Did you know...
... that "Brille", the German word for eyeglasses, comes from beryl, the name of a transparent crystal?
It seems that eyeglasses are an invention of the Middle Ages. At that time, however, glasses were not made of glass, but from a mineral which comes in a clear, transparent crystalline variety. This material, beryl, was the material the first lenses were carved from.
Cardinal Hugh of St. Cher wearing glasses made of beryl to help his eyesight. This fresco in a church in Treviso, painted in 1352 by Tommaso da Modena, is the oldest known pictorial representation of eyeglasses. (Source: Books, Banks, Buttons: And Other Inventions From The Middle Ages)
Beryl is, chemically speaking, a cyclosilicate, a compound of the light metals beryllium and aluminium with silicon and oxygen. Its chemical formula is Be3Al2(SiO3)6. In its pure form, beryl is a colourless, clear mineral, but if it is "doped" with trace amounts of other metals, it can have all kinds of colours - and be very precious. Emerald, for example, is a variety of beryl, coloured green by impurities of chromium and, sometimes, iron.
Now, colour centres are a very interesting physics topic of their own, but I was reminded of this beryl story when I came across a comprehensive, freely available paper on the James Webb Space Telescope.
The JWST is a planned satellite telescope which is sometimes called the successor of the Hubble telescope. One of its scopes is to study the first galaxies in the young Universe at a redshift in the range of 5-10. This means that all visible light is shifted far into the infrared. So, the JWST is optimised for observations at the infrared part of the spectrum. It will have a primary mirror with a diameter of 6.5 meters (21 feet 4 inches) which consists of several segments. And these segments will be made of - beryllium.
The primary mirror of the James Webb Space Telescope will consist of 18 honeycomb-shaped segments made of beryllium (Source: NASA)
Metallic beryllium was chosen to produce the mirror because its stiff, light weight, has very small thermal expansion over a wide temperature range and holds its shape at the low 50 Kelvin at which the telescope will operate.
It's a funny coincidence that the same element, which as a main component in a mineral was used to produce the first eyeglasses, will soon help us to look back into the youth of our Universe!
TAGS: PHYSICS, SCIENCE, JAMES WEBB SPACE TELESCOPE