In article <e7ydnZssFdageM7ZnZ2dnUVZ_u-dnZ2d@xxxxxxxxxxxx>,
Fred Scharmann <fjs2spam@xxxxxxxxxxxx> wrote:
> Since I am new to this all, you are probably right.
> All I know is that if I level my mount and do a polar alignment, chasing
> something at 200X is one hell of a lot easier than if I am "almost" level
> and do a polar alignment. Maybe the problem of semantics is occurring in
> the definition of polar alignment. You and I may be talking about apples
> and oranges. Since I am a beginner, my thoughts about polar alignment may
> be incorrect and you being experienced, probably actually know what is meant
> by polar alignment.
> Whatever the problem, I find your responses to my posts as negative and
> non-constructive. If you know more than me, which is very, very possible,
> teach me. Don't attack me! Why is leveling so unimportant to you?
Because what matters is how well your polar axis is aligned. Nothing
else - the levelling is in principle unimportant.
How do you align your polar axis? Do you adjust your wedge to your
latitude and then align the telescope azimuth to the north? If so,
your method of polar alignment is dependent on your levelling, and
the reason you find chasing something at 200x a hell more difficult
when your scope is only "almost level" is not because it's not quite
level, it's because your scope is then not polar aligned properly.
Polar alignment only means your polar axis points to the celestial
pole - nothing else.
So how do you determine whether your scope is polar aligned or not?
The traditional method is to turn on the scope drive, then let the
scope follow a star near your local meridian. If the star appears to
drift northwards or southwards, adjust the azimuth of your polar axis
until that drift vanishes. Next, let the scope follow a star near +6
or -6 hours of local hour angle -- i.e. approximately in the east or
west. If the star appears to drift northwards or southwards, adjust
the inclination of your polar axis until the drift vanishes. Go back
and forth between following a star near the meridian and
approximately in the east or west, until you're satisfied with your
polar axis alignment. This method takes some time, and is therefore
most suitable for permanently mounted scopes, but it will give you
the most accurate polar alignment.
A faster method, which I use myself, is to learn the star field near
the celestial pole, or get a good star map of that field, so you
easily can see where the celestial pole is in that star field. Note
that, due to precession, the celestial pole moves slowly - this
should be marked on that chart if you want an accurate polar
alignment. Next, set your scope to +90 deg declination and +6 (or
-6) hours local hour angle. Look through your finder scope, adjust
your polar axis so that the crosshairs of the finder scope points at
the celestial pole. Next, turn your scope 12 hours in RA, look
through your finderscope again. Most likely, the crosshairs will
point somewhere else, and that's because your scope didn't point to
precisely 90 deg declination in its mounting. Adjust the scope's
declination until the crosshairs of the finder scope points to
precisely the same position in the sky no matter how you turn the
scope in RA. Now the scope points parallell to the mounting's polar
axis, so all you have to do is to adjust its polar axis until the
crosshair of the finder points right at the celestial pole. (This
method cannot be used near the equator of the Earth).
None of these two methods depends on any "levelling" of anything on
the scope. Polar alignment is actually independent of levelling,
although some methods of polar alignment can be dependent on
levelling -- such methods don't give very accurate alignment though.
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se