Polar scope thingy

[thing]

On my CG-5 mount there's a basic sort of polar scope built into the mount. It's barely useable but I gave it a go last night after a course in yoga..........I noticed that on the crosshairs (which are invisible at night naturally........) there's a circle on one of them, anybody any idea what it's for?

[Andrew*]

you put polaris in that circle...

[thing]

I half guessed that but being as the circle rotates with the eyepiece focusser which way up should it be? Does the circle go to the top or bottom? I take it it's there to get the proper compensation for true north. You can't see it in the dark anyway so it's a bit academic. I just have a need to know these things........ 8)

[Andrew*]

you know, I have no idea! I just put it in the circle whatever time of day or night or year it is! :?

It's just struck me that with the HEQ5, the plough and cassiopeia are also marked on the polar scope, so you're meant to rotate the scope to match with the star positions.

With other polar scopes, I guess you just have to learn where polaris is in relation to true north. Use a star map or something...

Abdrew

[thing]

A star map, now why didn't I think of that. Thank you sir.

[Sam]

This is what is really useful about this forum, I learn something every day! Andrew comments about the HEQ5 make quite a bit of sense as I have been wondering if the polar scope is supposed to rotate or not. The only problem is when lining it up I can't see any of the markings on the polarscope, so I'm quite sure why they printed them.

Sam

[steppenwolf]

HEQ5 and EQ6 owners might find this article on my website useful to explain how the PolarScope works - In fact, the instructions for the HEQ5 should also apply to the EQ5 and EQ3-2 as well:-

http://home.btconnect.com/astro-site/polar_alignment.htm

[Sam]

Thanks for that - this stuff just gets more and more complicated :?

[Tinkerbell]

If You can't see the markings on the polar scope reticle try shining a red torch across the top opening and like magic the markings appear. If you can find Kochab you can use its position to place Polaris in the polar scope. If Polaris was at the center of a clock face and you can find Kochab then that position translates to where Polaris should be in your polar finder. At 18:00 tonight Kochab will be at roughly the Eight o Clock position so in your polar finder you would position Polaris at the eight o clock position and then do a drift alignment if needed. Have a look on any planetarium program for the two stars mentioned and draw a line between them and you will find that Polaris is on the opposite side of the NCP (Northern Celestial Pole)to Kochab so that the center cross on the polar finder and the position markings for the placement of the pole star correspond to this difference. Try this link it explains it in full < http://www.weasner.com/etx/ref_guides/polar_align.html > After you have tried this a few times it becomes easy to polar align.

Hope this is of some use.

[Sam]

Thanks very much for that information, Looks clear at the moment so I should be able to give that a go.

Sam