The Morse Equatorial to Altazimuth Transformer Telescope Mount

Mel Bartels, February 2013

Morse's mount deserves wider attention. Here is a representation of his design as described in Scientific American, June, 1942, Ingalls and pictured in Henry Paul's, "Telescopes for Skygazing".

A curved arc in the shape of a sickle attached to a tracking cylinder tracks the telescope's tube across the sky in an equatorial arc. The rear of the telescope's tube is clamped to the sickle by a trolley at the desired Declination. The telescope's tube pulls the altazimuth frame along with itself. The tracking cylinder is polar aligned with the polar axis cutting through the telescope tube's center of gravity. The tracking cyclinder only spins: since it is attached to the ground board it stays motionless while the rocker box rotates around it.

Long before there were computerized altazimuth drive systems for telescope mounts, the Morse mount mechanically translated equatorial motion to altazimuth motion.

As explained in the Scientific American article, the idea originated with A.B. Hendricks Jr of Pittsfield, Mass in 1936. Hendricks' idea was to link equatorial motion to an altazimuth mount. Upon seeing this in 1936, H.F. Morse of Southport, Connecticut devised an entirely different approach to the mechanical transformer.

He wrote that, "The object was to avoid certain inherent shortcoming in large equatorial mountings. Estimates indicate a much lower cost. Materials could be better used-with lessened total weight. Because there would be no transfer of weight from one bearing to another, there would be no distortion of parts. Because of ease and flexibility of the adjustments, less precision work would be required on various details. Astronomers would work in an always level position and in a constant temperature room at either end of the horizontal axis, where light could be directed with three reflections. Because the tube moves about the horizontal axis in one plane alone, the tube could be made very rigid and at the same time relatively light. The whole instrument could be floated in an annular tank of mercury, thus leaving only enough weight on the annular track (precision ground) to insure accurate rotation around the vertical axis."

A curved blade representing the Declination angle is attached to the polar axis drive which represents the hour angle. The telescope's axis below the tube is tied to the curved blade. The altazimuth axes intersect the polar axis. An equatorial tracking movement translates into altazimuth motions.

The Sketchup model can be found at

And we can extend the Morse transformer to eliminate field rotation by using a three axis mount like this, showing one hour tracking. Note how the eyepiece angle is lifted up to follow the equatorial tracking arc as opposed to above where the eyepiece angle stays horizontal.

The Great Paris Exhibition Telescope of 1900 also used an equatorial to altazimuth transformer called a Foucault Siderostat. See Wikipedia's, and Journal of the British Astronomical Association, Vol. 95, NO.3/APR, P. 89, 1985

Conceptually linked is the Earl of Crawford's tracking arm. The length of arm represents the Declination with the arm tying the polar axis to the tube's axis, resulting in an identical equatorial to altaziuth transformation.

Both equatorial axes and both altazimuth axes intersecting is an optimized design. I strongly suspect that the designers started with less optimal designs where the equatorial portion of the transformer was below or at the side of the altazimuth portion. This takes us back into the rich sophisticated world of analog devices and mechanical linkages. It also gives the modern day amateur new design possibilities.

After some thought, mental gymnastics and immersing myself in the mechanical analog world of linkages I devised an equatorial to altazimuth transformer where the equatorial portion is placed at the side of the altazimuth mount. Two disks, one under the altazimuth mount and the other at the bottom of the equatorial section, rotate against each other such that the equatorial portion maintains its polar alignment. The altitude arm is coupled to the curved Declination arm. Just as in the Morse transformer proper, all four axes intersect at one point to the side of the rocker: altitude, azimuth, polar equatorial and Declination. Here I've scaled the polar portion smaller, albeit increasing leverage.

As the equatorial portion tracks, it forces the altazimuth portion to track also. Interestingly, the equatorial portion could be set free to move as needed as the scope is aimed about the sky. This causes the equatorial portion to act as setting circles. In fact, the field rotation angle can be read too.

Here is the change in position after one hour of equatorial tracking. The equatorial portion maintains its polar alignment while the altazimuth portion is forced into tracking an equatorial tracking arc across the sky. This could be extended to a three axis mount if the Declination car is coupled tightly to the altitude extension.

Here's the arc extended into an armillary sphere. Note that the telescope's pointing position has changed: the hour angle is increased, the Declination lowered, the altitude lowered and the azimuth increased.