Quick polar aligning question

[cuivenion]

Once you've polar aligned your mount do you lose alignment if you stop the tracking. For example if you have only an RA tracker and you want to disengage it to reposition the scope manually using the control knob.

Can you polar align at 7pm leave the scope to cool and come back at 8pm start the tracking and still have good polar alignment. Sorry if this a daft question, it's something thats been bugging me.

[Tinker1947]

You Polar Align the Mount, the Scope is on a different section you could leave it a month and it would still be Polar Aligned....

[cuivenion]

Yeah, Thought I was being daft. Cheers for the reply.

[barkis]

Yeah, Thought I was being daft. Cheers for the reply.

Nothing daft about asking questions. There was something you didn't know, now you do.

It's how we learn much of what we know.

There is a saying often used on SGL, and it is true.

The only daft question, is the one you don't ask.

[cuivenion]

Best way to describe my thinking is, if you ali Polar Align your mount but Polaris is always moving how does it stay aligned? I just realised that the Celestial Pole doesn't move, so that answers my question lol.

[Ouroboros]

The way I think of it is that polar alignment aligns the axis of the mount to the earth's axis of rotation. 1,2,3 Star alignment then syncs the rotational position of the mount to the current rotational position of the stars to make GOTO work.

[brantuk]

Hate to spoil the party but the pole star actually does move - only in a very small tight circle - but so small and so far away that  to all intents and purposes a line drawn from it goes straight through the axis of the Earth from n.pole to s.pole. But in real terms it's just slightly "off-axis" - despite appearing to stay in the same place in the sky.

When polar aligning a mount using a polar scope (northern hemisphere), we see a central circle in the reticule and a tiny circle on it's circumference. It's the tiny circle we align the pole star to, ensuring when the mount RA axis turns, the star  stays  on the circumference of the larger circle - resulting in single plane right ascension tracking. Dec is taken care of by the Earth's spin once PA'd.

(I'll let you google "Earth wobble" and "Hour Setting" for further info)

[cjdawson]

I'm going to spoil the party a little more.

Firstly, I'm going to split the aligment into two seperate phases.

1. Aligment of the mount

2. Aligment of the software

Polar aligment of the mount means aligning the mount not to the pole star (or southern cross), but to the Celestial pole.  This point is about a moons width away from the polestar.  This is where the movement that Brantuk is talking about comes from.  Once the mount is correctly aligned to the Celestial pole, as long as the mount is not moved, you can move the OTA along the RA and Dec axis as much as you like and it'll remain aligned to the Celstial pole.

Alignment in the software however is a very different story.  On my LX-90, onces I've done the alignment process, I'd have to park the scope for it to remain aligned between power cycles.   On some more modern scopes, you can simple switch it off and on and it'll remain aligned.  On my Lx-90 I cannot loosen the RA or Dec knobs once it's been aligned as this will create a mismatch.  I have to use to the motors to drive to scope to the opposite side of the sky.   So in this respect, basically the scope has to be aligned pretty much every power cycle.  Again some scopes might have hardware that lets them know which direction they're pointing, so those scopes would be ok.    However, for my LX-90.  Basically, it's no, it doesn't remember the software alignment between sessions.