This page
was updated in: June 12 '07, July 1 '14
The purpose of Polar Alignment is to point the Right Ascension axis (Polar Axis) of the telescope's equatorial mount to a Celestial Pole, enabling it to compensate for the rotation of the Earth and follow a fixed celestial object without adjusting the Declination.
This page offers information on how to accomplish the Polar Alignment of a Meade LXD55/75 telescope with the help of its Autostar computerized controller.
- It is recommendable to use a magnetic compass to orient the tripod to the Geographic North, considering the local magnetic variation.
- It is recommendable to use a bubble level to level the mount.
- It is required that Polaris is visible from the observing site.
(This is not the case in Caracas, except from the mountains to the north or south of the city)
(See "Adjusting the Elevation and Azimuth of the Polar Axis when Polaris is Not Visible From the Observing Site",
at the end of this page)
- It is required to know the date and time, longitude and latitude of the observing site.
(i.e. 10° 26' N, 66° 49' W, for El Hatillo, southeast of Caracas)
(The Autostar controller contains the positions for the main cities of the world)
See Geographic Names Server (GNS) (NGA Geographic Names Data: Coordinates).
- It is required that the polar telescope is aligned with the Polar Axis of the mount: The center of the image of a far away object does not move while changing the mount's Right Ascension.
- It is required that the main telescope is aligned with the Polar Axis of the mount: The center of the image of a far away object does not move while changing the mount's Right Ascension. When a far away object is centered in the polar telescope, it is possible to center it in the main telescope by adjusting the Declination to 90°.
- It is recommendable to use first low, and later high power eyepieces (preferably with an illuminated crosshair).
- It is recommendable to do a Precise Adjustment after accomplishing an Approximated Adjustment.
- It is recommendable to do at least one iteration after accomplishing a Precise Adjustment.
- In the southern hemisphere use the quadrangle formed by Sigma, Tau, Chi and Upsilon Octantis,
instead of Polaris. The iterative procedure is done with Sigma Octantis.
Approximated Adjustment of the Elevation and Azimuth of the Polar Axis:
1) Adjustment of the Base of the Equatorial Mount:
The base of the mount should be oriented in the north-south direction,
so that the Polar Axis of the telescope is in the plane of the local meridian.
The North leg of the tripod points North, the back legs point East-West.
For this orientation use a good compass,
taking care that it is not influenced by the metallic masses near to it,
like the telescope's mount and its base.
Take into account the variation of the Magnetic North with respect to the Geographic at the observing site
(in 2003, some 11° West for Caracas, 8° West for Mérida, 8° for Maracaibo,
9° for Barquisimeto, 10° for Valencia, 12° for Margarita, Pto. La Cruz and Pto. Ordáz).
The compass will indicate the Azimuth of the Celestial North Pole (and the Geographic North).
See Introduction to Geomag (U.S. Geological Survey)
and Magnetic Declination Calculator (Natural Resources Canada).
For the adjustments of Azimuth and Elevation of the mount to be independent, the mount's base must be horizontal both in the East-West and the North-South directions. This is accomplished by carefully adjusting the length of the tripod's legs, placing the bubble level on the base, for each direction.
Check these two levels for the fully assembled telescope (it is convenient to make a preliminary adjustment of the Azimuth and Elevation of the Polar Axis, to compensate for the effect of its weight on the base and legs). Check this levels every time you move the base.
2) Approximated Adjustment of the Elevation and Azimuth of the Polar Axis:
Adjust the telescope's mount for an Elevation approximately equal to the latitude of the observing site
using the elevation scale and the adjustment screws.
(The latitude determines the Elevation of the Celestial North Pole)
[To allow the passing of the bar and counterweights in front of the north leg of the tripod in latitudes lower than some 6°,
it is necessary to shorten the north leg instead of lowering the Elevation of the mount.
This unlevels the base of the mount in the North-South direction
and makes the Elevation and Azimuth adjustments interdependent,
but does not affect the quality of the Polar Alignment.]
With the main telescope pointing either East or West, adjust the Elevation and Azimuth screws of the mount
so that Polaris (RA 2h 32m, Dec 89° 16' N, Epoch 2000) is in the crosshairs of the polar telescope's reticule.
This requires the polar telescope to be aligned with the mount's Polar Axis.
The mount's Polar Axis now points, with a 45' error or less, to Dec 90° N; the Celestial North Pole.
This error will be corrected by the Precise Adjustment.
Change the Declination to 90° N and manually adjust it to center Polaris in the main telescope.
This requires the main telescope to be aligned to the polar telescope.
(The Declination motor should be on the West side)
Finely adjust the Declination, Azimuth and Elevation so that you can move the telescope in Right Ascension while Polaris remains centered
in the field of view of the finder telescope. Refine by using the main telescope, starting with low power and then increasing it.
- The mount is now in its "Home Position" for Declination.
Adjust the Right Ascension so the counterweight bar is vertical.
This requires that the mount is level in the East-West direction.
- The mount is now in its "Home Position" for Right Ascension and Declination.
Turn the Autostar ON and initialize it with the correct date, time and observer position.
(See the Instruction Manual; Before the first use and after a Reset the Autostar must be Trained and Calibrated)
The adjustment of the Elevation angle of the Polar Axis should not have to be modified if the latitude of the observing site does not change more than some 2 Km North or South of the original site (more than 1'), but in practice it depends on the flexibility of the tripod's legs.
3) Locating Objects [GOTO]:
In this condition, the telescope, with the lowest power eyepiece,
should be able to locate, with little error in Right Ascension and Declination, any celestial object.
After locating with [GOTO] a fixed celestial object, we can center it and synchronize the Autostar controller
(pressing [ENTER] twice) so it indicates the correct position for this object and its surroundings.
Locating with [GOTO] planets and other moving celestial objects is of lower precision.
It is not recommended to synchronize with them.
You may use the
ARVAL Catalog of Guide Stars
to obtain the names and positions of the brightest stars.
And for other classes of objects,
the other sections of the ARVAL Catalogue of Bright Objects.
The Autostar controller contains references for all of these objects and for many more of lesser brightness.
4) Testing:
In this condition, the telescope, with a low power eyepiece,
should be able to track for tens of minutes, with little adjustment in Declination or Right Ascension,
any fixed celestial object, after turning ON the Right Ascension tracking mechanism.
This happens after attempting to locate with [GOTO] the first celestial object with the Autostar.
Mark the positions of the legs of the tripod, to facilitate repositioning the telescope without losing the approximate alignment (always check the level of the base).
It is recommended to make a Precise adjustment after accomplishing an Approximate Adjustment.
Precise Adjustment of the Elevation and Azimuth of the Polar Axis:
It is required to use the "One-Star" alignment of the Autostar controller.
The "Easy", "Two-Star" and "Three-Star" procedures are no help for this adjustment,
as they only correct the positions generated by the Autostar
to compensate for the error in the Polar Axis alignment and increase the precision of the [GOTO] function.
Perform this Precise Adjustment after finishing an Approximate Adjustment.
Select "One-Star Alignment" in the Autostar.
Press [ENTER] to accept that the Declination is 90°
when Polaris is centered in the main telescope.
In reality it is 45' (or less) off 90° N, the true "Home Position" in Declination.
The Autostar selects Polaris and the telescope moves to RA 2h 31.8m, Dec 89° 16' N.
With the screws, adjust the Azimuth and Elevation of the mount to center Polaris in the eyepiece.
Press [ENTER].
An alignment star is selected by the Autostar. Then the telescope moves towards it,
center it using the Autostar. Press [ENTER].
(The Autostar controller allows you to select another star
in case the first one selected is not visible from your site)
The Autostar calculates to approve or disapprove the alignment.
If the alignment is disapproved, check that you have followed all the recommendations in the first section of this document, that you have followed the correct procedure, and that there are no electrical or mechanical problems.
Iterative Procedure:
If the alignment is approved, do a [GOTO] to Polaris (SAO 308),
correct for 2/3 of the error in Alt. and Az. using the screws in the mount, not the controller.
Then do a [GOTO] to the alignment star, center it with the controller,
and synchronize it (pressing [ENTER] twice).
Repeat using shorter eyepieces (preferably with an illuminated reticule)
until you can [GOTO] between Polaris and the alignment star with almost no error.
It is recommended to do at least one iteration after accomplishing a "One-Star" alignment.
See
"Polar Alignment by Iterating on One Star and Polaris",
Michael A. Covington, Artificial Intelligence Center, The University of Georgia.
(Adobe Acrobat document, PDF)
You can improve the alignment by reiterating the procedure until you obtain a tracking precision,
without Declination error, of tens of minutes with maximum power in the telescope.
But for photographic purposes of long exposures it is recommended to accomplish the
Refined Adjustment by Drifting procedures described later in this page.
For photographic purposes of long exposures it is required that the telescope can follow the object for the duration of the exposure without making corrections in Declination, only in Right Ascension. This avoids the phenomenon called "Field Rotation".
The Autostar controller allows you to make a constant correction on the Right Ascension tracking mechanism. Other variable or periodical errors in Right Ascension can be manually corrected with the controller, adjusted for "1X" speed.
The Meade Lunar and Planetary Imager (LPI) [discontinued]
can be used for automatic guiding when it is mounted on an "off axis" prism,
or the direct capture and processing of color or black and white digital images
when it is mounted at prime focus.
These requires a Windows PC to run the included Autostar Suite;
image capture/processing, and Meade Autostar telescopes local or remote control software.
The LPI camera is based on a CMOS chip that produces 640 x 480 pixels images,
with a coverage similar to that of a 6 mm eyepiece. It will capture images on any telescope.
The camera connects to a USB port, and the Meade telescope guiding system, to a serial port (RS-232).
The remote control is through a local area network or the Internet.
See Observatorio ARVAL - Astrophotography with the Meade LPI Digital Camera
Refined Adjustment by Drifting of the Elevation and Azimuth of the Polar Axis:
- The Refined Adjustment by Drifting procedures are generally required only for photographic purposes, but they can be used to perfect an approximated alignment.
- The Refined Adjustment by Drifting procedures are indicated for observing sites with a Northern latitude; Inverting the North and South directions of the drifts they can be used for Southern latitudes.
1) Refined Adjustment of the Azimuth of the Polar Axis:
Point the telescope with a high power eyepiece (preferably with an illuminated reticule),
to a star with Declination near 0° (within ±5° if possible)
and near the Meridian (within ±0.5 hrs of RA if possible).
Follow this star during a few minutes noting the direction of its Declination drift (correct and disregard any Right Ascension drift).
- If the star drifts to the South, the Polar Axis of the mount points too far East.
- If the star drifts to the North, the Polar Axis of the mount points too far West.
Correct the Azimuth of the Polar Axis to stop any Declination drift.
2) Refined Adjustment of the Angle of Elevation of the Polar Axis:
Point the telescope with a high power eyepiece (preferably with an illuminated reticule),
to a star with Declination near 0° (within ±5° if possible) and near the Eastern Horizon
(with an Elevation somewhat greater than 20° if possible).
Follow this star during a few minutes noting the direction of its Declination drift (correct and disregard any Right Ascension drift).
- If the star drifts to the South, the Polar Axis of the mount points too low.
- If the star drifts to the North, the Polar Axis of the mount points too high.
Correct the Elevation of the Polar Axis to stop any Declination drift.
3) Testing:
In this condition, the telescope, with a high power eyepiece (preferably with an illuminated reticule),
should be able to track for tens of minutes, with no adjustment in Declination,
any fixed celestial object, if we correct with the Right Ascension tracking mechanism.
This alignment should be refined by reiterating this procedure until you get the required precision for the planned photographic purposes (in general, no adjustment in Declination and little in Right Ascension during an exposure).
The Autostar controller allows you to make a constant correction on the Right Ascension tracking mechanism. Other variable or periodical errors in Right Ascension can be manually corrected with the controller, adjusted for "1X" speed.
The Meade Lunar and Planetary Imager (LPI) [discontinued]
can be used for automatic guiding when it is mounted on an "off axis" prism,
or the direct capture and processing of color or black and white digital images
when it is mounted at prime focus.
These requires a Windows PC to run the included Autostar Suite;
image capture/processing, and Meade Autostar telescopes local or remote control software.
The LPI camera is based on a CMOS chip that produces 640 x 480 pixels images,
with a coverage similar to that of a 6 mm eyepiece. It will capture images on any telescope.
The camera connects to a USB port, and the Meade telescope guiding system, to a serial port (RS-232).
The remote control is through a local area network or the Internet.
See Observatorio ARVAL - Astrophotography with the Meade LPI Digital Camera
Adjusting the Elevation and Azimuth of the Polar Axis
when Polaris is Not Visible From the Observing Site:
From an observing site with a view of Polaris and as close as possible,
make an Approximate Adjustment of the Elevation and Azimuth of the Polar Axis,
with special attention that the base of the mount is horizontal,
both in the East-West and North-South directions.
Mark on the mount the position obtained for the 90° N Declination.
Preserve as well as possible the Approximate Adjustment for the Elevation and Azimuth of the mount.
On the observing site with no view of Polaris,
mount the telescope with special attention that the base of the mount is horizontal,
both in the East-West and North-South directions.
Carefully adjust the North-South orientation of the mount.
You can use a distant Landmark (Terrestrial Target), entered after a successful alignment, as a referenece.
Set the telescope to the 90° N Declination using the mark you made on the mount.
- The mount is now in its "Home Position" for Declination.
Set the Right Ascension axis so that the counterweight bar is vertical.
- The mount is now in its 90° N for Right Ascension and Declination.
Turn the Autostar ON and initialize it with the correct date, time and observer position.
Iterative Procedure:
Do a [GOTO] to a star with Declination near 0°
(within ±5° if possible) and near the eastern horizon.
Correct the Azimuth of the mount so that the star is as close as possible
to the center of the field visible on the telescope.
Do a [GOTO] to a star with Declination near 0° (within ±5° if possible)
and near the Meridian (within ±0.5 hrs of RA if possible).
Correct the Elevation of the mount for the star to be as near as possible
to the center of the field visible in the telescope.
It is recommended to refine this alignment,
reiterating this procedure until you get the tracking precision required for the planned purposes
(in general, no adjustment in Declination and little in Right Ascension during an observing period).
In this condition, the telescope, with an eyepiece for the lowest power,
should be able to locate, with little error in Right Ascension and Declination, any object in the sky.
After locating with [GOTO] a fixed object in the sky, we can center it and synchronize the Autostar controller
(pressing [ENTER] twice) so it indicates the correct position for this object and its surroundings.
Locating with [GOTO] planets and other moving celestial objects is of lower precision.
It is not recommended to synchronize with them.
It is recommended to additionally accomplish the Refined Adjustment by Drifting procedures.
Note: This is the procedure you can use during the day,
but the selection of alignment stars is restricted to the brightest of them.
Meade LXD55/75 Series with Computerized Autostar Controller:
| Model | Type | Aperture | Focal Length | Power / Field * |
|---|---|---|---|---|
| SN-6 AT | ||||
| SN-8 AT | ||||
| SN-10 AT | ||||
| AR-5 AT | ||||
| AR-6 AT | ||||
| SC-8 AT |
* With the standard 26 mm Super-Plössl eyepiece.
Note: The "EC" suffix in some models, not shown here,
indicates the simple electronic controller, without a computer.
Websites with information on Meade LXD55/75 telescopes:
Meade Instruments Corporation
- Support / Manuals / Meade Instruments
LXD55 Yahoo Group
Meade Advanced Products Users Group (MAPUG) [discontinued]
Weasner's LXD55 Site [discontinued on May 2008]
This page
was updated in: June 12 '07, July 1 '14
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Spanish: Alineación Polar para los telescopios Meade LXD55/75 con Autostar
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