Speedy Polar Alignment

SPA –  A Tool for Polar-Scope and Web-cam

Many people are adding web-cams to their polar-scopes to make polar alignment easier (on their knees and neck!).

By using SPA as part of your set-up routine you can make polar alignment more accurate and faster too.

Speedy Polar Alignment window

Version now available…


{revision history} : Initial release Improved faster horizontal calibration process.

Unzip the zip file and run the setup program to install it. As I haven’t paid lots of money for a certificate of authentication Windows will warn you that it cannot verify the package.

How does SPA work?

There are two ways to use SPA:

  1. Just use it as a Polar Scope Hour Angle utility on your computer.
  2. Overlay SPA’s window on a polar scope webcam view and accurately set your polar hour angle.

SPA is a transparent-window app that displays the polestar hour angle. The idea is to place SPA over the top of your favourite webcam viewing app (such as SharpCap) and then follow a few simple steps that quickly get you to accurate pole-star alignment (to within 30 arcseconds)

Your polar scope reticule may not be accurately aligned to the polar axis. With 3 mouse clicks SPA helps you by calculating and showing the true axis.



  1. Level the mount and sight your pole star in the polar-scope
  2. Fit the webcam and view the image on your computer
  3. Set the Longitude of your location in SPA
  4. SPA is currently Windows only and requires .NET 4.5

1. Web-cam Horizontal alignment.

Align the web-cam view so that when you adjust the Azimuth bolts the pole-star moves across the screen approximately horizontally.Aligning the webcam to the horizontal plane

2. Calibrate the SPA Polar-circle radius.

Tell SPA how big to draw the polar circle using the polarscope’s reticule as a guide.

Polar Circle Radius calibration

  1. Click on the “Calibration” button
  2. Click on the centre of the cross of the polar-scope’s reticule
  3. Click on the polar-scope’s polar circle
  4. SPA will draw a red circle over the top of the polar-scope polar circle. The radius of the circle will be updated.

3. Find the polar axis and draw the pole-star Hour Angle overlay

Using the telescope’s RA controls rotate the pole-star approximately 30 degrees around the axis of the telescope (this may not be the centre of the cross of the reticule if the reticule is not aligned ). Click on the pole-star.  Rotate the RA another 30 degrees or so and click the pole-star again. Rotate some more and make a final click.

With three clicks SPA calculates the correct polar-axis coordinates and draws the polar circle and pole-star hour angle.

  1. Click “Polar Centre” button
  2. Click on the pole-star
  3. Rotate the mount’s Right Ascension axis by about 30 degrees (2Hrs)
  4. Click on the pole-star
  5. Rotate the mount’s Right Ascension axis by about 30 degrees (2Hrs)
  6. Click on the pole-star
  7. Park the scope – (moves pole-star back to its original location).

4. Finally adjust the Mount

Use the Azimuth and Altitude bolts to place the pole-star in the red pole-star reticule.

SPA Features

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