TheSkySearchers

Several days ago I used this simple method to find back the best position of the polar axis without the aid of apps, polar finders or even planisheres. The old position was lost as a result of the "help" of some enthusiastic amateurs who weren't aware of the mirror flip our old observatory telescope makes and started turning the altitude and azimuth knobs of the mount.

The method originates from the old days. In those days I had no apps or polar finder. Just a map of the environment of Polaris.

1. Take care that your finder is good aligned with your telescope
2. Put the mount in the park position. With the counterweights down and your latitude scale in the right reading of your location.
3. Put Polaris in the finder, while using Altitude and Azimuth knobs only.
4. Look in the main scope with your lowest magnification, Polaris should be in the center. Prism or no prism, no problem. Field of view in my case was 0,8 degrees, roughly as much as the yellow circle in the image. Having a field of 1,2 degrees is more than enough.

Now it really starts. 6. Look for the star pattern that is shown in the pic. It should be in the same field. The stars are connected with a yellow line in the image. This is a bit harder than it seems. It is quite easy to take by mistake almost the same star pattern as shown in another corner. ( here left and up)

7. Note that star Mv8.1 and Mv10.4 in the pic are 13 arc minutes separated, and the true North pole is another 13 arc minutes away. Those two stars show you the way. I drew an imaginary red triangle just for help. 8. Put the estimated spot in the middle of your field of view by turning the altitude and azimuth knobs of you mount. Stay away from RA or Dec.

9. Bob's your uncle. The true pole is less than 2 arc minutes away, more accurate than usual every day polar finders. Checking with star-drifting at 400X resulted in a drift of a few arc-seconds / time-minute.

10. If necessary you can complete this alignment with the star-drifting method for photography. But that is another cup of tea.

I like this method, and I have used a similar method to polar align my C-90 on its wedged fork mount. I think somewhere in there should be a determination of where the RA axis is pointing. As written, this method is only as good as the accuracy of your home position and your latitude scale.

Finding the centre of rotation in the field of view could be done with reference to a reticle eyepiece, or you could just eyeball it. It's the centre of rotation you want to place in the illustrated position, not the centre of the field of view.

If this is old school then I must have re-invented it a few years back! That asterism is exactly the one I "discovered" a few years back.

I refer to it as the "coal scuttle" (kolenkit in Dutch) and use it for astrophotography polar alignment, no computer or polar scope needed - just a DSLR and a piece of tape with a pinhole in it. Here's how it works:

https://www.youtube.com/watch?v=m52HFBUS0RQ&t=86s

Or, perhaps a bit clearer, in this PDF that I presented at the RTMC 2017 in the 5 minute show-and-tell sessions:

I use that asterism also for visual polar alignment if I am in a nerdy mood.

1) Make sure the scope has no cone error. This can be done in the daytime by rotating around RA and making sure that the rotation is around the center of the FOV, by adjusting the OTA mount screws as needed.
2) Find the DEC position such that a slew around RA shows the stars going around in concentric circles with their center at the center of the FOV. This means that the scope's optical axis coincides with that of the RA axis. This can also be done in the daytime without stars, just like with (1). In fact if your eyepiece has cross hairs and the LED batteries are not working (as usual), it's better. I usually do this with both clutches mostly disengaged, that works the easiest for me.
3) Using the Alt/Az knobs only, move the NCP to the center of the FOV.

If all stars needed for this are outside the FOV but if the mount is level, set the Alt setting circles to your latitude first then a turning the Az knobs should reveal Polaris fairly easily.

Thanks for your contribution.
I didn't know the asterism was referred to as "coal scuttle".
Glad to see the old art of polar aligning has not been completely repressed by fancy apps and programs. Just a keen eye and a telescope will do.

John Baars wrote: ↑Sat Sep 12, 2020 11:07 pm Thanks for your contribution.
I didn't know the asterism was referred to as "coal scuttle".

That's just the name I gave it because it did not have a name, and it looked like one!