Re: Mount RA/DEC slew math


Ray Gralak
 

Why is that? Isn't Alt:0 Az:90 and Alt:0, Az:270 on the same RA plane?
Does the RA axis actually move, or are you relying on where the camera is aiming to detect RA movement? If it is the latter and the camera is not orthogonal, then a 180-degree flip will not be exactly 180 degrees offset from its starting point.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of deonb
Sent: Saturday, December 26, 2020 11:39 PM
To: main@ap-gto.groups.io
Subject: [ap-gto] Mount RA/DEC slew math

I'm trying to correct my pier's N/S and E/W positions in my dome, so I stuck a camera in the middle of my scope's lens
cap and ran a tape marker down the length of the dome shutter. I'm then trying to align one axis at a time.

I thought that if I slew from Alt:0 Az:90 to Alt:0, Az:270, the mount will only slew DEC without moving RA. And if the
dome alignment is correct, it should move in a curved track around the dome and come to land in the middle of the
shutter tape on the other side.

That's the theory... In practice what happens is that the RA axis also moves during this slew. Not a lot, but enough to
make my doubt my hypothesis.

Why is that? Isn't Alt:0 Az:90 and Alt:0, Az:270 on the same RA plane?

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