Re: [APML] Declination drift error quantified?

["Tom & Lou Krajci" <krajcit@3lefties.com>]

From: "Jerry Lodriguss" <jml@astropix.com>

> In a Web search....Covington....
>...the maximum declination drift for a 30-minute exposure with an
> alignment error of 2 arcminutes would be 15.7".  I don't imagine that the
> equation is so clean as to be linear (i.e. for an error of 1 degree, the
> drift is 30 times as high).

Yes, for small angles (like you'd expect for polar alignment...a degree or
two, and often less)...the equations scale almost in a linear fashion.  Yes,
for a 1 deg. azimuth error in polar alignment, you'd get about 30 times the
drift compared to a pointing error in azimuth of only 2 arcminutes.  (See
Dave Rowe's email/trig for the details.)

Still not convinced?...whip out your scientific calculator and take the Sine
of a small angle (1/2 degree for example) and make note of the value...then
take the Sine of 1 degree and 1/4 degree.  Yup...you'll see a nearly linear
relation there.  (It's most obvious when you set your scientific calculator
to use radians instead of degrees...then you'll find that Sin(x) = x is
almost true when x is small.)

Tom Krajci


--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>