dome

For a telescope with an altazimuth mounting the rotation rates of dome and telescope are the same. The dome needs only to be slightly larger than the telescope, and can be square or oblong. The cost of the dome is thus greatly reduced.

Turkish dome

a covering of buildings and structures, serving as a roof over spaces, normally those with a circular, polygonal, or elliptical floor plan. The shape of the dome follows a curve that is convex to the exterior of the building. Stresses existing in a dome consist not only of the basic compression loads, which transmit the weight of the roof to the supports, but also of horizontal thrusts. To accommodate the horizontal forces, special tension structures are sometimes provided, such as support rings at the base of the dome. Such structures were first introduced in the 15th century.

It is possible that the first domes were parts of thatched huts made of pliable material (reeds, branches) and clay. In antiquity, domes were built of stone and fired brick. These domes were actually corbel vaults with horizontal circles of masonry that progressively diminished in diameter in such a way that no horizontal thrust was transmitted to the walls (buildings in the town of Eshnunna in Mesopotamia, dating back to the early third millennium B.C.; the Treasury of Atreus in Mycenae, 14th century B.C. [?]). Corbel vaults were widely used in the popular architecture of many countries, for example, the gvirgvini, the stepped roof of Georgian folk dwellings.

In ancient Rome the true dome attained great importance after the introduction of squinches and particularly after the invention of concrete. In centrally planned buildings, domes with large spans enhanced the role of the covered spaces within the architectural composition and imparted to them spaciousness and solemn grandeur. The power and firmness of religious beliefs often found expression in such architecture (for example, the imposing dome of the Pantheon in Rome).

In Byzantine architecture, pendentive domes and squinch domes were widely used. (Both had appeared earlier in the architecture of ancient Rome and of Iran during the age of the Sassa-nids.) Squinches and pendentives made it possible to erect a dome above a space with any type of floor plan (for example, Hagia Sophia in Constantinople). During the Middle Ages various types of domes were used in Europe and the Caucasus, predominantly in cruciform domed churches (for instance, Dzhvari Church near Mtskheta in Georgia; Ripsime Church in Echmiadzin in Armenia). In the feudal states of Middle Asia and the Middle East, buildings appeared with large central domes.

As the role of the dome became understood in terms of its effect not only on the interior but also on the exterior of the building, the outer contour of the dome changed in its relation to the inner contour. Later the false dome appeared—an external shell with an outline differing from that of the dome proper. Such a shell usually consisted of curvilinear roofing supported by wooden rafters; an early example is the dome of St. Mark’s Church in Venice (ninth to 11th centuries). Domes with outer shells, which usually crowned the vertical space of religious buildings and were calculated to be in harmony with their architectural or natural surroundings, were particularly popular in the architecture of medieval Russia and of Middle Asia (for example, the mosque of Bibi Khanum in Samarkand, 1399–1401, which has an inner and an outer dome).

During the Renaissance the treatment of the dome as a plastic shape in space and as a dominant feature of urban design became widespread in the architecture of Western Europe. An example is the dome of Santa Maria del Fiore in Florence (1420–36, architect F. Brunelleschi), where for the first time the two shells of the dome were connected by stiffening stone ribs and by wooden rings, thus forming a unified structure.

Beginning at the end of the 18th century, domes were used in secular buildings. In the second half of the 19th century, domes of stone and brick were replaced by domes constructed of glass and metal frames or of wood or reinforced concrete. Masonry domes were at a disadvantage because of their great weight and the large amount of labor required for their construction. In the 20th century, with the development of monolithic and precast reinforced concrete, thin-walled shell vaults, and metal structures, the diversity of domical shapes and structures increased drastically. New types that appeared included ribbed domes, rib-and-ring domes, domes with rippled inner surfaces, geodesic domes (designed by B. Fuller, with diameters up to 150 m), and prefabricated domes creating the impression of a monolithic whole (designed by P. L. Nervi). Other innovative types include domes built of polymeric materials and those with an inflated double shell.

(geology), mode of occurrence of rock. (1) Volcanic (or magmatic) dome, a mode of occurrence of igneous rock in the form of a bun-shaped body. It forms on the earth’s surface when very viscous acid lava is extruded from a volcanic vent. It often has a characteristic radial and concentric jointing.

(2) Granite-gneiss (or gneiss) dome, an uplift of layers of the earth’s crust; the central part of the uplift is composed of granite-gneisses and gneisses, sometimes cut by granites, occurring in relatively gently sloping beds. The periphery of the gneiss core is composed of crystalline schists of increasingly lower degrees of metamorphism, crushed into small folds that are often tilted toward the center of the dome. Granite-gneiss domes form as a result of the floating up of granite material during regional metamorphism and granitization or repeated heating of the ancient granite-gneiss base. These domes are found mainly in the shields of ancient platforms. They may be many dozens of kilometers in diameter.

(3) Tectonic dome, a more or less rounded uplift of layers of the earth’s crust, which slopes down in all directions from the center of the dome. They may be dozens of kilometers (and sometimes up to 100) in diameter. Tectonic domes are found on platforms for the most part.

(4) Salt dome, a rounded uplift of rock layers with a nucleus of rock salt or other kind of salt. It forms when, owing to its lower density and high plasticity as compared to other sedimentary rocks, salt rises and is intruded. These domes are common in areas of deep submersion of the crystalline crust in platform basins and in the foredeeps and intermontane areas of mountain belts. In the USSR they are found in the Caspian, Dnieper, Donets, Tadzhik, and other basins.