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EQ mounts require two types of alignment.
The first one (1-, 2- or 3-star alignment) tells the mount which way it is oriented in space. After successfully completing this kind of alignment the mount will be able to GOTO objects.
The second kind is polar alignment, it means making the mount's RA axis parallel to the Earth's axis of rotation. This is required for tracking (following objects as the move across the sky).
Polar alignment is not required for a successful 2- or 3-star alignment. The mount will be able to GOTO objects regardless. However, it will not be able to keep objects in the field of view for extended periods of time.
It is only that way because of a design choice made my the manufacturer. After 2- or 3-star alignment the mount knows the polar alignment error and could automatically compensate for it. This would require using both the RA and Dec motors for tracking. Mounts like the NEQ6 (and many other EQ mounts) only track using the RA motor, hence the requirement for polar alignment.
Interestingly, Alt-Az mounts like the AZ-EQ6 are perfectly capable of tracking using both RA and Dec motors. This will cause field rotation of course, and would therefore be unsuitable for most imaging purposes. However, Synta have no HEQ5Pro or NEQ6 caliber Alt-Az mounts in their line-up that would suit visual astronomers. The AZ-EQ6 is more expensive than the NEQ6, which is why a lot of visual observers put up with the quirks of EQ mounts.
Cheers
Steffen.
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