Polar Alignment....Again!

[Digz]

Sorry guys but Im hoping someone can explain this to me in laymen's terms (very laymen's terms!!!)

I have adjusted the reticule on my EQ6 so it aligns with the polar axis of my mount - that was no problem. In actual fact it was pretty much spot on from the outset.

I have since followed both the EQ6 user manual and Astrobabys help page on how to orient the polar scope and this is where the confusion lies.

I understand about setting polaris in transit and have done that several times setting the date and adjusting the marker to suit and adjusting and setting the RA setting circle.

However if I follow the manual and work through on how to polar align the scope it seems to undo the effort just made above. That is the RA setting circles are re-adjusted for the time of observation and the date / lon scales are also adjusted.

Am I missing something really simple here? I hope someone can shed some light on this so I can get to grips with aligning my mount ready for when the clear skies return.

TIA

[roundycat]

I believe you can polar align approximately with the pa scope and then drift for ten minutes or so and get it as close as you are ever going to need. worrying too much about the precise details of pa with a scope or setting circles or anything else is, in my view, counter-productive.

Drift alignment takes minutes to learn and it will serve you forever.

Dennis

[Digz]

Thanks for the input but that just seems even harder to get to grips with than polar alignment?!

[RayGil]

I found this today:

Polar Alignment of your Equatorial Mount - McWiki

and

Finding and Tracking Objects with an EQ Mount - McWiki

This explained a lot to me.

Hope it helps.

RayGil

[Astro_Baby]

The RA circle arent moved in alignment as such - in fact the RA scale stays locked at its zero position,

If you look at my guide then this page covers setting up the polarscope

Astro Babys HEQ5 for Idiots Page

During that process you set the scales by rotating the date scale to align with the RA scale at a time for polaris transit.

The next page Astro Babys HEQ5 for Idiots Page covers setting up the scope for observing. The RA scale stays locked but as you rotate the RA axxis (NOT THE SCALE) the polarscope date scale moves around. When the RA axis is rotated you watch the date scale on the polarscope. When the time and date you are observing are matched then the polarscope reticule is in the right position.

Read through the guide and dont jump ahead - the guide was written to be accurte so long as you follow it absolutely exactly. Reason being polar alignment using the scales is somewhat counter intuitive.

Hope that helps.

[Digz]

Hi RayGil, thanks for the links, Ill be sure to peruse them shortly.

Hey Astrobaby, thanks for the input. Ive been using your guide and most of it is making sense. However I have an EQ6 mount and here is where the confusion arises. On this mount the time scale is up by the RA and therefore away from the date scales on the reticule. This makes it hard to align, for example, when setting polaris in transit. I think further confusion arises as the manual says to loosen and rotate the RA scale when polar aligning, which as you say, shouldnt be done once the reticule and polaris transit has been set!!!

Im hoping it will stay relatively clear tonight so I can try and align and see what happens!

[themos]

I find that I just look at the angle the Plough makes in the sky and match that with the reticule diagram of the Plough (by rotating the RA axis).

[Digz]

hey themos, do you know, that did cross my mind and I wondered if that was a simple solution?

[themos]

It's good enough for visual and, if you're guiding, for imaging at a short focal length. For unguided imaging or for long focal length imaging, I do a bit of drift alignment afterwards.

[Digz]

thanks for the input themos.

[Astro_Baby]

There are simplere solution - if your EQ6 is GoTo when you do the align the handset will give you two Polaris times. One is the hour angle and the other is the clock position.

Hour angle is simple - when the handset says POlaris HA is (for example) 10:00 then it has been 10 hours since Polaris transited sooooo

1) look through the polarscope and turn the mount through its RA axis unti polaris is at the bottom.

2/Lock the RA axis

3/Set the RA index scale to 0 and UNLOck it.

4/Release the RA scale lock.

5/Rotate the mount through the RA until 10:00 on the RA index scale is at the index mark.

6/Lock the RA axis.

You are now ready to align polaris.

You are 10 hours around the scale from when Polaris last transited which is correct.

Even simpler method is the closck position. When you do the Syanscan align the handset will tell you after you input date and time and lat/lon where Polaris is - ie it will say POlaris CLock Position 07:30

Look in the polarscope and rotate the mount through is RA axis until the polaris marker is at the 7:30 position (on an imaginary clock face).

There ya go - two other methods. The Hour angle method is accurate depoending on the RA scale - on my mount the RA scale is always a bit sticky so I use the methid in my guide BUT if I am pushed I do use the cloack position method which is plent accurate enough for observing with.

Hope that helps

[Digz]

Hey Astrobaby, many thanks for the alternative methods. Ill be sure to give them ago, they sound a lot easier. Just one question though, do I need to ensure I have my EQ6 adjusted first for a polaris transit? I only ask as the RA scale can be moved and presumably this needs to be set in the right position first?

Sorry for all these questions but this is a big learning curve for me. Ill be glad to get the scope outside and try these alignments but the damn cloud has set in again.

[Astro_Baby]

I'm not reallu sure what your asking but I'll try and answer in a general way and hope the answer to your question is in there somewhere. I hope none of this sounds patronising.

Basic Principals

The object of the polar scope and its associated setting circles is its a kind of three element slide rule. In essence by knowing two of the following;

date

time

polar position

the third can be calculated. SO if you know the time and date you know where polaris is - alternatley if you know where polaris is and the date you can work out the time and so on.

We are really only interested in knwoing where Polaris is as we have watches and calendars

Now before the polarscope and its setting circles can work we need to set them to a known position and zero them.

IN a nutshell what happens is this

YOu rotate the RA axis until POlaris is at the transit position (the bottom) at the 6 o clock position if it were a clock face. This is in effect zeroing the first part of the slide rule (ie the polarscope is set to the polaris transit posn)

With the POlaris market at the 6 o clock position lock the mount in RA and lock the RA setting circle as well. Its not used except in its locked position with zero opposite the index mark.

That sets the 2nd part of the slide rule.

Recap - we now have Polaris at its transit point (firts part of the slide rule now zeroed)

We also have the time circle (the RA index scale) locked to its zero position. That just leaves us to set the third circle.

Now if we know that Polaris will transit on the 10th of January at 22:00 we need to set the circles. So what happens is we set the date circle (the one on the polarscope) so that its date of the 10th of January is level with the RAs time of 22:00. Do this by turning the circle itself NOT the polarscope or the RA axis - just gently push the circle round till its aligned.

So now we have POlaris at the base at the 6 o clockn position

The RA scale locked at zero

The Date circle now lined up so that 10th Jan is opposite 22:00 on the RA scale.

You see now that the circles are set corrrectly - POlaris was to transit on 10/Jan at 22:00 and thats exactly how the mount is set up. ie 22:00 is level with the 10th of Jan and Polaris DOES show as in its transit point.

Thats all we have to do BUT what happens when you want to use the mount on another date or time.

Thats where you zero the date scale. Now currently your date scale is set at 22:00 opposite the 10/jan yes ? of cousre it is cos you just set it but the date circle also contains an inner scale for longitude offset (we dont use that) which convenienetly has a zero in the middle of the scale. So you mark where that zero lies using the date scale index marker (the small circle with a white notch on it) - you point that at zero on the date scale'lom offest scale and lock it down. The sole purpose of this is so you know where the date scale should be in case it gets moved (they are usually quite loose).

So now you know the three zero positions - the Poarlscope zero is with the polaris marker at 6 o clock at the bottom. The RA scale is locked to its zero position all the time and the date scales zero position has now been set and locked in synch with the other two circles (polaris marker and the RA) so you can put the date scale to a known zero position at any time.

So now you have all three zeros registered and the polarscope can now be used to align the mount because if you know the date and time the Polarscope reticule will show where Polaris is. Heres how.

OK you have set/calibrated the scope using the instructions above but now you want to observe and its now the 25th of March and the time is 23:00

This is the clever bit - I said the polarscope can calculate any one thing if it knows two of the factors -

Remember this;

Date

Time

POlaris Position

Well you know the date - its the 25th March

You know the time - its 23:00

So you make sure that the RA index marker is locked to zero and the polarscope date circle has its zero (the one on the longitude offset) set againts its white marker which is a known quantity (ie when you set it the scale was lcoked to a known position of Polaris and as a result the three scales (polaris reticule marker, RA scale and the date scale around the polarscope are all in synch).

So you release the RA lock and rotate the scope in RA until 25th of March on the date scale lines up with 23:00 on the RA scale.

Wherever POlaris shows in the polarscope is where Polaris is at that moment.

Shimple eh ?

When yu set the mount up you in effect locked all three elemnst to a common point (polaris transit) so now you can always find Polaris position by aligning the date on the date circle with the time on the RA scale by rotating the mount in its RA axis . Thats all there is to it.

Once the scales are set for a known transit all youhave to do is rotate the mounts RA axis until the correct date and time for your observing session is aligned and look theorugh the polarscope.

How often so you need to set the polarscope ? I seldom bother resetting mine. Its accurate enough for a while. I tend to reset it IF I have time and energy ahead of observing and as close as possible but its not really neeeded. Once set its should last quite a while.

I hope that all makes sense and helps somewhat.

[Digz]

Astrobaby, that is perfect, just what I needed......

Ok maybe I spoke too soon. I get everything above and have everything set up, Polaris is in transit and 10th Jan lines up with 22:00 and 0 on the RA setting circle is against the marker, heres where Im struggling:

"So you release the RA lock and rotate the scope in RA until 25th of March on the date scale lines up with 23:00 on the RA scale."

The RA setting circle is lined up so that 22:00 matches 10th Jan and they are synced together, therefore when I rotate the RA 23:00 will not match with 25th March unless I move either the date circle or RA setting circle - is this right? If so which one do I move?

wow, i didnt think this could get so complicated so quickly.

[Astro_Baby]

Nope -

The RA setting circle is lined up so that 22:00 matches 10th Jan and they are synced together, therefore when I rotate the RA 23:00 will not match with 25th March unless I move either the date circle or RA setting circle - is this right? If so which one do I move?

Nope - when you rotate the RA axis - so long as the RA circle is locked - the date disk around the polar scope will move around the RA circle.

Test this - LOACK the rA index scale at 0. Now put the zero on the date scale in line with the zeor on the index marker.

Rotate the mount around its RA axis and you will see the zero on the date scale is moving around the RA scale.

[Astro_Baby]

Where are you by the way - I dont think I can explain this anymmore than that via text but if your anywhere near Gatwick I could show you on a real mount.

[Digz]

This is true, the date scale will rotate when I move the RA around but Im also finding the RA setting circle is also rotating around i.e. with the movement of the RA, it sounds as though this setting circle should not move anymore once set so maybe I haven't locked it tight enough. Unfortunately I am not near gatwick, but I really appreciate the offer. Ill try tightening the RA setting circle some more an see if that works.

[Astro_Baby]

If the EQ6 is like the HEQ5 (I cant recall) the circle will only lock at the zero point - ie when 0 is under the index mark it will lock. In all other positios it wont lock reliably.

There is a small hole drilled in the back of the index scale for the RA which the lock knob locks into as far as I recall.

I think thats the problems. With the RA scale locked the RA axis will rotate along with the polarscope and the polarscope date scale - the RA scale wont budge. Or at least it shouldnt.

[Digz]

Thats what I was thinking. That way, once everything is set up as above I can then turn the RA axis, with the setting circles remaining still, so that the correct observational date lines up with the correct time. I might see if I have some pliers to lock the RA setting circle some more, the annoying thing is the second locking screw on the RA setting circle, once polaris transit is set is in such a position that it cannot be easily tightened!