9 replies to this topic

[mikedent]

Hi all - basic question - I have ioptron Cem25p mount with the small illuminated polar scope through the mount base to use for finding Polaris and getting polar alignment. In this scope's "window" are red 2 circles, a smaller inner one and a larger outer one, with clock time faces. When aligning Polaris with its local time position, does it matter which clock circle is used, the smaller inner or the larger outer?? After I align Polaris, then I go to "Alignment" on the hand controller menu and use either "Solar System" alignment or "2 star alignment".

Also, when using Solar System alignment using planets, it seems to accept an alignment using only 1 planet, ie Venus, Mars, etc. Should it be asking for a second planet also for more accuracy? Or does the HC computer feel 1 planet is enough??

Thanks for your help!

[RajG]

The circles on the reticle have marked radii (36, 40, 44, etc). The hand controller (Menu -> Align -> Pole Star Position) gives the position of Polaris in terms of a "clock" and a "radius". Use the circle on the reticle whose radius is closest to that shown by the hand controller. See figure below.

 

[kathyastro]

Polaris is currently (2025) at approximately 89d16m declination, so it is 44' from the pole.  So you should use the circle marked 44'.  The inner three circles (36', 40', 44') are for Polaris in the northern hemisphere.  The outer three circles (65', 70', 75') are for Sigma Octanis in the southern hemisphere.

 

The declination of Polaris is gradually decreasing (i.e. its separation from the pole is increasing), so it is slowly moving out of iOptron's calibrated rings.  In future years, you will have to guesstimate how far outside the ring it should be.  The three northern hemisphere rings are 4' apart, which should help you guesstimate the position for quite a few more years.

Edited by kathyastro, 16 February 2025 - 04:10 PM.

[Martinbruce]

I don’t know if this will be helpful or not but I’ve used the free Iphone application called PS Align with my polar alignments. I checked the available Polar Scope Reticules in the application and the one that RajG posted is available to use.  The application knows all the presets , time, location and shows you graphically on your phone where to adjust your mount so as to line up Polaris. I will try to take a screen shot and post that for you. 

[Martinbruce]

Here is the screen shot using PS Align. Note the location on the reticule of where you should adjust your mount to position polaris. This just gives you graphically what your handcontroller also gives you. Good luck. 

[mikedent]

OK all, thank you all very much. Now I understand why there are 2 circles and to use the inner one, on its most outer circumference line.

 

Any info on using planet align vs 2 or 3 star align? I would think planet align would be less accurate?? thank you!

Edited by mikedent, 17 February 2025 - 01:53 PM.

[rjacks]

Aligning on planets is less accurate. Two stars is enough if you do a good job on the 2 stars. 

[triplemon]

Polaris is currently (2025) at approximately 89d16m declination, so it is 44' from the pole.  So you should use the circle marked 44'.  

Umh, that is the declination in J2000 epoch. While that is what you need to enter into any goto system or read on a paper chart, that is not what matters for polar alignment. For polar alignment you want to align to where the NCP is now, not where it was in the year 2000.

 

So you will want to use the declination in current equinox coordinates to determine the distance from the current NCP. That number is 89d 22' or 38 arcminutes from the pole.

 

And yes, some older reticles don't show suitable marks for that. These reticles are like me, old enough that precession notably changed since we were young. 3/4 of a degree was so much easier to memorize, I never thought I get so old that this isn't valid any more.

Edited by triplemon, 20 February 2025 - 01:24 PM.

[mikedent]

"That number is 89d 22' or 38 arcminutes from the pole"

 

So would I guesstimate another 6 arcminutes "in" from that outer 44 circle? So it would be a bit more to the center than the 40 circle, between the 36 and the 40 circles?? That would be hard to do accurately, but it's usually not 100% accurate alignment anyway...

[mikedent]

"So would I guesstimate another 6 arcminutes "in" from that outer 44 circle?"

 

Do I understand this correctly? Just a bit more to "center of circle" from the 40 circle?  Thanks for clarification...Mike