Hall's Harbour Observatory,   Hall's Harbour, NS

HEQ5 Polar Alignment

21-Nov-2017, 19:06 AST 21-Nov-2017, 23:06 UTC

Introduction

The task of orienting the polar scope is greatly hindered by the fact that the HEQ5 manual is full of mistakes. If you already know how to do a polar alignment, you probably don't need the manual and won't notice the mistakes. On the other hand, if this is your first precision mount, you probably will need the manual, and it will certainly confuse you. You simply cannot do the alignment if you follow the manual. In fact, following the manual is literally impossible - among other problems, it requires the setting circle to be in two different places at once. So, ignore anything in the manual that relates to polar alignment.

This procedure is biased towards observers in the Northern Hemisphere. Sorry, southies! It took me three days to work out this procedure. I haven't yet had the time to work out the southern hemisphere equivalent.


In these procedures, I use the same component names that the HEQ5 manual describes in Figure h-1 on page 11.


(Click on thumbnails
to enlarge.)

The nightly polar alignment is what you do at the beginning of each observing session. It is best performed with the telescope and counterweights removed from the mount. Here are two procedures for doing the polar scope alignment. The two procedures are:

  1. Using the current hour angle of Polaris, which you obtain from software. Two sources are described below:
    1. SynScan hand controller
    2. Stellarium (or similar software)

  2. Without knowing the hour angle of Polaris, using the date scale on the polar axis of the mount.

Of the two, the first method is much faster and simpler.


Nightly alignment with SynScan


  1. If your hand controller is set up with your correct Latitude, Longitude and Time Zone, obtain the current hour angle of Polaris from it. The menu steps are:
    • Utility Func
    • Show Information
    • Polaris Pos
    In the example at right, the hour angle of Polaris is 14:13.
  2. Then proceed to the "Nightly Alignment with Hour Angle" section, below.

Nightly Alignment with Stellarium or other similar software

  1. Ensure the software is set to your location and the current time. Select Polaris and note its Hour Angle.
  2. Then proceed to the "Nightly Alignment with Hour Angle" section, below.

Nightly Alignment with Hour Angle

For this procedure, you do not need to orient the Polar Scope Reticule, as described below, since you will not be using the Date Scale Index Marker. However, you should still have performed the Aligning the Polar Scope Reticule procedure. It only needs to be done once, unless you have removed the polar alignment scope from the mount.

  1. Completely ignore the Date / Longitude Scale and its Index Mark. You will not be using them. Lock the RA setting circle at zero.

    The manual does not mention that there is a drilled hole in the RA Setting Circle to positively lock the circle at zero. Though you can friction-lock the circle at any setting, screwing the setscrew into the drilled hole establishes a more positive lock while rotating the mount.


  2. Looking through the polar scope, rotate the RA axis so that the “Polaris” marking is at the bottom (6 o'clock position) of the image. Lock the RA axis.

    If you wish more accuracy than just eyeballing the 6 o'clock position, move the mount until Polaris is exactly centered on the cross-hairs. Now use the latitude adjustment screws to move Polaris down to the 6 o'clock position on the large circle. Rotate the mount in RA so that Polaris is centered in the small circle. Continue with the next step below.


  3. Unlock the RA setting circle. Now, unlock the RA axis and rotate it until the hour angle shows the current hour angle of Polaris, as determined from the handset or software. Read the hour angle on the LOWER scale in the Northern hemisphere and the UPPER scale in the southern hemisphere. Note that this use of scales is the opposite of what is used elsewhere. The example at right shows an hour angle of 14:32.

  4. The polar scope is now aligned. The marked positions of Casseopeia and the Big Dipper in the Polar scope will now correspond to the directions of those constellations in the sky. (You will not see the stars of those constellations in the polar scope.) This serves as a check that you have not made any gross errors in the process.

  5. Complete your polar alignment by using the azimuth and altitude (latitude) adjustments to center Polaris in the indicated circle in the reticule of the polar scope. You are almost finished... Go to the Home Position section.

Nightly Alignment without Hour Angle

Use this procedure if you do not know the current hour angle for Polaris. It uses the Date and RA Scales to determine the appropriate orientation of the mount, in effect computing Polaris' hour angle.

  1. Before you do this procedure for the first time, you must have completed the One-Time Setup of the polar scope. Assuming you have completed that procedure, carry on here for your nightly alignment.

  2. Rotate the RA axis so the Longitude Index Mark is on the top side of the mount. Note that no precision is required in this step. It is simply to get the Longitude Index Mark into a convenient location for the next step. Lock the RA axis.

  3. Turn the Date / Longitude scale so your Longitude Offset lines up with the Longitude Index Mark. Unless you moved the Date / Longitude Scale accidentally since your last alignment (or this is the first time you have done this procedure), it will already be there. This step is just to ensure that it is. In the example at right, the location is 5º west of the centre of the time zone.

  4. Unlock the RA axis and rotate the mount so the Date Scale / RA Setting Indicator is pointing at the current date on the Date Scale. Lock the RA axis. In the example at right, the date is July 15th.

  5. Loosen and move the RA Setting Circle to show the current Standard Time on the Date Scale / RA Setting Indicator.. (If you are currently on Daylight Saving Time, subtract an hour from the clock time.) Use the upper scale in the Northern hemisphere and the lower scale in the Southern hemisphere. [Contrary to what the manual says, do not lock the setting circle.] The illustration below shows 22:00 DST (21:00 Standard Time) on July 15th.

  6. Unlock the RA axis and rotate the mount until the Date Scale / RA Setting Indicator points to zero on the RA Setting Circle. Lock the RA axis. The reticule is now in the proper orientation.

  7. The polar scope is now aligned. The marked positions of Casseopeia and the Big Dipper in the Polar scope will now correspond to the directions of those constellations in the sky. (You will not see the stars of those constellations in the polar scope.) This serves as a check that you have not made any gross errors in the process.

  8. Complete your polar alignment by using the azimuth and altitude (latitude) adjustments to center Polaris in the indicated circle in the reticule of the polar scope. You are almost finished... Go to the Home Position section.

Home Position.

"Home Position" is the position in which the OTA is on the top side of the RA axis, pointing at the north pole. After completing your polar alignment, and before starting your star alignment, you need to restore the scope to the Home position. The easiest way to do this is to disengage the clutches on the two axes and manually spin the scope back to the home position. Try to be as accurate as you can. The accuracy of the controller's map of the sky depends on having an accurate home position, because the home position is its reference for the portion of the sky outside of the 3-star alignment triangle.

You can "eyeball" the home position. However, for more accuracy:

  • Rotate the RA axis so the counterweight shaft is horizontal. Measure that it is level using a bubble level. Zero the RA setting circle. Now, rotate the RA axis by exactly 90 degrees (6 hours on the setting circle), so that the counterweight is shaft down. Lock the RA axis.
  • With the scope still not mounted, rotate the Dec axis so the scope would be horizontal if it were mounted. Measure that the dovetail cradle is horizontal by placing a bubble level in it. Set the Dec setting circle to zero.
  • Now rotate the Dec axis so that the scope would be/is pointing at the north celestial pole. Verify on the setting circle that you have rotated it by exactly 90 degrees. Lock the Dec axis.

The mount is now exactly in the Home position. When you balance your scope on the mount, you will move it away from the home position. However, you can restore it to the exact home position you justt measured by using the setting circles. You will need to do so before starting your star alignment.

Remember, any time you disengage one of the clutches, the controller has no knowledge of what you are doing and assumes that the axis has not moved. It loses its reference for that axis. You will need to give it back its reference by performing another star alignment.

When should I mount the scope?

Mounting the scope is problematic because you have to balance it. Balancing requires that you unlock both the RA and Dec axes, potentially losing the accurate home position alignment you have just carefully set up.

If you are able to do the leveling steps described above with the scope mounted, then you can mount and balance the scope before setting up the home position. This depends on having a long enough counterweight shaft or a short enough bubble level that you can apply the level to the shaft with the counterweights in place. It also requires that you use an alternate method of leveling the Dec axis, such as by applying the level to the OTA.

Alternatively, you can mount the scope after completing the home position setup. To do this, do not disturb the setting circles after you have set up the home position. Mount and balance the scope, releasing the clutches as required. Once the scope is mounted, use the setting circles to restore the mount to the home position. Since the home position was established using the setting circles to begin with, you have not lost any accuracy in doing this.

You are now ready to perform your 3-star alignment and begin observing. Clear skies!


The following procedures are not part of the nightly setup.
They are performed one time only when you first set up the scope,
or any time the polar scope has been removed from the mount.


One-Time Setup

Part 1 - Orienting the Polar Scope Reticule

The objective of this procedure is to properly set up the Longitude Index Marker so that it can be used in the Nightly Alignment without Hour Angle procedure above. This procedure only needs to be done once.

You need to calculate a "Longitude Offset" for your specific observing location, to adjust for your location within your time zone. (The manual refers to this by the confusing term "calculated zero position".) By convention, West is negative and East is positive. Multiply your time zone (in hours from GMT) by 15. This is the central meridian of your time zone. For example, Eastern Time Zone is GMT-5, so the central meridian of the Eastern Time Zone is: 15 * (-5) = -75 (75 degrees W). Calculate the difference between your actual longitude, to the nearest degree, and this number. London Ontario is 80 degrees W (-80), so: (-80) - (-75) = -5. London Ontario is therefore 5 degrees west of its central meridian. This number (5 degrees W in this example) is your Longitude Offset, used in step 3 of the Without Hour Angle procedure.

Then continue...


  1. Rotate the mount to orient the image of Polaris in the polar scope reticule at the bottom (6 o’clock) position. Lock the RA axis.

  2. Turn RA Setting Circle to 0. Do not lock it.

  3. Unlock the RA axis. Rotate the mount so the Date Scale / RA Setting Indicator points to 01:30. Use the upper scale in the Northern hemisphere. Lock the RA axis.

  4. Rotate the Date Scale so the Date Scale / RA Setting Indicator is pointing at October 10th.

  5. Using a jeweller’s screwdriver, loosen the set screw on the Index Marker Ring.

  6. Without letting the Date Scale move, rotate the Index Marker Ring to align with the 0 mark on the Longitude Scale. Tighten the set screw on the Index Marker Ring.

    Note that this is the actual “0” mark, not the Longitude Offset (called "calculated zero position" in the manual). You would only use the Longitude Offset in this step if you are using a Polaris transit calculated for your specific location. The transit used in this procedure uses the actual “0” mark1.


Note on Part 1.

1 The date and time (10th of October at 01:30 – [Not 01:00 as stated in the manual] ) used in the procedure are for a known transit of Polaris and for the geographic centre of any time zone. You can substitute the date and time any other known transit of Polaris, but you must then adjust for the location (within the time zone) for which the transit was calculated, and use the correct Longitude Offset in step 6, above.

The geographic correction from the centre of your time zone to your actual observing location is made in step 3 of the Without Hour Angle procedure, where, instead of rotating the Index Marker Ring to align with 0 on the longitude scale, you align it with your Longitude Offset, the number of degrees that the location lies east or west of its time zone geographic centre, using the Longitude Scale.


Part 2: Aligning the Polar Scope Reticule

The polar scope needs to be aligned with the polar axis of your mount. The steps below tell you how to perform this alignment. Note, you can do this procedure at night while pointing at Polaris. However, it is probably easier to do it in the daytime using a distant point as your target (e.g, a street light a couple of hundred yards away). If doing the procedure during the day, you might find it convenient to set your altitude (latitude) to near parallel with the ground to put the eyepiece of the polar scope into a comfortable position. Just be sure to leave room to make vertical adjustments in both directions. Also, do this procedure without an OTA or counterweights. It will make turning the mount a lot simpler.

  1. Locate a distant object and place it under the cross at the centre of the polarscope reticule.
  2. Rotate the mount in RA 180 degrees (i.e., 12 hours on the RA setting circle).
  3. Note the displacement of your target from the centre of the crosshairs. If it is not displaced at all, it means your polar scope reticule is already properly aligned and you don't need to do any more. If it is displaced, continue with the next step of the alignment procedure.

  4. Use the three adjustment screws on the polar scope to move the reticule so that exactly one-half of the displacement is corrected for. For example, if the displacement were about half an inch in the direction of 1 o'clock, then you would adjust the cross at the centre of the reticule to go half the distance in that direction (See Figure h-3}.

  5. Now continue to move the cross using the altitude and azimuth adjusters on the mount. When the target is back under the cross, go back to step 2, but this time rotate the mount 180 degrees in the opposite direction. If you still get displacement of the target, repeat steps 3-5.

You can now proceed to the Nightly Alignment without Hour Angle procedure.