The Easy Way by John Reagan

Getting your platform aligned can take hours following the "normal methods" of equatorial alignment. This procedure is very useful during the building of an equatorial platform since no drive is required.   You can check to see how your bearings are rotating long before you complete the drive.  Pushing the platform by hand is all that is needed.  It is also very useful for those of us that do not have east west views and have difficulty using the 2 star drift method when drive errors are present.   Here is how to do it in a snap using no tools other than your finder scope already mounted on your DOB:

First Time - One Time Only:


41 degrees North




To Pole


1.  With your DOB flat on the ground, mark your latitude on the altitude bearing using a protractor (picture - upper left).  Don't worry too much about accuracy it is just for a quick reference (My Connecticut location is 41 degrees north latitude).
2. Mount your DOB on the platform. 
3. Find the south center of your rocker box and mark it (picture - upper right).    Align the mark with the center of your south bearing on the platform. 

Alignment Procedure:

1.  Level the platform groundboard and platform base.
2.  Point the platform at the Pole Star.
3.  Move your scope so the altitude is adjusted to you latitude mark.  Rotate the scope so the south mark lines-up on the rocker box.  Your scope should be pointing pretty close to the Pole Star.
4. Raise or the lower the north side, or the south side, of the platform to get the Pole Star in the finder.  Twist the platform groundboard east or west to get the Pole Star in the finder. With the star centered and both marks lined up on the scope, you are getting very close.
5.  Rewind the platform.  Watch the Pole Star in your finder scope and fast-forward the platform to the max position. You don't have to wait for the earth to rotate to tell how far off you will be in one hour of tracking.
6. If the star moves left or right (real world) adjust the platform up or down (adjust the north side up or down or the south side).  I am not giving actual directions for the corrections because of the difficulty translating directions for the different types of finder scopes.  Just move the platform and repeat step 5.  Did it get better or worse?  Go the opposite way if it got worse.  Keep rewinding the platform and making adjustments until the Pole Star stays centered, or wanders back and forth in the finder.
7.  If the star moves up or down (real world) twist the platform groundboard east or west.  Keep rewinding and watching to see if you get better or worst.  Continue until the Pole Star stays centered, or wanders back and forth across the center of the finder.
8.  For really fine work, use the DOB to view the Pole Star. All movement in the position of the Pole Star caused by polar alignment will be smooth motion. If the Pole Star drifts in erratic motion, or oscillates, there is a problem in the platform (bearing smoothness, misaligned bearing centers, moving bearing center, or incorrect geometry). If you can get the Pole Star to drift back and forth in your finder as you rotate, there in NO reason to ever do a 2 start drift method. Your platform is aligned to within your platforms tracking ability.





This method works better than the two star drift method for me, and it is much quicker. The tracking rate accuracy is removed from the alignment procedure - a problem for DC motor driven tangent drives.


The basic procedure is complete.



The discussion below will help you get aligned quicker if you have an upright correct image finder.


The description below details the motion seen in an upright correct image finder.  A finder can be upright and reversed L/R.  It can also be both upside down and reversed.  Check by looking at a land object.  Trying to perform this test without a correct upright finder will likely drive you crazy.

      Virtual Cone of the Platform

The goal is to get the Pole Star to be in the center of the platform's rotation.  The picture above shows the finder scope pointing at the Pole Star and the platform center pointing at the Pole Star.  If the platform rotates 15 degrees, the finder will rotate around the center of the platform's center and the Pole Star will not move in the finder.


     Virtual Cone of the Platform


In this example of a misaligned platform (above), the platform is pointing east of the Pole Star.  The platform is perfect in the north / south alignment.  Without moving the platform, the scope is pointed at the Pole Star and centered in the finder scope.  We can never really see where the platform center is pointing, so we have to watch what happens to the Pole Star when the platform is rotated. 


15-degrees rotation of the platform and the finder



Rotation of the platform (above) will cause the finder to rotate while the Pole Star does not move. We humans tend to see the change in the Pole Star position in the finder as the star moving up in the finder.  We do this because out there in the dark, there is no frame of reference.

If the platform moves 15-degrees, then the finder rotates 15-degrees, the north Pole Star appears to move in a 15-degree arc.  The star appears to move to the top of the finder.  So a platform that is east of the north Pole Star, the Pole Star appears to rise in the finder during rotation.  Remember, it is the finder that moved, not the star or the platform's center axis (hopefully the platform's axis just rotates):
1) platform east of the Pole Star, the star appears to rise
2) platform west of the Pole Star, start appears to sink
3) platform north of Pole Star, star appears to move left
4) platform south of Pole Star, star appears to move right

Visualize the finder scope with the star centered in all 4 positions and rotate the platform. It will help you save time during alignment.  Once you have the finder scope rotating in your mind, picture that "the star always gets left behind".


To all the Southern Hemisphere Folks,


I am sorry for the North Latitude bias.


John Reagan


Hosting by WebRing.