I'm stuck on that one.

Best,

Rich

[Astro Imp]

Thanks for all the responses I have one more question on my mind when polar aligning through the polar scope your aligning your mounts RA in relation to polaris's transit time correct? Does this mean after polar aligning you only use DEC Axis? Im finding it difficult to understand if you were to slew to a celestial object after alignment your mount would move in RA/DEC (Depending on where the object is in the sky) but lets say the mount has to move in RA/DEC how can the alignment still be held? 

Your mount doesn't move once you polar align, it's the telescope that moves.

I know it does your head in to start with but once the penny drops all becomes clear.

I would suggest that you set your mount up in daylight and do a "dummy polar align" (point north using a compass and set your declination to that of Glasgow. Now move your telescope using the RA and Dec controls. Watch what happens to the mount. it doesn't move.

HTH

[mrjonathanbrown]

I appreciate everyone trying to help me out I feel almost daft for not clicking on haha. The bit that confuses me still seems to be when initial alignment using EQMOD polar alignment get polaris in the crosshairs of the polar scope then using latitude bolts get move polaris to 12 O'clock position then click "Align polar scope" EQ ascom then moves the circle in your polar scope to the exact position of where polaris should be (using the RA motors) then you adjust your altitude bolts/azimuth bolts to get polaris in that circle hey presto polar aligned. Why move the RA for alignment if its going to be moved once slewing to an object? 

[ultramol]

When the mount is polar aligned then wherever you put your telescope in RA and lock it, it will track the sky that its pointed at (well it will if you do a good polar align ) . The time bit of were polaris is is just a known starting point that you need to make sure the bit of sky you are looking at does not wander off. I got this info only last week of WAVESOARER on this forum and I followed his instructions and when I tried it out my tracking was as near perfect as it could be. He said

1 Get polarfinder off the internet and put your details in

2 print the time you want to align your scope

3 Go out and looking through your polarscope match the image with whats on your print out using the latitude and azimuth bolts to get polaris onto the circle. It does'nt matter if its not in the little circle as you are not using your setting circles

4 Rotate the RA axis and watch if polaris stays on the circle when you turn it

If it does then you are there.  If not then fine adjust with the bolts till it is.I know this is not good enough for long exposure photography but short exposure is fine and slowly you will start to understand what is going on but in the meantime you can start to enjoy what you are doing instead of going out of your mind (Been there and done that )

I know with practice I will get better and understand a bit more as I go on. Hope ypu will too

Regards   Geoff

[chrisshillito]

Why move the RA for alignment if its going to be moved once slewing to an object?

The RA axis is moved during polar alignment only to put the polar scope reticule in the correct position for you to use the alt/az bolts to align the mount itself.

You don't have to move the ra axis, you could just adjust the az/alt bolts until polaris lies in what looks like the correct position on the reticule circle - however doing that requires a certain amount of guestimation which can be reduced significantly by letting eqmod position the reticle bubble in just the right place by rotating the ra axis.

Once you have the mount polar aligned just move it back to your normal starting (home) position and initiate gotos (and goto alignment) from there.

Chris.

[mrjonathanbrown]

@chrisshillito I think its all starting to sink in now - Im taking a wee break just now Il take the time just now to say thanks for thos tutorials on youtube!

[mrjonathanbrown]

@ultramol Big thank you as well mate appreciate your help! 

[tammclaughlin]

Just want to add that I was confused as to how you use the telescope after polar alignment despite reading and watching a few videos.

I came across this yesterday and the penny dropped!!

I thin the problem I found was that some documentation or videos would describe how to do one specific thing rather than take you through the process of setting up and then using the telescope so it came across as disconnected.   Maybe there are better videos out there but at least this forum got me on track.

Thanks.

Tam