Kids Research Express

Astrophysics

Astrophysics, the branch of astronomy that seeks to understand the birth, evolution, and end states of celestial objects and systems in terms of the physical laws that govern them. For each object or system under study, astrophysicists observe radiations emitted over the entire electromagnetic spectrum and variations of these emissions over time (see Electromagnetic Radiation; Spectroscopy; Spectrum). This information is then interpreted with the aid of theoretical models. It is the task of such a model to explain the mechanisms by which radiation is generated within or near the object, and how the radiation then escapes. Radiation measurements can be used to estimate the distribution and energy states of the atoms, as well as the kinds of atoms, making up the object. The temperatures and pressures in the object may then be estimated using the laws of thermodynamics.

Steady-State Theory

Steady-State Theory, theory of cosmology, or the study of the universe and its origins, that was once a rival to the big bang theory, which proposes that the universe was created in a giant explosion. The steady-state theory holds that the universe looks, on the whole, the same at all times and places. The Austrian-British astronomer Hermann Bondi and the Austrian-American astronomer Thomas Gold formulated the theory in 1948. The British astronomer Fred Hoyle soon published a different version of the theory based on his mathematical understanding of the problem. Most astronomers believe that astronomical observations contradict the predictions of the steady-state theory and uphold the big bang theory.

Gold, Thomas

Gold, Thomas (1920- ), Austrian-American astronomer, born in Vienna and educated at the University of Cambridge. He is best known as the developer—with Austrian-British mathematician Hermann Bondi and British astronomer Fred Hoyle—of the steady-state theory of the universe. The theory, proposed in 1948, holds that the universe is homogeneous and that matter is continuously being created as the universe expands. Most scientists currently endorse the big-bang theory instead. Gold also developed the accepted explanation of pulsars as being spinning neutron stars.

Spectroscopy

Spectroscopy, in physics and physical chemistry, the study of spectra (see Spectrum). The basis of spectroscopy is that each chemical element has its own characteristic spectrum. This fact was recognized in 1859 by German scientists Gustav Robert Kirchhoff and Robert Wilhelm Bunsen. They developed the prism spectroscope in its modern form and applied it to chemical analysis. One of two principal spectroscope types, this instrument consists of a slit for admitting light from an external source, a group of lenses, a prism, and an eyepiece. Light that is to be analyzed passes through a collimating lens, which makes the light rays parallel, and the prism; then the image of the slit is focused at the eyepiece. One actually sees a series of images of the slit, each a different color, because the light has been separated into its component colors by the prism. The German scientists were the first to recognize that characteristic colors of light, or the spectra, are emitted and absorbed by particular elements.

Refrigeration

Refrigeration, process of lowering the temperature and maintaining it in a given space for the purpose of chilling foods, preserving certain substances, or providing an atmosphere conducive to bodily comfort. Storing perishable foods, furs, pharmaceuticals, or other items under refrigeration is commonly known as cold storage. Such refrigeration checks both bacterial growth and adverse chemical reactions that occur in the normal atmosphere.

The use of natural or manufactured ice for refrigeration was widespread until shortly before World War I, when mechanical or electric refrigerators became available. Ice owes its effectiveness as a cooling agent to the fact that it has a constant fusion temperature of 0° C (32° F). In order to melt, ice must absorb heat amounting to 333.1 kJ/kg (143.3 Btu/lb). Melting ice in the presence of a dissolving salt lowers its melting point by several degrees. Foodstuffs maintained at this temperature or slightly above have an increased storage life. Solid carbon dioxide, known as dry ice, is used also as a refrigerant. Having no liquid phase at normal atmospheric pressure, it sublimes directly from the solid to vapor phase at a temperature of -78.5° C (-109.3° F). Dry ice is effective for maintaining products at low temperatures during the period of sublimation.

In mechanical refrigeration, constant cooling is achieved by the circulation of a refrigerant in a closed system, in which it evaporates to a gas and then condenses back again to a liquid in a continuous cycle. If no leakage occurs, the refrigerant lasts indefinitely throughout the entire life of the system. All that is required to maintain cooling is a constant supply of energy, or power, and a method of dissipating waste heat. The two main types of mechanical refrigeration systems used are the compression system, used in domestic units for large cold-storage applications and for most air conditioning; and the absorption system, now employed largely for heat-operated air-conditioning units but formerly also used for heat-operated domestic units.

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