Telescope mirrors

These alloys are of vital importance in the construction of modern aircraft and rockets. Aluminum, evaporated in a vacuum, forms a highly reflective coating for both visible light and radiant heat. These coatings soon form a thin layer of the protective oxide and do not deteriorate as do silver coatings. They are used to coat telescope mirrors and to make decorative paper, packages, toys. 

Schott Zerodur P-quart2 soHd solution, Si02 2ero expansion electric range tops, telescope mirrors... 

Thermal Properties. Many commercial glass-ceramics have capitalized on thek superior thermal properties, particularly low or zero thermal expansion coupled with high thermal stabiUty and thermal shock resistance properties that are not readily achievable in glasses or ceramics. Linear thermal expansion coefficients ranging from —60 to 200 x 10 j° C can be obtained. Near-zero expansion materials are used in apphcations such as telescope mirror blanks, cookware, and stove cooktops, while high expansion frits are used for sealing metals. 

Sputtered silver mirrors are used for solar energy (qv) collectors and astronomical telescope mirrors. Approximately 3 t/yr of silver are used in the United States for low emissivity windows. 

Fig. 7.2. The elastic deflection of a telescope mirror, shown for simplicity as a flat-faced disc, under its own weight.

It is reasonable that the resulting deflections will be a function of the location of the support points and the force applied at these supports. The support point locations and forces can be adjusted in order to minimize the rms gravity induced deflections. When this is done, the rms deflections can be written as (see Telescope Mirror Supports, Nelson et al., 1982)... 

Telescope Mirror Supports Plate Deflections on Point Supports. Nelson, J., Lubliner, J. and Mast, T, 1982, SPIE. 332, 212... 

Deformable mirrors are usually placed at a greatly reduced image of the telescope entrance pupil - the typical diameter of PZT or PMN based deformable mirrors is in the range 10-20 cm. A completely different approach is to make one of the telescope mirrors deformable, and the best choice is the secondary mirror (relatively small and usually coincides with the aperture stop for in-... 

Telescope mirrors are silvered by prepg a soln of K hydroxide and Ag nitrate ammonia and covering the mirror with it. Unless the prepn steps ace followed carefully, SF may form which is very expl. Fof this reason the USBurStds recommends that goggles be worn to avoid an unnecessary risk. The risk is especially great if the "silvering" soln is kept for more than several hours. 

Li20-Si02 (LAS). The trade names of such glass-ceramic matrix materials are Corningware, Zerodur and Ceran. This type of glass-ceramic matrix material has nearly zero thermal expansion and high thermal shock resistance. It is used for the production of optical and telescopic mirrors. 

AMATEUR ASTRONOMER S HANDBOOK. J.B. Sidgwick. Timeless, comprehensive coverage of telescopes, mirrors, lenses, mountings, telescope drives, micrometers, spectroscopes, more. 189 illustrations. 576pp. 5K 8V. 

The metal is reactive, and when strongly heated it burns rapidly in air or oxygen. Aluminum dust forms an explosive mixture with air. Under ordinary conditions, however, aluminum rapidly becomes coated with a thin, tough layer of aluminum oxide, which protects it against further corrosion. This protection is so effective that the sixty-inch and hundred-inch telescope mirrors on Mount Wilson have not... 

Telescopic Mirror-ecale Method, Adjustments, and Tests.. Large Svo... 

Cerium oxide is also used as an abrasive. An abrasive is a powdery material used to grind or polish other materials. Cerium oxide has replaced an older abrasive known as rouge for polishing specialized glass, such as telescope mirrors. 

Many aluminosilicate glass ceramics are based on framework structures of AIO4 tetrahedra, which, when crystallized, posseses low thermal expansions. This gives the glass ceramics based on them near zero expansions and thus excellent dimensional stability, thermal shock resistance, and mechanical strength. Aluminosilicate glass ceramics are used commercially as telescope mirrors, thermally stable structures for satellites and space probes, gyroscope components, heat-resistant windows, stove tops, and cookware. 

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