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An Extraordinary Object

The largest telescope in the world in the 1860s was made in Boston by Alvan Clark & Sons for the University of Mississippi. Clark eventually built five consecutive large refracting telescopes. This magnificent piece, part of the Adler’s collection of scientific instruments, consisting of brass and walnut burl veneer spanning an incredible 22 feet.

The largest telescope in the world in the 1860s was made in Boston by Alvan Clark & Sons for the University of Mississippi. Clark eventually built five consecutive large refracting telescopes. This magnificent piece, part of the Adler’s collection of scientific instruments, consisting of brass and walnut burl veneer spanning an incredible 22 feet.

An Extraordinary Object

The story of the Dearborn Telescope starts with the Civil War. In 1860, Frederick A.P. Barnard, president of the University of Mississippi, wanted to build the world’s largest refracting telescope. Barnard ordered an 18-1/2” lens from the Massachusetts firm of Alvan Clark and Sons, one of the first significant American astronomical instrument makers. 

During testing, the lens was used to identify Sirius B, the first known white dwarf star. But, unfortunately for Ole Miss and Alvan Clark, the Civil War interfered with the transportation of giant telescope lenses and the lens never made it to Mississippi. 

However, the Chicago Astronomical Society (CAS) purchased the impressive lens in 1863 and installed it in a tube – also by Clark – in the Dearborn Observatory at the old University of Chicago (This was not the current University of Chicago, which opened in 1892). It remained the largest refracting telescope in the world until 1868. Today, the largest refracting telescope (40”) is at Yerkes Observatory in Williams Bay, Wisconsin. Alvan Clark and Sons also made the Yerkes lens.

University of Chicago went bankrupt in 1881 and in 1887, CAS agreed to house the telescope at the new Dearborn Observatory on Northwestern University’s campus. By 1911, the lens needed a more modern mounting and in 1929, the original Clark tube and mount were donated to the newly established Adler Planetarium. The lens still remains in use at Northwestern.

For nearly seventy years, the tube and mount were on constant display at Adler. To protect the wood from deterioration, the planetarium covered the 22-foot tube with layers of varnish. This varnish was unstable and began to break down to a darker color, obscuring the original beautiful walnut veneer. By 1997, the telescope was in need of major conservation. 

Contractors do the majority of conservation of the Adler’s collection and the firm selected for the Dearborn specialized in furniture conservation. The team was able to determine the original finish of the tube because the metal parts attached to the tube were not removed when the “protective” varnish was applied. Like what happens when you paint over a screw, some of the original surface was preserved where the metal met the wood. The deteriorating varnish was carefully removed with solvents to once again expose Clark’s original walnut veneer. 

Today you can see the restored Dearborn in the exhibition Telescopes: Through the Looking Glass. The current means for maintaining the telescope involves no public handling, a light-controlled environment, and regular dusting!

Lauren Boegen is the Digital Collections Manager at the Adler Planetarium. 

 

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