30 ASTRONOMY • MARCH 2020

How the Ritchey-Chrét

J

ust over 100 years ago, on October 31,

1919, George Willis Ritchey was fired

from the Mount Wilson Observatory and

ostracized by the American astronomical

community. This dramatic event would

ultimately set back by 50 years the devel-

opment of the Ritchey-Chrétien telescope

— the advanced optical system used in

today’s best research telescopes.

A fastidious man

Ritchey, the son and grandson of Irish immigrant

furniture makers, had been trained in the art and

craft of fine furniture design and construction. But he

later discovered a love of optics — especially telescope

optics — instrument design, and astrophotography.

By the early 1900s, Ritchey had established himself as

one of the world’s leaders in shaping, polishing, and

testing optics for use in telescopes.

Meticulous and methodical to a fault, Ritchey was

also imperious and demanding of his shop assistants.

He was one of the first to introduce standards for

shop protocols: varnishing the walls and ceilings,

keeping the f loor wet during polishing, double sealing

windows, and using air filtration systems to help

eliminate dust. He developed most of the techniques

he used for polishing and testing mirrors through

years of careful work and detailed note-taking. His

1904 paper for the Smithsonian Institution, “On the

Modern Ref lecting Telescope, and the Making and

Testing of Optical Mirrors,” had become a must-read

for any aspiring telescope optician. In it, Ritchey

detailed the process by which he shaped a glass disk

into a perfect section of a sphere and set about creat-

ing the curved shape for the mirror.

One of those inspired by Ritchey’s writing was

Henri Chrétien — a French astronomer, physicist,

and optical engineer. Chrétien came to Mount Wilson

as a visiting researcher from the Nice Observatory in

France in 1909. There he met Ritchey, and the two

George Ritchey and
Henri Chrétien appear
amidst the delegates to
the Fourth Conference
of the International
Union for Cooperation
in Solar Research at
the Mount Wilson
Observatory in 1910.
MOUNT WILSON AND PALOMAR
OBSERVATORIES, COURTESY OF AIP
EMILIO SEGRÈ VISUAL ARCHIVES