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Sammyb

GOTO and tracking on equatorial or alt/az mounts

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Hello,

I was wondering about GOTO mounts and tracking.

The question I have is on an equatorial mount with GOTO is polar alignment also still necessary for tracking of objects - in addition to the alignment procedures in the mount?

Also - on alt/Az mounts for example on the celestron Nexstar 8SE - do these track objects without polar alignment?

Cheers,

Sam

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Hello,

I was wondering about GOTO mounts and tracking.

The question I have is on an equatorial mount with GOTO is polar alignment also still necessary for tracking of objects - in addition to the alignment procedures in the mount?

Also - on alt/Az mounts for example on the celestron Nexstar 8SE - do these track objects without polar alignment?

Cheers,

Sam

On an alt/az goto the requirements for accuracy are a properly levelled mount, location & time details. Then using one of the alignment options it can work out where it's pointing and how to move to the goto target. Bear in mind it can rotate, move left/right and up/down if aligned & levelled so no polar align is needed. You sort of set them as eq mounts with a wedge and do a polar align too though for accurate tracking for astrophotography etc.

On an EQ mount the axis are fixed, one of which is rotating around the polar axis so the polar fix is required.

Steve

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The main difference is that as you observe long-term on an alt-az mount, the objects within the fov will appear to rotate around the centre. On an eq mount they won't - they will remain in the same relative positions to each other.

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Thanks chaps. Thats very informative.

Polar alignment is still required for tracking on Equatorial GOTO mounts but the Alt/Az GOTO mounts will track an object however there will be rotaional effects after a time.

CHeers,

Sam

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Alignment is required for both, immaterial if EQ or Alt/Az.

Both need to have a known reference point. This is determined by the alignment procedure.

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Polar alignment is nothing to fear. It's really quite logical and very easy once you understand the principle.

It's purpose is to ensure that when tracking an object, the scope remains on target by driving the motors at the same rate as Earths spin, but, in the opposite direction. To effect this - the mount needs to remain pointed at polaris - RA and Dec axes take care of the scope orientation when pointing at different objects.

The big advantage is that this allows you to track in a single axis only (RA), because for any object the Dec axis will remain constant (assuming accurate PA). And that in turn makes it possible to do long exposure photography which is necessary for imaging faint objects (dso's).

An Alt/Az mount can't do this. It allways tracks with adjustments in Azimuth (left and right), and Altitude (up and down). One big advantage of Alt/Az mounts however is that they allow for very large aperture scopes - neccessary for light gathering power. You need that for observing objects with the naked eye.

To compare the tracking of both types of scope look at the Alt/Az and EQ grid lines in Stellarium. Speed up the rate a little, switch off the atmosphere, and watch how all objects follow RA but keep crossing Alt/Az lines :)

Edited by brantuk

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