Here are two methods to precisely find the polar axis of rotation of the Earth:
- With the help of software and a CCD camera
- The star hopping method
1- With the help of software and a CCD camera
For an investment of approximately $400 Canadian, it is possible to align the mount with the North Celestial Pole (NCP) or the polar axis of rotation of the Earth with an accuracy of up to 30 arc seconds (30″ arc). It requires the use of a German equatorial mount. The software is used Pole Master with the CCD camera dedicated to it. This precision will allow exposure times of 10 minutes or more per photo. Usually, polar alignment can be achieved in just 2-3 minutes after starting the software. This is the revolutionary method to align the mount on the axis of rotation of the Earth in record time!
Click on this lien to consult the user guide.
2- The star hopping method
The star hopping method for finding the North Celestial Pole (NCP) requires no monetary investment. It is valid for both German equatorial mounts and azimuthal mounts equipped with a equatorial table.
This method uses the same approach as the software Pole Master above. It also uses guide stars near the PNC to locate it. However, it requires more dexterity from the user since there is no software assistance to find the PNC.
Considering that stars rotate around the Earth's rotational axis (PNC) every 24 hours, I recommend using your tablet or cell phone and turning off the screen rotation function (1). With these devices, you only need to display this web page. Thus, when searching for guide stars, you will need to rotate the images shown below (rotate your tablet or cell phone) to match the current view. This will greatly improve the search for stars near the PNC. Thus, instead of software assistance to find the PNC, you will have visual assistance from your tablet or cell phone to locate it.
As you can see, visually the Earth's polar axis of rotation or PNC points towards the dipper of the Little Dipper. From Polaris, you can draw a straight line to the star at the tip of the dipper of the Little Dipper (see the red line). Move the telescope's finderscope in this direction (using the azimuth and latitude knobs on the mount), right next to Polaris.
Using the telescope finder, search for the 3 guide stars connected by the red triangle above.
- The image seen above is as seen in the finder (North-South and East-West inverted image). Rotate the image to match the current view.
- Be careful with the image to the researcher being inverted, the Cabin Crew Member appears opposite the star of the Little Dipper.
- Starting from the bright star near the North Star, connect the three bright stars from 1er triangle in blue. This first location will help to find the 3 guide stars of the red triangle.
- Look for the 3 bright guide stars that are connected by the red triangle in the image above.
- Still using the mount's azimuth and latitude buttons, position the finder's reticle (the X) towards the North Celestial Pole as shown in the image above.
- Put on an eyepiece or install your CCD camera offering a field of view of at least 35 ′ of arc. To know the field of view of your eyepiece or CCD camera (or other digital cameras), click on this lien. The image shown above is with a 40mm eyepiece.
- The image seen above is as seen through the eyepiece through the Edge HD 800 telescope through the elbow (East-West inverted image).
- Rotate the image to match the current view. Find the 3 bright stars near the North Star (see red). Note: Be careful, the Pole Star revolves around the PNC in 24 hours so that its position varies continuously.
- Inside the triangle formed by the 3 stars, find the star that is twice the distance from the rotation axis. Center the rotation axis (the imaginary red dot) in the center of the 40mm eyepiece view. This initial positioning will allow you to point precisely at the polar rotation axis in the next step below.
The polar axis of rotation for the years 2025 and 2026
Due to the movement of precession of the equinoxes, the Earth's rotational axis (or North Celestial Pole) is slowly moving over time at a rate of 50,29″ of arc per year. Currently, this movement is bringing it closer to the North Star. Here is its position for the years 2025 and 2026:
The image seen above is as seen through the 40mm eyepiece through the Edge HD 800 telescope through the elbow (East-West inverted image). Rotate the image to match the current view.
Using the mount azimuth and latitude buttons, move the mount in that direction. For more precision, you can use a illuminated reticulated eyepiece. Center the reticle on the imaginary red line of the red triangle, just below the three reference stars in the blue circle above.
You will thus obtain an alignment precision very close to 1′ of arc of the PNC and even a little less depending on your skill, which will allow you to achieve exposure times of up to 10 minutes per photo and even a little more with parallel autoguiding.
If you are using a CCD camera to center the PNC, you can display a reticle in your favorite imaging software as in the following example:
With the CCD camera, use the following image as a reference:
The reference image seen above is as seen with a CCD camera through the Edge HD 800 telescope (without elbow). The image is reversed East-West and North-South. Rotate the image to match the current view. Please note that the field of vision varies depending on your equipment.
(1) Screen rotation
If necessary, to prevent screen rotation on your tablet or cell phone, from the top right of the screen, move your finger down, press the following icon which is circled in red:
Some older devices require you to swipe up from the bottom of the screen. If these two methods don't work on your device, do a Google search:
How to enable and disable automatic screen rotation on my « Tablet or cell phone model name”.
If you do not have an internet network at your observation site, use your cell phone's mobile data (Settings | Connections | Data usage | Mobile data).
To use your tablet, enable a Mobile Hotspot on your cell phone (Settings | Connections | Mobile Hotspot & Tethering | Mobile Hotspot). Then, on your tablet, connect to your cell phone's mobile Internet network.
If this is too complicated for you, print the images presented above and bring them to your observing site. On your personal computer or other device, right-click (with your finger on the image) and select Copy Image. Simply paste the image into your favorite word processor and then print it. Repeat this process for each image you want to bring to your observing site. To protect printed images from moisture, place them in a clear plastic envelope.
If you don't have a printer, ask a friend who does to print them for you.
Richard Beauregard
Sky Astro - CCD
Revised 2025/08/27