AstorPearls - Astronomy Software
 Polar Alignment Part 3

Note

The Web contains a considerable amount of resources explaining drift alignment. You are highly encouraged to Google these and read them all. This article will give you a compact summary of what you need to do. It is a handy printout that you can carry with you to the field. Now, let’s begin…

What do you need?

You need a reticle:

  • You can either use real illuminated eyepiece (a good example is the one sold by Orion Telescopes).
  • A more affordable alternative is Reticulum from AstroPearls; it is a software reticle that you can use with your camera.

Preparation

Perform initial alignment mentioned in parts 1 and 2 of this article making sure mount is level and close to North. Using a polar scope will bring you very close to Polaris. It is crucial to make sure your mount is level.

Process

(I) Align your reticle with the East-West direction

Stars, as the sun do, appear to move from East to West. You need to align your reticle to this East-West direction. How to do this? Simple, with your tracking motor turned off watch a star moves on your field of view and rotate the reticle such that it is aligned with the path of the star. With this you caught two birds with one stone:

  • Your reticle is now aligned.
  • You determined your East-West directions. You can mark these directions on the reticle if you are using AstroPearls Reticulum Software. East is the direction towards which the star moves and vice versa.

You can also find the North-South directions by simply putting your hand or your flash light on the North side of the opening of the OTA, the reticle to the same side of your hand/flashlight is north and the opposite side is south.

(II) Adjusting Polar Axis Azimuth

To adjust the Polar Axis Azimuth (an East-West adjustment), we’ll follow these steps:

  • Choose a star close to the point where YOUR meridian intersects the celestial equator. With this specific selection, misalignment results in a considerable drift that you can observe and correct for.
  • Center this star and turn on your tracking to reduce RA drift as possible. We need to observe only Dec drift.
  • watch how the star drift against your reticle (it will be easier if you put the star on one of your East-West reticle lines):
    • If it drifts North, this means the polar axis is too far East.
    • If it drifts South, it means the polar axis is too far West.

Now, use your mount control to adjust the East-West pointing of the polar axis until you get rid of this North-South drift. Notice that the star can drift East-west as well due to RA error. Ignore this as it will be taken care of by the tracking (and Auto guide if you have it).

(III) Adjusting Polar Axis Altitude

This is the up-down tilt of the polar axis. To adjust it, follow the following steps:

  • Choose a star close to the eastern horizon. Again this choice will result in a considerable drift.
  • Make sure your reticle is aligned and N,S,E,W are determined as mentioned in step (I)
  • now, put the star on the reticle line and watch how it drifts in the North-South direction:
    • If it drifts North, it means that your polar axis has to much altitude and you need to lower it a bit.
    • If it drifts South, it means that your polar axis is too low and you need to increase its altitude.

Now use your mount controls to adjust the altitude until you eliminate the North-South drift.

You may need to repeat this process to fine tune your polar axis pointing until you reach the point where your object stay in place for as long as your exposure time will be. Now you are ready for astrophotography!