Thread: Polar Alignment
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Old 07-03-2020, 09:57 AM
Startrek (Martin)
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Join Date: Dec 2017
Location: Sydney
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Peter,
Following on from Carltons great information here’s 2 procedures I wrote , firstly how to find True South (very accurate ) and secondly how to polar align the HEQ5 mount using the Synscan hand controller ( I’ve been using the PA procedure for nearly 4 years now and usually only takes me 10 minutes)

Finding Celestial True South using Solar Noon Meridian method

Items needed
1 metre length of 12mm diameter timber dowel with a 2mm deep 90 deg cross cut into one end using a hacksaw
2 x 3 metre pieces of 1mm string cotton type
4 x weights like a brick or paver etc...
1 x straight edge, alum angle or ruler 500mm long would be good
1 x fine point black permanent marker
1 x 300mm long Stanley or quality boat type builders bubble level
1 x PC with a planetarium software program. Stellarium is a good choice as it’s free and easy to use
1 x Smartphone like an iPhone

Location
Your observing location ( approximately 1.5 sqm ) or where you will set up your telescope mount should be a reasonably flat and level area with a good view of the sun at around midday ( a paved , tiled or concrete area is preferable) At a remote site you will need to clear the ground and make it reasonably flat or level

Procedure

(Setting up for your Shadow)
Erect timber dowel vertically below your preferred observing tripod position and use the 2 strings to anchors the dowel like tent guy ropes at N,S,E and W using weights to hold it in position. Use your bubble level to ensure dowel is exactly vertical at 90 deg in all directions ( very important ) The hacksaw cuts at the top of the dowel make it easy to adjust the dowel N,S,E or W

Finding Solar Noon Time

(Using your Planetarium like Stellarium )
Start your PC mid morning and open Stellarium. Rotate your cardinal point to the North position and raise view up until you see the Sun
Click on the Sun and then click on the clock , move the time forward or backward to the point where the Suns Alt/Az degrees goes from 359 deg to 0 deg or exactly bisecting the North South meridian line ( refer to top left hand data on screen for Az/ Alt deg )
Record this exact time which is Solar Noon ( hypothetical eg 12.35pm )

(Finding Solar Noon on a Website)
Most meteorological websites show Solar Noon times at or near your observing location

Marking your Celestial True South Line

Go to your observing location 10 minutes before Solar noon with your smartphone , ruler and permanent marker. The dowel should be casting a 12mm wide +500mm long shadow on the surface towards the south
At exactly Solar Noon time mark a thin line on the surface or ground from the central base of the dowel outwards along the exact centre of the shadow for at least 500mm ( be as precise as you can )

This line is marks the Celestial Meridian (True North / South )

Use this line to align your tripod front leg “N”to True South and then set up your mount
I found this method far more accurate than any app or compass with magnetic declination


Synscan Polar Alignment Routine V4 Skywatcher EQ Mounts ( used when no view of SCP )

1/ You will be using a 2 Star Alignment to start the process so nominate your 2 Alignment Stars on the same side of the meridian, one of which will be your Polar Alignment Star ( Alignment Stars should be fairly bright stars where possible to ensure they appear in the Synscan hand controllers data base, usually greater than magnitude 2.5 )
(Alignment stars for polar alignment ideally should be located between 35 degrees and 70 degrees in Altitude and no more than 50 degrees in Azimuth from the meridian) Important - Your Polar Alignment Star or 1st Star Alignment Star will be the one closest to the south meridian. To assist with locating and nominating your Alignment Stars use a Star Chart, a Planetarium like Stellarium or Cartes Du Ciel.
2/ Complete a 2 Star Alignment generally in accordance with Syncan 2 Star Alignment procedure. Start with your 1st Alignment Star close to the south meridian ( this will be your Polar Alignment Star as well ) and then 2nd Alignment Star away from south meridian no further than 50 degrees in Azimuth
3/ After completing a 2 Star Alignment press “Menu” then “Alignment” then “Polar Alignment” and then “Enter”
4/ The screen will display “ Select Star”. Scroll through list of stars until you find your previous nominated Polar Alignment Star and press “Enter”
5/ Mount will slew to the selected Polar Alignment Star
6/ Use direction keys on the hand controller to centre the Polar Alignment Star in the telescope eye piece reticle or Computer screen reticle. Once centred press “Enter”
7/ The hand controller screen will now display the polar alignment error ( degrees: minutes: seconds) then press “Enter” to proceed
8/ The mount will now slew to the new Altitude position. Now use the Altitude adjustment bolts only to move the Star to the closest point to the centre of FOV on the reticle eye piece or computer screen reticle. Remember this position and then press “Enter” to show the new polar alignment error ( degrees: minutes: seconds )
9/ Press “Enter” again and mount will slew to the new Azimuth position. Now use the Azimuth bolts only to move the Star to the closest point where the Star was centred in step 8. Press “Enter” to show the new polar alignment error
10/ Press “Enter” again to end the Polar Alignment procedure
11/ Go back to the “Alignment” menu in the hand controller and execute another “2 Star Alignment”. 1st Alignment Star will be your Polar Alignment Star which you should be already centred on from the previous Polar Alignment routine and 2nd Alignment Star is further away from the south meridian.Once the 2 Star Alignment is completed , the polar alignment error will be displayed on the hand controller ( degrees: minutes : seconds )
12/ Repeat the above procedures ( iterations) 2 or more times as required to reduce your polar alignment error below 1 arc second in both Altitude and Azimuth.
Polar Alignment Error displayed on hand controller should show as many zeros as possible
Eg: 1 arc minute error 000 01’ 00” Eg: 20 arc sec error 000 00’ 20”
Try and get below 1 arc minute error in both Altitude and Azimuth if conditions and time permit.
13/ Note: you must perform a 2 Star Alignment before you start with a Polar Alignment routine each time
14/ To improve accuracy of your Star centering and alignments , de focus the star slightly into a small donut shape, this way you can perform more accurate centering operations looking into your reticle eye piece or at your computer screen reticle
15/ The 2 Star Alignment stars you use for Polar Alignment maybe different from 2 Star Alignment stars you use for locating objects ( Goto) as the accuracy of Goto may improve with a wider distance between alignment stars in Azimuth.The 2 Star Alignment stars for Polar Alignment are fairly close to each other near the meridian and only span a small part of the night sky. The Polar Alignment routine obtains better results ( lower error ) when Alignment stars are within 50 degrees apart in Azimuth and closer to the south meridian at between 35 degrees and 70 degrees in Altitude.
16/ With some experience the Synscan Polar Alignment routine can usually be completed with sub arc minute PA error in around 15 to 20 minutes depending on seeing conditions
17/ Note: Star Alignment and Polar Alignment are two different processes
Star Alignment is used to tell the mount exactly its location in the night sky on an object using singular or multiple pointing model algorithms.
Polar Alignment is aligning the central axis of the mount and telescope to the South Celestial Pole using the Altitude and Azimuth adjustments. Depending on the accuracy of Polar Alignment,the celestial object will remain stationary in the FOV for at least a minute or so before any noticeable drift.
However Polar Alignment and Star Alignment do affect each other when adjustments are made. An adjustment of Altitude or Azimuth affects your star alignment accuracy, that’s why you perform a 2 Star Alignment after PA is adjusted.

Hope the above helps in some way

Cheers
Martin
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