Article I wrote about the First German Equitorial Mount for a Telescope

The story of Joseph von Fraunhofer and the first GEM (German Equatorial Mount)

Little do we generally appreciate the heritage of the modern telescope technology we use today. But over the centuries the designs have made a steady advance from Hans Lipperhey’s “instrument for seeing far” to Galileo’s crude “telescopium” all of the way to the latest computer driven models that we use today.

But do you know who made the most fundamental and important advance in telescope mountings in history? It was Joseph von Fraunhofer, who despite a suffering a terrible accident in childhood and a short adult life made an impact that reverberates in amateur astronomy to this very day.

Fortunately his accident opened his future. While working as an apprentice ornamental glass cutter and mirror maker in conditions of near slavery, the house of his master collapsed. The accident killed the master’s wife, but the young man was pulled from the wreckage. A well heeled Munich entrepreneur and lawyer named Joseph von Utzscneider witnessed the rescue and took him under his wing, providing him with books on physics and mathematics. Although Fraunhofer still had to work as an apprentice for the glasscutter, he self-educated himself in optical theory and soon became quite skilled. After King Max gave him a present of eighteen ducats, he was able to purchase his way out of his apprenticeship. Then he was hired by Utzscneider’s Institute to take advantage of his talents at the young age of 19.

Utzscneider ordered his employee Pierre Guinard to instruct him. Lessons were taught in glass manufacture, lens grinding and even mechanical engineering. But soon the young upstart recognized flaws in his teacher’s production methods, and this eventually caused friction between them. Guinard finally left the plant for France in 1814, and by that time Fraunhofer was fully trained in the art of optical glass making.

He then continued his optical studies, working on innovative designs for eyepiece lenses and objectives. He also delved into the study of the nature of light itself. His objective lens sizes steadily grew and took advantage of the advances in glass materials of the time. His big project came when a 9.5 inch objective lens and telescope was ordered from the Dorpat Observatory in Russia (now Tartouo, Estonia) in 1819.

At the time, the new refractor telescope was the world’s largest. Its 14-foot long tube of wood was attached to a revolutionary mount that made observation a much easier task. We know it today as the German Equatorial Mount (GEM). Before then, telescopes were mounted on simple altazimuth tripod mounts or unusual box frame mounts, or simply propped up against walls. These crude mounts made observation very difficult as any vibrations were magnified in the eyepiece.

The brass right ascension drive that was built made the telescope the first in the world to automatically track objects in the sky as the earth turns. Driven by clock weights that were set prior to the observing run, the drive was adjusted and set to keep the objects centered in the eyepiece for uninterrupted study. However, the RA drive lacked rigidity because the drive gear itself was too small – making the mount wobble. This is an engineering and cost tradeoff that is made in the lower end GEM designs to this day.

The declination axis was locked for slow motion adjustments by a long and inconvenient handle, so in most cases it was left unclamped – making it hard to set.

Even with these limitations, staff astronomer F.G. Wilhelm Struve used this instrument to measure over 3,000 double stars with precision of less than one arc second. He was actually impressed with the telescope:

“…undetermined which to admire most, the beauty and elegance of the workmanship in its most minute parts, the propriety of its construction, the ingenious method of moving it, or the incomparable optical power of the telescope, and the precision with which objects are defined.”

One wonders about the disparity between the quoted praise versus the design deficiencies, but this is likely due to the fact that this was the first GEM ever built.

Fraunhofer went on to build other telescopes but succumbed to tuberculosis at the age of 39 on June 7, 1826. He pioneered a generation of fine German telescope engineering, and as a pioneer in the field of astrophysics he was the discoverer of the absorption lines in the solar spectrum. These are now known today as Fraunhofer lines his honor. These spectral lines are the fundamental tools in astrophysics and astronomy today.

Fortunately, the original Dorpat refractor telescope and mount still exists. It can be seen today at the Tartouo Observatory. Carefully restored in 1993 under the directorship of Enno Ruusalepp, it sits on its original sturdy wood mounting and is quite elegant in appearance.

So the next time you set up your German Equitorial mount, think of this brilliant eighteenth century German engineer and the pioneering work that he did.

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~ by matthewota on April 21, 2008.

One Response to “Article I wrote about the First German Equitorial Mount for a Telescope”

  1. Nice article, R. Schievink (Germany).

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