Polaris Transit - Equatorial Mount

[nheather]

Question ...

If I were to polar align an equatorial amount at the date and time of the transit of polaris whilst on the central meridian of my local time zone what would the mount look like.

In paricular how much would RA be rotated?

Will it be dead central with the weight arm pointing directly down?

Or could be at any position depending on location, and the particular transit?

Cheers,

Nigel

[nheather]

What I'm trying to say, is would it look like this?

Or could it look like this?

Or any other RA orientation?

Cheers,

Nigel

[nheather]

That first picture is meant to be vertical - it is in the original and in photbucket but it has been rotated by 90 degrees for some reason in the forum post.

Cheers,

Nigel

[themos]

Since you will presumably be using the polarscope (I can see a cover that seems to hide it), the thing that matters is the orientation (and precise centering) of the reticle in the polarscope, and that is independent of the movement you show. 

[nheather]

I'm actually trying to fit and set up a polarscope and totally confused by it.  That is why I am asking this question.

Cheers,

Nigel

[Tinker1947]

The polar scope has to be central in its housing, you would get it centred on a distant object then turn the polar scope so the centre of the polar scope stay steady on the object, there are adjusters to help with this.....Then you do the mount aligning....

[themos]

I can sympathise, I never use the date and time circles for the polarscope as I've never figured out the process. I either eyeball the constellations on the reticle to kind of match with what I see in naked-eye sky, or else use EQMOD to rotate the axis the right amount.

[Tinker1947]

This is some software that tell where Polaris position should be at any given time, so you just adjust the RA and DEC until Polaris is in the little bubble, this is after you have aligned the polar scope.....

The software

http://myastroimages.com/Polar_FinderScope_by_Jason_Dale/

[nheather]

The polar scope has to be central in its housing, you would get it centred on a distant object then turn the polar scope so the centre of the polar scope stay steady on the object, there are adjusters to help with this.....Then you do the mount aligning....

Yes I understand that bit - haven't got that far yet.

The thing that has got me stumped is that the reticule rotates with the RA.  I have 5 thin shim washers that came off the telescope and I presume you are mean to use some of those to set the polarscope to the best position.  The bit that is doing my head in is this - let's say polaris is in transit so directly above the NCP.  Looking through the polarscope, polaris will appear below the NCP because the image is inverted.  Now depending on whether I fit 0,2,3,4,5 or 6 shim washes I can make the polaris appear below the NCP for 6 different RA settings.  They can't all be correct, can they?

Cheers,

Nigel

[Tinker1947]

i dunno those RA setting done my head in so i just set it to the circle and the bubble..with the constellation close to what they were in the sky...

[nheather]

This is some software that tell where Polaris position should be at any given time, so you just adjust the RA and DEC until Polaris is in the little bubble, this is after you have aligned the polar scope.....

The software

http://myastroimages.com/Polar_FinderScope_by_Jason_Dale/

See this diagram

The reticule rotates with RA, and I have 5 shim washers but no idea how many should be used.  As a result for any given RA I can have 6 different reticule orientations.  They can't all be right.  At a given time if I line each of these reticules up on polaris I will end up with 6 different polar alignments won't I? 

Cheers,

Nigel

[Tinker1947]

These shim washers are something new to me, i don't understand where they would go........

[LouisJB]

I'm no expert but I got my HEQ5 pro working nicely, the process is approximately;

Ensure the recticle is centred. that is key as a one-off activity you can do in daylight in advance of anything else.

This is the polarscope setup process (again you can do this in daylight)

Find any transit date and time (in your time zone or UTC if you prefer, whatever you decide will be the definition of time you'll use later). Transit time = time directly above true NCP, which is directly below in the polarscope. A near transit might make sense, but really any will be ok. There's mobile apps etc to help. Most manuals suggest a date and time.

Lock the Dec clutch (in the position where you can see through the polar scope.

Now, rotate the RA axis until the polaris circle is directly down, i.e. where it will be for transit (as it is inverted). Lock the RA clutch. The angle of the RA will be arbitrary, don't worry about it.

Set your date circle and time circles to match the selected transit time (in the timezone you want to use as above).

Now when that's done, carefully move the line on polarscope to the 0 line on the date circle.

That's it in terms of setup. I did mine once, has been good since (unless you change location...)

Now, when you're in position to polar align at night. Just set the time circle for your current time (in the selected timezone) to the date circle for the date of observation by moving the RA around. This will rotate the polar scope to the right position. Lock the clutch.

Now align polaris in the middle of the polaris circle using alt and az adjustments only.

Job done.

[themos]

 presume you are mean to use some of those to set the polarscope to the best position

I really doubt that. 

You can end up with any orientation of the reticule you like (as long as it's aligned with the mechanical axis of the mount so that the + does not wander off a star when you rotate the reticule in RA). 

So, as you say Polaris is high, so will appear low in the polarscope. Fine. Here's what I do: Use Alt and Az adjustments to bring + over Polaris. Now we know we are pointing just below Polaris-in-the-sky so we need to raise the polar axis a bit. Use just the Alt adjustment to bring Polaris on the big circle but below the +. The polar axis goes up, Polaris comes down. That's it. You can now loosen clutches and rotate in RA until the o is on Polaris. The o will now track Polaris as soon as you turn the RA motor on. 

Another night and a different time, we know Polaris is not exactly at transit but somewhere in between. What do we do? 

a) Put Polaris at +  using Alt/Az. 

Using Alt only "raise" Polaris to the circle above the +.

c) Loosen clutches and rotate RA axis until reticule shows o over Polaris.

d) That's the 12 o'clock home position of EQMOD (Polaris at its lowest point in the sky)

e) use some astro calculator to tell you what angle away from that position Polaris is at that time and what direction. 

f) loosen clutch and swing RA axis by that amount 

g) look where the o has ended up and use Alt/Az to put Polaris there. 

e) is done with a mount control program like EQMOD or by software like PolarFinder (or by the polarscope dials if you're hardcore).

h) sanity check with the constellations. if you look at the sky, do they look like they do in reticule?

[LouisJB]

I should add, when rotating the polarscope marker to 0 date on the date circle, there's a small grub screw to release and re-tighten. You do this without moving the polarscope or RA angles.

Later when you are setting up for alignment, make sure the polarscope is again at 0 on the date circle and then rotate the RA to get the date and time to align on the circles. The Date circle can move freely so checking the polarscope is at 0 is something I do before setting the date and time for alignment - otherwise you'll get incorrect alignment.

The first time you go out you can check you got it right, the stars in the polarscope should look exactly like they do in the sky.

You can actually check this any time of day using something like Stellarium at some arbitrary time and setting your polarscope date and time to match, the views should agree, allowing for inversion - that's actually how I checked mine before going out with it for the first time. So long as you set Stellarium to your location and use a constant definition of time then any point in time they should agree on where the stars are.

[JamesF]

As I seem to have posted a fair bit recently, the rotational position of the RA axis when the reticle is aligned such that Polaris appears in the indicator is irrelevant.  The time and date rings on the RA axis need to be set so they align correctly with the position of Polaris, but the orientation of the counterweight bar etc. just doesn't matter.

Assuming the polar scope is correctly aligned, you'd take out the mount, point it north-south, unlock the RA clutch and turn the RA axis through whatever angle is necessary to set the time and date on the RA rings and lock it off again.  Then you look through the polar scope and align Polaris with the Polaris indicator.  That done, the mount is polar aligned.  You can release the clutch and rotate the counterweight bar back to point downwards.  The mount is still polar aligned.

The position of the counterweight bar when the mount is correctly aligned and Polaris is in the Polaris indicator will change as the time of day changes and the date changes.  It must do this, because Polaris appears to rotate about the pole once every 23 hours 56 minutes.

James

[JamesF]

To answer your question specifically however.  At the transit of Polaris regardless of your position the mount will be in the same position every day, and that will be whatever position rotates the polar scope to put the Polaris indicator vertically below the NCP cross in the reticle.  The amount of rotation of the RA axis could be anything at all depending on how tightly the polar scope unit is screwed in, but at the time of transit of Polaris the Polaris indicator will always be at the bottom.

(Transit is when Polaris is "above" the NCP, but because the polar scope inverts the image, the Polaris indicator is lowest at that point.)

James

[LouisJB]

Assuming the polar scope is correctly aligned, you'd take out the mount, point it north-south, unlock the RA clutch and turn the RA axis through whatever angle is necessary to set the time and date on the RA rings and lock it off again.  Then you look through the polar scope and align Polaris with the Polaris indicator.

That's exactly what I've been doing and it seems to work really well. The only thing I wonder is about timezone change - i.e. in the UK what will happen now we just lost an hour coming out of BST, will the times on the setting circle be out by an hour, assume they must be. So I can either remember that and allow for it or move the polarscope alignment around by an hour.

What do most people do in this situation, seems odd to have to make adjustments twice a year for this, maybe easier to just use UTC always?

[JamesF]

The setting circle times are GMT/UTC.  During the summer you need to subtract an hour to get the correct time for the setting circles.

James

[LouisJB]

Right ok, I think I worked out a local transit time during the summer, my pc would have used BST and so my initial calibration is now out the other way.

So now we've left BST I need to add an hour!

No worries, I suppose either works so long as you remember. I'll probably shift it around by one hour at some stage to avoid confusion in the future and stick with the UTC thing, sounds easiest to follow that convention.

[richardalan]

Hi Nigel, I found this link quite helpful: http://www.astro-baby.com/HEQ5/HEQ5-1.htm I recently got one of these mounts, and I found the Polar alignment section in the instruction manual totally confusing, but this definately made it a lot easier for me to understand!

Rick.