Why Level the Mount?

Why is it necessary to level a mount before polar aligning it? Geometrically, when we polar aligns a
mount, it's quite possible to get the ra axis lined up accurately with the north celestial pole by
tweaking the altitude and az mechanical adjustments. The mount and telescope could even be
significantly unlevel. One might end up with the graduated altitude marks set significantly of from
one's actual latitude, but that wouldn't matter to the polar alignment. I can see where time might
be a consideration, but if, one is doing this with a computerized scope, the scope should be able to
handle it once one has synched and gotten the proper siderial time for the object. Perhaps there's
some mechanical consideration that makes it reasonable to keep the mount somewhat level? Torques
somewhere? It seems like one should be able to balance a scope in any odd ball position. It seems
that theoretically one could put a mount on a wall and still polar align it. It might be4 a bit
awkward, and some of the sky unaccessible but it still ought to work. Comments?

--
Wayne T. Watson (121.015 Deg. W, 39.262 Deg. N, 2,701 feet, Nevada City, CA)
-- GMT-8 hr std. time, RJ Rcvr

"...those of us alive today have about 625 times more lead in our
blood than people did a century ago." ... "many or our large
corporations are still making it (CFCs) in their plants overseas."
From Bill Bryson's A Brief History of Nearly Everything

Web Page: home.earthlink.net/~mtnviews
Imaginarium Museum: home.earthlink.net/~mtnviews/imaginarium.html

There is no technical reason to level the mount. However, the drift method
to fine tune polar alignment is much easier to do with a level mount because
elevation and azimuth are then independent of each other when doing fine
adjustments.

Chris L Peterson wrote:

On Mon, 11 Aug 2003 15:45:09 GMT, Wayne Watson wrote:


Why is it necessary to level a mount before polar aligning it?


Geometrically, it is completely unnecessary. The only reason you want the mount
roughly level is so that the altitude and azimuth controls you use for alignment
actually correspond to altitude and azimuth, and not some combination of the
two. But that really does only require rough leveling, within a few degrees.
There is absolutely no reason to spend more than about 30 seconds doing this-
just make sure the bubble isn't pinned against one side.

There's also the issue of the whole thing falling over if the balance is
grossly compromised ...

On Mon, 11 Aug 2003 15:45:09 GMT, Wayne Watson
wrote:

Why is it necessary to level a mount before polar aligning it?

Your analysis is correct. The *only* reason to level a GEM is to
facilitate drift alignment.

Wayne Hoffman
http://home.pacbell.net/w6wlr/
33° 49' 17" N, 117° 56' 40" W
"Don't Look Down"

Why is it necessary to level a mount before polar aligning it?

Hi:

It is not necessary.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

A portable, polar-aligned, level mount can (for visual purposes) be
accurately re-positioned on later nights (or even days) simply by
keeping the azimuth and altitude adjustments fixed; setting up the
tripod/mount at the same location, with the tripod feet arranged in
the same geographic alignment; followed by once again leveling the
mount.

IOW, in the scenario depicted above it's only necessary to polar align
using a polar alignment scope once. After that it's sufficient (at
least for visual purposes) to duplicate the tripod placement and level
the mount each time the telescope, tripod and mount are taken outside.

This method makes it easy to achieve accurate polar alignment even
when setting up in the daytime, in bright twilight, or when the north
celestial pole is unavailable due to clouds.

The bubble level in an EQ mount can be a practical and useful item --
at least for some people ;-)

Bill Greer

While others are right that it isn't necessary...there are three
reason why it is useful.
1. Faster setup the next time you set everything up...mark the tripod
locations for each leg for instance, polar alignment with a wedge will
be quicker since it will be closer to final alignment.
2. Azimuth and Altitude polar alignment corrections on the wedge will
be in one dimension...not too...thus a faster drift alignment session.
3. GOTO scopes..and especially those using digital setting circles
will be more accurate over the whole sky for ALT/AZ fork mounted
scopes or when they are on a wedge. Not important though for German
mounts.
Bob Berta

On 11 Aug 2003 21:43:58 -0700, (Robert Berta) wrote:

While others are right that it isn't necessary...there are three
reason why it is useful.
1. Faster setup the next time you set everything up...mark the tripod
locations for each leg for instance, polar alignment with a wedge will
be quicker since it will be closer to final alignment.

This strikes me as the most valuable reason to level carefully when using a
portable equatorial mount.

2. Azimuth and Altitude polar alignment corrections on the wedge will
be in one dimension...not too...thus a faster drift alignment session.

This is true, but the interaction between altitude and azimuth is insignificant
if you are leveled within a few degrees, which doesn't require any great effort.

3. GOTO scopes..and especially those using digital setting circles
will be more accurate over the whole sky for ALT/AZ fork mounted
scopes or when they are on a wedge.

Completely untrue in the case of wedge mounted scopes, which being equatorial
are independent of any leveling. There are perhaps badly designed altaz goto
scopes that depend on leveling. I experimented with my LX200 before putting it
on a wedge, and leveling had zero effect on pointing accuracy. In fact, I could
operate it in altaz mode while it was on the wedge. The pointing and tracking
accuracy was fine 40 degrees out of level.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Tue, 12 Aug 2003 05:05:31 GMT, Chris L Peterson
inscribed in blood upon a parchment:


3. GOTO scopes..and especially those using digital setting circles
will be more accurate over the whole sky for ALT/AZ fork mounted
scopes or when they are on a wedge.

Completely untrue in the case of wedge mounted scopes, which being equatorial
are independent of any leveling. There are perhaps badly designed altaz goto
scopes that depend on leveling. I experimented with my LX200 before putting it
on a wedge, and leveling had zero effect on pointing accuracy. In fact, I could
operate it in altaz mode while it was on the wedge. The pointing and tracking
accuracy was fine 40 degrees out of level.

I can second this. My LX-90 tracks and points fine even if it is only
levelled "roughly".

Best,
Dave


_______________________________________________ __

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Author of the Supernovae and Supernova Remnants FAQ
http://www.talkorigins.org/faqs/supernova/
Visions of Light, Visions of Darkness - B&W Photography of Wessex
http://www.valinor.freeserve.co.uk/visions.html

the angle of the polar
scope reticle will be off, and so will your polar alignment if you are
relying on the polar scope.

No. Not being level has no effect on the polar scope.

Roland Christen