Re: leveling a tripod

In article <1146381489.858029.43870@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
atasselli@xxxxxxxxxxx <atasselli@xxxxxxxxxxx> wrote:

Stephen Paul wrote:
Fred Scharmann wrote:
Why is leveling so unimportant to you?

Thinking otherwise is a common misunderstanding...

Quite the opposite...

The polar axis of a mount is an imaginary line that extends from the
azimuth pivot of the mount to the celestial pole. Everything in the sky
rotates around this axis.

The azimuth pivot is the axis the equatorial head rotates about when
adjusting the azimuth. It is NOT the RA axis which is the one that
needs to be aligned to the celestial polar axis.

Andrea T.

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 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
WWW: http://stjarnhimlen.se/
.

Relevant Pages

  • Re: leveling a tripod
    ... All I know is that if I level my mount and do a polar alignment, ... Because what matters is how well your polar axis is aligned. ... it's because your scope is then not polar aligned properly. ...
    (sci.astro.amateur)
  • Re: Setting up a telescope to polar alignment - problems with Bresser Skylux
    ... Skylux with a German mount and needs to be set up with polar alignment. ... Once the MOUNT is polar aligned, the SCOPE will ... little setting circle down (if it doesn't rotate independently of the ...
    (uk.sci.astronomy)
  • Re: faliure so far trying to see mars
    ... If it's an SCT or a reflector, ... Have you allowed enough time for the scope to cool. ... >>>couple of hours outside in the dark will normally sort that issue out ... >>>polar cap or two (the North Polar Hood should be visible but the South ...
    (uk.sci.astronomy)
  • Re: faliure so far trying to see mars - Mars2.jpg (0/1)
    ... If it's an SCT or a reflector, ... Have you allowed enough time for the scope to cool. ... >>>couple of hours outside in the dark will normally sort that issue out ... >>>polar cap or two (the North Polar Hood should be visible but the South ...
    (uk.sci.astronomy)