On Mon, 26 Oct 2020 09:41:11 +0100, Björn Lundin 
declaimed the following:

>
>Is that true also for planets?
>I get that it correct for stars and deep sky objects,
>but planet evolve around the sun, not polaris
>

 The problem is that the EARTH is what is rotating. When you polar align
an equatorial mount, you line up one axis with the axis of the earth. In
that configuration, while the earth is rotating in one direction, the
telescope is rotating in the opposite -- and since the axes are parallel,
any distance above/below the equator stays the same (so no adjustment
needed in declination).

 Using an alt/az mount means you have no axis parallel to that of the
earth (unless you set up the telescope at either the N or S pole itself!).
As you follow objects across the sky, the two axes of the telescope keep
changing orientation relative to the object. Difficult to illustrate in a
text-only medium but...

 That equatorial mount, on the equator, will appear to the user to be
completely on its side.

)|

(where ) is the curve of the earth, and | is the RA axis of the scope). In
contrast, the alt/az axis will be

)--

and there is no way to point a scope tube at the end of that axis that can
compensate for earth rotation.

https://www.celestron.com/blogs/knowledgebase/what-is-field-rotation-how-does-i
t-affect-my-scope-s-viewing-and-imaging

 Due to so many scopes now being sold with alt/az mounts (for visual
usage, the computer controls on these models is able to track both alt and
azimuth) there are
https://telescopes.net/store/telescope-accessories/astro-imaging-accessories/fi
eld-de-rotators.html
which are motorized to compensate (ignore the William Optics entry -- from
what I see that is a manual rotator which means you have to nudge it during
the exposure; more suited for easily rotating a camera so the long side of
the sensor fits the object better).

 More information than you care for at
https://telescopemount.org/alt-az-mounts-for-long-exposure-astrophotography-cam
era-rotators/
along with the embedded linked articles.


>As you may have noticed - I am a novice in this field.


--
 Wulfraed                 Dennis Lee Bieber         AF6VN
 wlfraed@ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/

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