EQ mount questions

[Radar2312]

Hi all,

Sorry if these questions seem dumb, but a couple of things got me stumped -

recently acquired an SK80 on an EQ1 tabletop mount as a Holiday scope and ultimately, use the scope for auto guiding on my HEQ5 Pro and maybe use the mount for my camera and some wide field shots.

I started out with an Alt/Az tracking mount and deciphering the celestial 'co-ords' of objects from stellarium was easy peasy (on the few occasions we had some clear'ish' skies)

Even though I have the full goto HEQ5, I figured a few sessions with the EQ1 would help me get familiar with the principles of the equatorial mount. So ......

1) what should the setting circles show in the 'home' position (pointing at Polaris with OTA on top and C-weight shaft pointing down)? Having read a file on the internet and cross checking the EQ1, it seemed to be 'roughly' correct. However, when slewing the RA/DEC around to the RA/DEC values from stellarium, I ended up in some really strange positions and often pointing in what was obviously, completely the wrong direction.

2) My basic understanding of RA/DEC is that once you are polar aligned and set on an object, said object travels across the sky (effectively) in the RA axis only, hence being able to track using only 1 motor drive. What confused me here was, I noticed on Stellarium that once I had selected an object to find its RA/DEC position, those values were not changing, even on 'fast forward'. As I said, I was not expecting the DEC value to change but I WAS expecting the RA to change in line with the passing of time.

Any and all input welcomed with open arms

Clear skies to you all

Rick

[brantuk]

The RA/Dec doesn't change - I think of it as a fixed grid on the sky (globe shaped) - the Earth spins within it. The only thing that changes is the Earths position and your position on it. Alt/Az however isn't polar aligned - so both axes change as the Earth spins. When your equatorial scope mount is polar aligned it simply counteracts the movement by turning in the opposite direction (in one plane) thus keeping it pointing at the same point on the grid.

[Radar2312]

ahh, ok, think that explains it. I had assumed, as humans so often do with many things, that RA centred on us!

This would also explain another piece I read explaining that, after polar alignment, you then need to find and easily identifiable, bright star, centre on it, and set your RA circle to the correct setting for that star and, hey presto, you're away!!! (yes??)

Think I'm getting the hang of it.

Cheers

[PorkyB]

To visualize it, display the EQ grid in Stellarium and set the time to fast-forward. You will see the EQ grid is moving in relation to us but stationary in relation to the stars. The opposite is true of the alt-az grid.

For a relative beginner like me, Stellarium's EQ grid is also useful to show which way my scope will move when I twiddle the controls.