When I started out with Astronomy with its miriad of equipment, I struggled to initially fully understand what Polar Alignment was and why it is so important so this article is here for those of you newbies who would like a clear explanation as to what it means and some differing ways of achieving it.

So lets think about the basics and fully understand them – think about the night sky differently. The stars do not rotate or change their position, our earth does. We are are in an orbit around our sun and our planet rotates on a North/South axis around the celesestrial poles as it orbits the sun. Its a bit like a ball (the earth) with a stick stuck through it, rotating on that stick, like a spinning top. Where the stick goes through the ball are the “poles” around which it rotates… each complete rotation is of course a day.

Our seasons come from the tilt of the stick, whichever hemisphere tilts towards the sun gets more direct energy and light and enjoys summer and vice versa. So from the north and southern hemispheres you get to see a different patch of the universe from the ground depending on where you are and what time of year it is.

Alt-azimuth mounts (short for altitude-azimuth) allow a telescope to move up-down and left-right.  This movement is parallel and perpendicular to the horizon, making this mount intuitive to point, leaving the eyepiece in a convenient position, and making it well-suited to terrestrial observing. However, it makes tracking objects in the sky more difficult; automatic tracking is only possible with a computerized telescope. 

A German Equatorial mount (GEM), on the other hand, has its axes aligned with Earth’s rotational axis, allowing easy automatic tracking of the night sky.  Disadvantages include less intuitive pointing, more weight, and sometimes an awkward eyepiece position (but we don’t use them anyway, do we?)  For accurate tracking, especially for astro photography, an equatorial mount is therefore essential.

The polar alignment procedure works on one simple principle: The polar axis of the telescope must be made parallel to the Earth’s axis of rotation, called the North Celestial Pole (NCP). When this is accomplished, the sky’s motion can be cancelled out simply by turning the axis (either by hand or with a motor drive) at the same rate as the rotation of the Earth, but in the opposite direction. 

As you head further south (something you can’t fail to do when moving away from the North Pole!) the position of the NCP appears to get lower in the northern part of the sky. In fact if you travelled all the way down to the equator, the NCP would appear on the north point on the horizon with its Southern Hemisphere counterpart, the South Celestial Pole (SCP) visible on the southern point on the horizon.

The great thing about German Equatorial Mounts is that once you Polar align and tell your mount exactly where it is and what the time it is, most modern mounts have a GoTo computer that will point your telescope accurately at the chosen object and precisely track it. In addition we can use Guiding (via additional software and camera) to ensure even the manufacturing tolerances of the worm gears or belts in your mounts (backlash) are handled and cancelled out giving nice clean stars with no trails over long exposure times.