spectral class, in astronomy, a classification of the stars by their spectrum and luminosity. In 1885, E. C. Pickering began the first extensive attempt to classify the stars spectroscopically. This work culminated in the publication of the Henry Draper Catalogue (1924), which lists the spectral classes of 255,000 stars. The stars are divided into 7 classes designated by the letters O, B, A, F, G, K, and M; the hottest stars (O and B) are blue-white in color, while the coolest (M) are red. Each of the letter classes has subdivisions indicated by numerals 0 through 9. Thus, a B0 is the hottest B-type star, B5 is halfway between types B and A, and B9 is only slightly hotter than type A. The table entitled Spectral Classes for Main Sequence Stars gives the characteristics of the seven principal types. To the seven main groups, four more groups have since been added. R, N, and S are classes similar to the K and M types but denote somewhat different spectral characteristics; W indicates a Wolf-Rayet star, the hottest type of star that shines with a steady light. According to a system introduced by W. W. Morgan and others, a Roman numeral is added to the spectral class to specify the luminosity, or intrinsic intensity, of a star. A bright supergiant is Ia, a faint supergiant is Ib, a bright giant is II, a normal giant is III, a subgiant is IV, and a normal dwarf or main-sequence star is V. For example, Sirius is classed as A1 V, a main-sequence white star. Betelgeuse, M2 Ia, is a bright red supergiant. See also Hertzsprung-Russell diagram.

middle class: see bourgeoisie.

class action, in law, a device that permits one or more persons to sue or be sued as representative of a large group of people interested in the matter at issue. The court in whose jurisdiction a suit is brought typically has wide discretion in determining that a class will be so represented. Certain requirements must be met, e.g., the class must be so large or dispersed that actual joinder of all individuals would be impractical; there must be questions of law and fact common to all members, and these must outweigh any individual questions; and the named parties must adequately represent the interests of their class. Certain forms of notice to members of the class, e.g., by newspaper or broadcast publication or by mail, are also required. In most types of suit, all members of the class are bound by the decision, unless a member of the class opted out of the action at the beginning of the lawsuit. An absentee member may be able to contest the outcome on the basis that due process of law was not adhered to.

In the United States, federal and most state courts allow class action suits. Such suits have figured prominently in civil-rights litigation and in other cases brought to further social and economic reform. In recent decades they have been employed notably by groups of consumers and others seeking to affix liability for harm caused by various products, especially through manufacturers' negligence. Major litigation against the producers of the Dalkon shield (an intrauterine device; see birth control), of Agent Orange (a herbicide used as a defoliant in the Vietnam War), and of asbestos insulation has involved class action suits.

Since the 1980s such suits have been under attack, along with negligence litigation in general, with opponents, mainly conservatives and business interests, arguing that many lawsuits are frivolous and that awards are out of proportion to the offense in some juridictions. A study published in 2004 that reviewed several hundred state and federal class action lawsuits from 1993 to 2002 found that, adjusted for inflation, the average annual award in such suits varied but did not progressively increase, while the median award was relatively constant. At the same time, however, federal court data showed that the number of class action lawsuits doubled from 1997 to 2002.

class, in taxonomy: see classification.

Group of people within a society who possess the same socioeconomic status. The term was first widely used in the early 19th century, following the industrial and political revolutions of the late 18th century. The most influential early theory of class was that of Karl Marx, who focused on how one class controls and directs the process of production while other classes are the direct producers and the providers of services to the dominant class. The relations between the classes were thus seen as antagonistic. Max Weber emphasized the importance of political power and social status or prestige in maintaining class distinctions. Despite controversies over the theory of class, there is general agreement on the characteristics of the classes in modern capitalist societies. In many cases the upper class has been distinguished by the possession of largely inherited wealth, while the working class has consisted mostly of manual labourers and semiskilled or unskilled workers, often in service industries, who earn moderate or low wages and have little access to inherited wealth. The middle class includes the middle and upper levels of clerical workers, those engaged in technical and professional occupations, supervisors and managers, and such self-employed workers as small-scale shopkeepers, businesspeople, and farmers. There is also often an urban substratum of permanently jobless and underemployed workers termed the “underclass.” Seealso bourgeoisie.

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