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Wednesday, December 1, 2010

Cleaning the 40 Inch Mirror of the Wise Observatory Reflector - Part I

Through the kindness of my friend Nachliel who works at Tel Aviv University's Wise Observatory in Mitzpe Ramon, I was given permission to observe and photograph the cleaning of the 40 inch (40") mirror of the Ritchey-Chretien reflector at the observatory last Sunday. While not huge by today's standards, the telescope is still a substantial research instrument and is used in leading edge research such as the search for earth-like exo-planets. It was very exciting to be so close to the big scope and learn the details of what holds it together as it was disassembled to remove the main mirror. It was also a chance to learn the mirror cleaning techniques of Ezra, the observatory's long-time technical director.

The telescope and observatory were inaugurated in 1971. It's first finding was a comet in 1972 that was actually discovered by an Egyptian astronomer since all of the Jewish astronomers had been called up to do battle in the 1972 Yom Kippur War with Egypt!


When I arrived the telescope was in its parked position and Ezra, the technical director, Shai, and students Matan and Yevgeny were preparing to remove the instruments on board the telescope.

The 40" reflector in its parked position. (Click for full size images.)

All of the telescope's motions are now controlled by computer, but in the old days this analogue console was used to operate the telescope and control its tracking of the stars.



Yevgeny at the old analog console.

The first order of business is to remove the digital camera, custom made by the Planck Institute in Germany. The camera and telescope have an actual field of view of 1 square degree, about twice the apparent size of the full moon, which is huge for an instrument this size.

The digital camera is unbolted, lowered, and moved aside.

With permission, I quickly scurry over to the telescope where I snap this self-portrait looking up the open optical tube. My reflection is seen in the hyperbolic secondary at the top, which in turn can be seen reflected in my camera lens.

The winch is made ready to lower the 2 ton mirror to the work floor below the observatory.

The trap door in the observatory floor is removed to give access to the work room about 50 feet below.

After removing the metal plates that hold it to the telescope, the Ritchey-Chretien corrector plate is removed from the bottom of the telescope tube. (Note: A Ritchey-Chretien has no corrector plate, just two hyperbolic mirrors, so I don't know what this plate was for.)

This is one dirty corrector plate. Note all of the dust and the bird feather at 3:30.

The corrector plate is set aside to be cleaned later with the mirror. (Perhaps a field flattener?)

Everyone now turns their hand to removing the heavy metal plates that secure the mirror mount to the telescope tube.

The telescope tube and dome seen through the trap door from the lower work floor.

The dolly for moving the mirror is now raised into position beneath the mirror mount to receive the mirror when the observatory floor is lowered.

The 2 ton mirror is deposited on the dolly and wheeled away from the telescope tube.


Our first sight of the mirror in its cell...and it is extremely dusty!

For those of you afraid of working close-in with metal tools around a mirror, Ezra is seen at the top right using a screw driver to remove one of the three mirror clips holding the mirror to its cell.

Up up and away. The mirror is lifted clear of the cell and swung around to the trap door...

...where it descends into the work area below.

The mirror is deposited into its custom-made plexiglass bathtub.

Elapsed time to this point: Approximately 3 hours.
To be continued. Next post - cleaning the mirror.

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