Kids Research Express

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, 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 (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, 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...

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 c...

Compression systems employ four elements in the refrigeration cycle: compressor, condenser, expansion valve, and evaporator. In the evaporator the refrigerant is vaporized and heat is absorbed from the material contents or the space being cooled. The vapor next is drawn into a motor-driven compressor and elevated to high pressure , which raises its temperature. The resulting superheated, high-pressure gas is then condensed to liquid in an air- or water-cooled condenser. From the condenser the liquid flows through an expansion valve, in which its pressure and temperature are reduced to the conditions that are maintained in the evaporator.

For every refrigerant there is a specific boiling, or vaporization, temperature associated with each pressure, so that it is only necessary to control the pressure in the evaporator to obtain a desired temperature. A similar pressure-temperature relationship holds in the condenser. One of the most widely used refrigerants for many years has been dichlorodifluoromethane, known popularly as Refrigerant-12. This synthetic chlorofluorocarbon (CFC) when used as a refrigerant would, for example, vaporize at -6.7° C (20° F) in its evaporator under a pressure of 246.2 kPa (35.7 psi), and after compression to 909.2 kPa (131.9 psi) would condense at 37.8° C (100° F) in the condenser. The resulting condensed liquid would then enter the expansion valve to drop to evaporator pressure and repeat the cycle of absorbing heat at low temperature and low pressure and dissipating heat at the much higher condenser pressure and temperature. In small domestic refrigerators used for food storage, the condense...