Telescope

Interrogating the light from stars and the absorption features of atoms and molecules in-between requires some fairly complicated optics in the form of a telescope. However, the telescopes are not restricted to the parts of the electromagnetic spectrum that you can see but use radiation from microwaves to gamma rays to observe the Universe. There is too much to learn about the optics or even adaptive optics of telescopes to be discussed here but there are some properties of telescopes that we must know because they are important for the identification of atoms and molecules. We shall discuss three telescope considerations the atmosphere, the spatial resolution and the spectral resolution. 

Visible UV spanning 300-900 nm contains information on electronic transitions in atoms and molecules. 

Infrared (IR) 1-5 xm and 8-20 xm contains information on vibrational transitions in molecules and functional groups in solids. 

Microwave and millimetre wave 1.3 - 0.35 mm contains information on rotational transitions. 

Radio wave 2-10 m contains information on atomic hyperfine splitting such as the 21-cm line in H atoms. 

Prodded into action by the leaps and bounds of modem technology, the venerable astronomy has rediscovered the enthusiasm of its youth. Today, there is revolution in the air. The exponential growth of astronomical discovery in modern times can be directly correlated with the availability of new detection methods and instrumentation. The science of the sky has become an industry and the great astronomers appear as relics in a landscape completely awash with electronics and data processing. 

From Hipparchos to Tycho Brahe, over almost two thousand years, observation instruments remained practically unchanged - the mural quadrant, the triquetrum and the armillary sphere, heavy wooden or even stone devices the size of a man and often fixed like monuments. Glass and metal would revolutionise astronomy, as would the photographic plate and electronics. 

The solitary astronomer with one eye permanently held against the eyepiece of his or her telescope is an image of the past. Today, we see with computer-regulated instruments, using the new techniques of active or adaptive optics. 

From the beginning of time, humankind could only admire stars similar to our own Sun, neither much hotter, nor much colder. Non-thermal processes based on high-speed particles, totally escaped our gaze and the main aspects of the sky were hidden to us. But today, the solar eye has given way to a new, universal sense of sight. We no longer live in blindness among the sublime realities of the sky. 

One of the great revolutions of the twentieth century was therefore sensory we extended the range of our sense of sight, thus transgressing a morphological dictate. No vision is now excluded. Humanity has finally removed its blinkers. 

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High angular resolution studies with modem THz telescopes and interferometric arrays can even probe the... 

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. 

Figure 4.16 Schematic illustration showing how an experimental plot of modulus against log t (a) can be telescoped (b) by shifting successvie segments by an amount designated as log a.

Since 1963 spectra of many molecules have been detected, mainly in emission but some in absorption. Telescopes have been constructed with more accurately engineered paraboloids in order to extend observations into the microwave and millimetre wave regions. 

The first polyatomic molecule was detected in 1968 with use of a telescope having a dish 6.3 m in diameter at Hat Creek, California, USA, designed to operate in the millimetre wave region. Emission lines were found in the 1.25 cm wavelength region due to NH3. The transitions are not rotational but are between the very closely spaced 2 = 0 and 2 = 1 levels of the inversion vibration V2 (see Section 6.2.5.4). 

Figure 9.34 A LIDAR device using a Cassagrain telescope...

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

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. 

The value of the beam divergence angle given by equation 3 corresponds to that emerging from the laser. The beam may be collimated further by a telescope. The improvement of the coUimation is the inverse of the magnification of the telescope ... 

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