Horse soap shines giant mirror

20 Jun 2002

Optical technicians discover that the best way to clean a giant telescope mirror is to use horse shampoo and a sponge.

How should a giant telescope mirror be cleaned? According to optical technicians at Hawaii's Gemini North telescope, the surprising answer is with horse shampoo and a sponge.

Horse soap

Engineers working on the 8 m diameter, aluminium-coated glass mirror, which is mounted on top of the 4000 m-high peak of Mauna Kea, say that the apparently low-tech solution is the best they've found.

Optical technician Clayton Ah Hee, who supervised the mirror wash, said: "We've found the combination of natural sponges and horse soap to be the most efficient way to get the mirror surface completely clean."

He explained that despite being a strong detergent, horse shampoo is non-abrasive. After removing the accumulated contaminants, it leaves the 24 ton, 20 cm thick mirror free of any residue.

"I know [horse shampoo] sounds kind of simple, but sometimes the simplest solutions are best, even with something as leading-edge as the Gemini telescopes. And the horse soap really works," added Ah Hee.

Periodic cleaning of the mirror involves dismounting it from the telescope, before lowering it five stories onto a washing frame. A crew of more than 20 engineers and technicians are needed for the procedure, which involves more than 500 individual steps.

Along with its identical twin Gemini South in Chile, the Gemini North telescope can provide full coverage of both hemispheres of the sky. Each is fitted with adaptive optics systems, and astronomers recently used Gemini North to image the closest separation distance ever observed between a brown dwarf and a low-mass star.

Author
Michael Hatcher is technology editor of Opto and Laser Europe magazine.