For a telescope to accurately track the sky motion of any celestial object like planets, stars, and deep-sky objects, precise polar alignment is needed. This is true for any equatorial telescope, both for manual and electronic types. Without proper polar alignment, objects will always drift out of view making it impossible to perform lengthy and detailed observations. In astrophotography, poor polar alignment would mean sad-looking star trails in captured images.

To polar-align your telescope, first, we need to find the pole star, Polaris.

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Finding Polaris using the stars of the Big Dipper

Since the Philippines is located approximately 15 degrees above the equator, Polaris should be approximately 15 degrees from the northern horizon. You may use the 2 bright stars of the Big Dipper in locating Polaris. Point the telescope’s polar axis towards Polaris to achieve rough polar alignment.

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A telescope with its polar axis pointed towards Polaris

For more precise alignment, most telescope mounts nowadays feature what is called a polar scope, a type of ‘finder scope’ placed in the polar axis of a telescope to help check alignment with the pole star (Polaris).

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A telescope mount with a polar scope

Looking through the polar scope, you should see a star map with markings similar to the one below.

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Looking through a polar scope

Since the polar axis of the Earth does not exactly point at Polaris, polar scopes are provided with a calibrated star map. The idea is not to position Polaris exactly at the center, but instead, on a pre-defined location (off-center) on the star map.

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Polaris must be centered in a pre-defined spot

This calibrated star map must correspond to the actual position of sky objects. Rotate the star map by turning the polar scope’s barrel clockwise or counter clockwise.

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Rotate the star map to correspond to the stars’ actual position

You can then make fine adjustments with the mount to help center Polaris in the pre-defined spot. Most telescope mounts with polar scopes have knobs to move the polar axis (along with the polar scope) in an up-down and left-right direction.

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Adjustment knobs for moving the polar axis of the telescope’s mount

Adjust the knobs (turn) as necessary. Precise polar alignment is achieved by centering Polaris in the pre-defined spot in the calibrated starmap.

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Polar alignment achieved with the help of a polar scope, with Polaris carefully centered in the pre-defined spot.

A polar-aligned telescope should be useful enough for visual observations and most lunar, solar, and planetary imaging. For more precise polar alignment required in deep-sky (long-exposure) astrophotography, read more about the advanced technique called Drift-Alignment Method.

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For DIY astronomy projects useful for astrophotography, click here.
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© Anthony Urbano (Manila, Philippines)

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