If you're a newcomer to practical astronomy, you may have heard of people polar aligning their equatorial mount, and may be wondering what they're on about.
To understand why you need to polar align your equatorial mount, it's first necessary to understand what an equatorial mount does.
Earth takes 24 hours to complete one revolution on its axis with regard to the Sun.
However, because Earth also orbits the Sun, it takes 23 hours 56 minutes and 4.1 seconds to complete one revolution with regard to the stars.
From an observer’s point of view, the stars appear to move across the sky in an arc from east to west in the northern hemisphere and from west to east inthe southern hemisphere.
So if you are attempting to observe a celestial object like a star, planet or galaxy for an extended period of time - or if you are attempting to do long-exposure astrophotography of such an object - that object will drift out of your telescope's field of view.
An equatorial mount counters this by compensating for the apparent motion of the night sky cause by Earth's rotation.
It will allow you to track or follow a target across the night sky.
But an equatorial mount can't do this straight out of the box; it needs to be set up correctly in order to be able to operate from your particular location on Earth.
Therefore, to enable your equatorial mount to follow the movement of the sky, it’s necessary for the mount to rotate in the same plane as Earth by aligning it with the north and south poles.
This process is polar alignment, and you can find out more in our guide on how to polar align your equatorial mount.
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