[billdan (Bill)]

Hi

I'm a little bit confused about sidereal rate, a thread was just started on Cloudy Nights about refraction and sidereal rates. Its off the air now so I can't read the conclusions.

It appears that the 15.041 arcseconds per sec rate is only applicable at when pointing at zenith. Any altitude below Zenith, refraction of the air slows this rate down and is slowest at the horizon.

Apparantly you have to calculate a 'King' rate to compensate for this.

So does my Synscan controller do this in firmware based on its internal pointing model?

My drift alignment is now spot on and I can turn DEC guiding off, but it appears I will still need RA guiding to compensate for the change in Sidereal rate. ( discounting PEC errors)

Confused

Bill D