Another star adventurer alignment question...

[Mr niall]

Hello!

now I’ll just preempt this by saying I am using the PS align app and all is well but... I’ve made the mistake of reading the manual - and those little twiddly numbery things around the polar reticule annoy (I don’t like having things and not knowing what they do or how to use them!) me and I’m determined to figure out how to use them. Now I’ve managed to correctly calibrate the reticule and the alignment but there’s a step in the procedure for aligning the dials that might as well be in Russian as far answer I’m concerned. Can anyone help?

[newbie alert]

To align my S.A. I have the clock face as it is and make sure if I put Polaris on the 3 o clock to 9 o clock line and turn the knobs on the side it stays on the line.. I simply place Polaris where it should be and unless I'm heavy handed or knock the camera I get what ever length subs I need.. maybe a crude method but not got the manual as mine was secondhand

[Davey-T]

If in the UK I would think 0 as UTC / Greenwich Meantime would be good enough.

Dave

[Mr niall]

8 hours ago, Davey-T said:

If in the UK I would think 0 as UTC / Greenwich Meantime would be good enough.

Dave

That’s what I assumed - turns out my Russian isn’t too bad!

do you have any idea where the -120 degrees is the instructions came from though (just out of interest)

[Mr niall]

Ok - looks like I’ve gone wrong somewhere can anyone help? Following the instructions I’ve ended up with this - which I thought was right?

But when I try to adjust it correctly using PS align as a guide I think the 6 o’clock should be at about 270 degrees but it isn’t it’s miles off (used gmt but bst makes no difference - used a meridian of zero degrees)Anyone got any ideas??

[Davey-T]

There's some videos on the Astronomy Shed site about it.

Dave

[Davey-T]

No it was Astronomy and Nature site I was thinking of

Basically it says don't bother 

Dave

https://www.youtube.com/watch?v=geQszAVWMok

 

[Davey-T]

Here's another one

Dave

https://www.youtube.com/watch?v=wh5kipL1mPA

 

[8472]

You look to have the mount in roughly the right position, in your first picture (assuming you are in the uk). Simply match the current position of Polaris to whatever is produced by the SAM Console app (made specifically for the Star Adventurer range of mounts) without disturbing the R.A. axis.

Nothing more to it, and as said, forget the owner's manual, as it only adds confusion.

[Mr niall]

yes well its certainly added confusion! Have figured out where I went wrong now thanks everyone. Now I know how to do it I can file it under "things I know but will never use" and go back to using the PS Align app

[Mr niall]

Success!!

PS align shows Polaris at about 100 degrees ish - and my polar scope reticule 6 o clock now corresponds perfectly (and I aligned on the SA first to make sure I couldn’t cheat!)

quite impressed. 

 

[JamesF]

Aha!  I thought as much, but had to find my copy of the manual to read and check first.

What they're referring to is the time meridian adjustment.  It's used to adjust the scales to account for the difference between your position and the reference meridian for your timezone (because it makes a difference).  For example, I'm three degrees west of 0 degrees which is the meridian for our timezone here in the UK.  That actually means I'm about twelve minutes behind in terms of the rotation of the Earth, so if I and someone in Greenwich make an observation at the same time in our timezone, we won't see the same thing.  For example, solar noon (when the Sun is highest in the sky) occurs twelve minutes later here than in Greenwich.

Three degrees is nothing really -- probably not even noticeable within the manufacturing and alignment tolerances for the mount, but if you were in Iceland or west Africa you might actually be perhaps 20 degrees west of the meridian and you'd be about eighty minutes behind.

In this photo, the innermost scale (labelled E 20 10 0 10 20 W) is there to account for this variation:

The date ring needs to be rotated so that the correct offset for your position relative to your timezone's meridian is aligned with the white index line on the ring alongside it (and that ring must be adjusted so that the index mark is correctly aligned).

James

[Mr niall]

Yeah that’s where I went wrong, I adjusted the indicator to the zero on the time graduation circle not the time meridian circle, but one of @Davey-T videos explained it - know I’ve figured it out and recalibrated it  the whole thing actually works pretty well - in fact so well I might actually road test it on the alleged green squares due tomorrow night!

[JamesF]

Returning to this after a bit of time spent doing other things...

I still had to check that the index ring on the polar scope was in the correct position.  Years ago someone posted on SGL that Polaris transits the northern celestial pole at midnight on 1st November every year (at the prime merdian).  So if you align the index ring with a zero offset on the inner scale on the date ring, then rotate the RA axis so the rings have 1st November aligned with midnight then the polar scope should have midnight and 6 o'clock in a vertical line.

I've never questioned this initial piece of information, so I thought I should just confirm it this time around.  It doesn't seem to match the results from Stellarium.  Here is the position of Polaris at midnight on 1st November this year:

At transit it should be on the orange 0 degrees line.  Clicking on Polaris or using "Find" to locate it gives a lot of information in the top left of the screen including the "hour angle", which should be 00h00m00.0s at transit.  In fact it's 15 minutes out.  Quite possibly that's within the margin of error of the mount design, but I thought I might as well get it right, so advancing a few days I found that midnight on 5th November is very close:

And again checking the hour angle it's 17 seconds out which I think I can live with

So back at the mount I set the index ring to zero offset, rotated the RA axis so the rings read midnight on November 5th and looked through the polar scope expecting 12 to be at the top and 6 vertically underneath it.

No such luck.  I reckon it's between ten and fifteen degrees out.  Probably closer to fifteen.  Adjustment is required.  More on that when I find a suitable vertical that I can line the numbers up with.

James

[JamesF]

Ok, I found a doorway far enough away to get focus on, so I levelled up the mount (obviously necessary when you want to check something is vertical) and lined the reticle up with the edge of the doorway by rotating the RA axis:

I then rotated the date ring to read midnight on 5th November, release the grub screw that locks the index ring and aligned it with 0 on the meridian offset scale and locked it all back up again.  Sadly my photos of the scales are rubbish thanks to reflections from the flash.  I might try to take some in daylight tomorrow.

I think that's probably the best I can do for aligning the polar scope.

James

[Mr niall]

Are you going to fire it up in the field? I must admit after going to all that’s trouble I have actually bothered once and just use PS align after all. 

[JamesF]

Oh yes.  I hope we're not too far from a field test now.  I just wanted to make sure it was set up correctly first.  Obviously getting the position of Polaris on the reticle clock face from PS align or another app still requires that the reticle is aligned correctly relative to the rest of the mount and therefore to the sky in order that the RA axis will be aligned with the NCP when Polaris is in the right position.

James