Polar Alignment Overview
Polar Alignment is the physical alignment of the Equatorial Axis of an Equatorial Mount, to the Celestial Pole, which is a point in the sky that stars appear to rotate around.
See EQ Mount pointing to the SCP (pictured by Star Trails).
Aligning the axis of an Equatorial Mount to the Celestial Pole in necessary to prevent field rotation distortion around the edges of an Astro Image if the camera sensor does not turn at the same rate as the earth.
A YouTube video animation “Polar Alignment Demystified” on Polar Alignment concepts.
The two parts to adjusting the Polar Alignment:
1. Course Adjustment
- Course adjusting the tripod to point to the True South (or North) Pole while keeping the mount level.
- Course adjusting the mount altitude of the mount.
2. Fine Adjustment
- Adjusting the azimuth bolts to align the mount to the True South Pole (or True North Pole)
- Adjusting the altitude bolts to set the Equatorial Axis to the same value as the latitude.
The Basics
1. Solid Footing:
Ensure the tripod has a solid footing on the ground. Small movements on the ground are greatly amplified at the mount. Particular attention to the mount not moving on soft ground or grass. The use of pads underneath the legs can help the legs not to sink or move on soft ground.
2. Pole alignment:
A compass is used to align the mount to the South (or North) Pole. The compass needs to be away from any magnetic materials in order to give an accurate reading. (including magnetic items like a wristwatch, keys in pockets etc.)
It is necessary to also allow for Magnetic Declination so South or North on the compass points to the pole while the compass needle points to the Magnet Pole.
A compass stick can be used to accurately point to the true pole.
3. Tripod Level:
Accurately level the tripod using a spirit level.
A level tripod is not a requirement of Polar Alignment. The only thing that has to be aligned with the pole is the Equatorial Axis of the mount so that the Right Ascension (RA) motors rotate the Equatorial Axis and thus, rotate the camera around the pole. The tripod can be at any angle to achieve this requirement.
A level tripod is required to facilitate later fine-tuning of polar alignment using a computer application. The application will require you make slight adjustments either to the altitude or azimuth bolts. The application relies on the mount being level as a reference to these adjustments.
Once level, recheck alignment to the pole and if necessary, keep redoing the alignment and level until both are correct.
4. Mount altitude:
Attach the mount to the tripod and adjust the altitude bolts so that the angle matches the local latitude. An inclinometer on the RA axis can assist with this adjustment.
To understand why the altitude bolts are set to the same angle as latitude, see this explanation.
You now have a rough polar alignment.
Fine Tuning with specialised software applications.
Two of the quicker & popular ways of fine-tuning the polar alignment are using a software application called Sharpcap, or a Hardware/Software combination called PoleMaster.
Sharpcap is probably the quickest and easiest but you must-have gear that meets its requirements. A guide scope that meets those requirements, aligned with the main OTA is best, it should be in focus.
The PoleMaster application requires you to pick out some key stars in the sky near the pole. Because PoleMaster comes with its own camera, you don’t have to worry about the hardware requirements for your existing guide camera.
The Sharpcap application may also work with the PoleMaster camera which both removes the need of meeting Sharpcap hardware requirements and simplifies the alignment process.
A device that seems to have a simple alignment application and its own camera
that is similar to the Polemaster is the iOptron iPolarTM Electronics Polarscope
Useful Links
Using Sharpcap:
Ensure your gear meets Sharpcap's requirements
Also, check out the Sharpcap tips
Sharpcap location settings. Set the exact latitude & longitude of your location and enter it into the screen in the Polar Alignment tab in Sharpcap menu “File->Sharpcap Settings”.
(Tick the box “Correct for Atmospheric Refraction”)
And if having issues, check out the Sharpcap troubleshooting information
Sharpcap Manual on Polar Alignment
Some YouTube videos on Sharpcap
YouTube interview of Robin Glover, the Sharpcap developer. (note the outreach comments) Polar Alignment mentioned at the 24:11 time in the video.
A text version of the above Robin Glover interview from a US Astro magazine.
QHYCCD PoleMaster
https://www.qhyccd.com/index.php?
PoleMaster (manual)
https://www.qhyccd.com/index.php?
Some YouTube videos on PoleMaster
QHY PoleMaster - Introduction and Polar Alignment Walkthrough
How to Use the QHYCCD PoleMaster Software
The Astro Imaging Channel QHY PoleMaster
Polemaster Unboxing and Fitting to a HEQ5 mount Part 1 (except that cable connector should be mounted on the right side of the camera)
PoleMaster part 2 using it and then using SharpCap as a comparison.
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