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Even though the NexStar can precisely track a celestial object while in the Alt-Az position, it is still necessary to align
the polar axis of the telescope (the fork arm) to the Earth's axis on rotation in order to do long exposure astro
photography. To do an accurate polar alignment, the NexStar requires an optional equatorial wedge between the
telescope and a tripod. This allows the telescope's tracking motors to rotate the telescope around the celestial pole, the
same way as the stars. Without the equatorial wedge, you would notice the stars in the eyepiece would slowly rotate
around the center of the field of view. Although this gradual rotation would go unnoticed when viewing with
an
eyepiece, it would be very noticeable on film.
Polar alignment is the process by which the telescope's axis of rotation (called the polar axis) is aligned (made parallel)
with the Earth's axis of rotation. Once aligned, a telescope with a clock drive will track the stars as they move across
the sky. The result is that objects observed through the telescope appear stationary (i.e., they will not drift out of the
field of view). If not using the clock drive, all objects in the sky (day or night) will slowly drift out of the field. This
motion is caused by the Earth's rotation.
Whether you are using your NexStar in the Alt-Az configuration or polar aligned, it will be necessary to locate where
north is and more specifically where the North Star is.
The polar axis is the axis around which the telescope rotates when moved in right ascension. This axis points
the same direction even when the telescope moves in right ascension and declination.
Definition
Figure 6-3
This is how the telescope is to be set up for polar
alignment. The tube should be parallel to the
fork arm and the mount should point to Polaris.
Summary of Contents for NexStar 5
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