ORLOV, SERGEY VLADIMIROVICH

(b. Moscow, Russia, 18 August 1880;d. Moscow, 12 January 1958)

astronomy, astrophysics.

Orlov was the son of a physician. After graduating in 1899 from the First Gymnasium in Moscow, he entered the department of physics and mathematics of Moscow University. Orlov began his scientific career while a student, when, influenced by the university’s observatory and conducted observations with the transit instrument. Following graduation in 1904, Orlov continued to work in the observatory, began teaching, and served as an artillery officer in the Russo-Japanese War. Since his former position in the Moscow University observatory was filled, from 1906 to 1918 Orlov taught at the First Gymnasium and began his Study of comets. During 1914–1917 Orlov again was on active duty in the army. After recovering from a compound fracture of the leg, he was demobilized in 1917 and returned to the Gymnasium, where he taught mathematics and physics and served as vice-director until 1920, meanwhile continuing his study of comets. In 1917 he had received the right to teach at the university level; and in 1920–1922 he was professor at Perm University, where he headed the department of astronomy and physics.

In 1922 Orlov was again Moscow, where he became a staff member of the State Astrophysical Institute (acting director 1923–1931) and at the Moscow University Astronomical-Geodesical Scientific Research Institute, which in 1931, after merging with the university observatory, became the P. K. Sternberg Astronomical Institute. From 1931 to 1935 Orlov was its vice-director and from 1943 to 1952 its director.

In 1926 Orlov became professor at Moscow University, Where he gave courses in astrophysics and comet astronomy; in 1935 he received the doctorate in physical and mathematical sciences, and from 1938 he was head of the department of comet astronomy. From 1935 to 1957 he was president of the Commission on Comets and Meteors of the Astronomical Council of the USSR Academy of Sciences. In 1943 Orlov was elected associate member of the Academy of Sciences and was awarded the state prize for scientific work on comet and meteor astronomy. His other honors include two Orders of Lenin, two Orders of the Red Banner of Labot, and several state medals. As early as 1908 he had Photographed and studied photographs of Morehouse’ comet, and in 1910 he had observed Halley’s comet. This work formed the beginning of investigations that led to more than seventy publications on the astronomy of comets.

Bredikhin’s research in the mechanical theory of comet forms was further developed by Orlov and his school. Orlov faced the problem of creating a theory that would embrace the mechanistic properties of motion, as well as the physical peculiarities of comets and their changes through time. At first he examined the mechanistic theory and put its formulas into a form more convenient for calculation. He then gave an improved method of determining the values of the repulsive accelerations of the action of the sun on the particles of comets’ tails; these accelerations were multiples of 22.3 (I + M = 22.3 · n, where n can take a value from 1 to 9). This method was based on careful study of the displacements of separate details of the tails as functions of time.

Enlarging on Bredikhin’s ideas, Orlov examined and returned to the improvement of Bredikhin’s classification of comet forms and developed his own classification of the forms of comet heads. In connection with the latter he produced a theory of the head of the comet, based on the proposition that both the sun and the nucleus of the comet are centers of repulsion forces acting on molecules that separate from the body of the comet’s nucleus as the comet approaches the sun and are pushed out into the tail. According to this theory, cross sections of the nuclei of comets were on the order of several kilometers, a dimension confirmed by further research. This theory was also proved by analysis of the structure of the envelopes of comet heads and calculation of the masses of comets.

While continuing Bredikhin’s work Orlov also pioneered in the astrophysical study of comets, taking into consideration the mechanism of luminescence of a comet and variations in its spectra. He repeatedly returned to the study of cometary luminescence and the laws of its variation in a periodic comet from one appearance to another. Orlov provided a method of determining the parameters of comet’s light and for many comets established the integral, or absolute stellar, magnitudes (the stellar magnitudes reduced to so-called standard conditions, for which one takes the distance of the comet from the sun and its distance from the earth as equal to astronomical unity). As Orlov showed, the law of variation of the parameters of a comet’s light is of great importance for the study of the origin and evolution of comets. In particular he noted that a comet’s brightness, related to standard conditions, depends on the phase of solar activity.

Orlov’s cosmogonic hypothesis suggested that the formation of comets was a result of accidental collisions between two asteroids, which led to explosions that destroyed these small bodies. Fragments acquired varied orbits, usually elliptical. As they approached the sun and came under the influence of its radiation, the fragments released gases that later formed the envelopes of the heads and of the tails of comets. Research on spectra enabled Orlov to determine the gas composition of the straight-tail (type I) comets; less was known at that time about tails of types II and III—he took them to be dust. He was the first to identify lines of nickel in the spectrum of comets.

Orlov’s construction of new astronomical instruments was related to the organization of observations of comets and meteors in the Soviet Union. He created a special camera for photographing comets and developed a method for their photogrammetry. Orlov was widely known as an excellent lecturer.

BIBLIOGRAPHY

I. Original Works. Orlov’s writings include “Issledovanie ochertany golovy komety” (“Research on Outlining the Head of a Comet”), in Zhurnal fizikomatematicheskogo obshchestva pri Permskom Gosudarstvennom Universitete (1919), no. 2, 139–144; “Opredelenie ottalkiva-telnykh sil Solntsa v khvoste komety po dvum nablyudeniam polozhenia oblachnogo obrazounia” (“Determination of the Repulsive Force of the Sun on the Tail of a Comet From Two Observations of the Position of the Cloud Formation”), in Trudy Glavnoi rossüskoi astrofizicheskoi observatorii,1 (1922), 231–236; “O svyazi mezhdu yarkostyu komet i deyatelnostyu na poverkhnosti Solntsa” (“On the Relations Between the Brightness of Comets and Activity on the Solar Surface”), ibid., 2 (1923), 150; “Opredelenie ottalkivatelnykh sil Solntsa-kometa Galleya (1910 II)” (“Determination of the Repulsive Forces of the Sun and Halley’s Comet...”), in Russkii astronomicheskii zhurnal 2, no. 3 (1925), 4–21; “The Series of Carbon Monoxide in the Spectrum of Comets. 1908 III (Morehouse),” in Astronomische Nachrichten, 225 (1925), 397–400; “The Spectrum of the Comet 1882 II” in Russkii astronomicheskii zhurnal,4, no. 1 (1927), 1–9; and “Oblachnye obrazovania v khvoste komety 1908 III (Morehouse), 14–17 oktyabrya” (“Cloud Formations in the Tail of Comet 1908 III [Morehouse] 14–17 October”), in Astronomicheskii zhurnal, 5, no, 4 (1928), 193–202.

Other works are “Mekhstnicheskaya teoria kometnykh form” (“Mechanical Theory of Comet Forms”), in Trudy Gosudarstvennogo astrofizieheskogo instituta,3, no. 4 (1928), 3–79, also in Astronomischeskii zhurnal,6, no. 2 (1929), 180–186; “Priroda ottalkivatelnykh sil Solntsa v khvostakh komet” (“The Nature of the Repulsive Forces of the Sun in the Tails of Comets”), in Astronomicheskii zhurnal,8, no. 3–4 (1931), 199–205; “Stereoskopichesky metod fotografirovania komet” (“The Stereoscopic Method of Photographing Comets”), ibid., 9, nos. 1–2 (1932), 71–81; “O dvizhenii oblachnykh obrazovany v khvoste komety 1908 III (Morehouse)” (“On the Motion of the Cloud Formation in the Tail of Comet 1908 III…”), ibid., nos. 3–4 (1932), 163–165; Komety(“Comets;” Moscow, 1935); “Spectroskopia komet” (“Spectroscopy of Comets”), in Uspekhi astronomicheskikh nauk,4 (1935), 46–60; “Stroenie golovy komety” (“Structure of the Head of a Comet”), in Astronomicheskii zhurnal, 12, no. 1 (1935), 1–20; and “Origin of Sporadic Meteors,” in Observatory,59, no. 743 (1936), 132–135.

Subsequent writings are “Vidimye radianty kosmiches-kikh meteornykh potokov” (“Visible Radiants of Meteor Showers in Space”), in Astronomicheskii zhurnal, 13 (1936), 388–396; “Mnogoyarusnye obolochki komet s khvostami 1 tipa” (“Many-Layered Envelopes of Comets With Tails of Type I”), ibid.,14, no. 2 (1937), 130–134; “Evolyutsia i proiskhozhdenie komet” (“Evolution and Origin of Comets”), ibid., 16, no. 1 (1939), 3–27; “Istoria Gosudarstvennogo astrofizicheskogo instituta, 1922–1931” (“History of the State Astrophysical Institute…”), in Uchenye zapiski Moskovskogo gosudarstvennogo universiteta,58 (1940), 121–136; “Proiskhozhdenie komet” (“Origin of Comets”), in Uspekhi astronomicheskikh nauk (1941), no. 2, 101–121; ’Isklyuchiteinye komety. Bolshaya sentyabrskaya korneta 1882 II“ (“Exceptional Comets. The Great September Comet 1882 II”), in Astronomicheskii zhurnal,21, no. 5 (1944), 201–202; Priroda komet (“The Nature of Comets”; Moscow, 1944); Golova komety i novaya klassifikatsia kometnykh form (“Head of a Comet and a New Classification of Comet Forms”; Moscow, 1945); “Moshchnost i svetosila astrografa i spektrografa” (“Power and Optical Efficiency of the Astrograph and Spectrograph”), in Astronomicheskii zhurnal22 , no. 1 (1945), 1–10; and “Sinkhrony v khvostakh komet” (“Synchrones in the Tails of Comets”), ibid., no. 4, 202–214.

Later works arc “Rol’ F. A. Brcedikhina v razvitii mirovoy nauki” (“The Role of F. A. Bredikhin in the Development of World Science”), in Uchenye zapiski Moskovskogo gosudarstvennogo universiteta, no. 91 (1947), 157–185; Fedor Aleksandrovich Bredikhin, 1871–1904 (Moscow, 1948); “Komety,” in Astronomia v SSSR za tridtsat let. 1917–1947 (“Astronomy in the USSR for Thirty Years…”) Moscow, 1948), 83–88;“ Asleroidy i meteority” (“Asteroids and Meteorites”), in Meteoritika, no. 5 (1949), 3–13; “Meteornye potoki i komety” (“Meteor Showers and Comets”), in Astronomicheskii zhnrnal,17, no. 1 (1940), 4–7; “Reflektory Maksutova i Shmidta” (“The Reflectors of Maksutov and Schmidt”), ibid.,30, no. 5 (1953), 546–551; “Rol basis pri opredelenii meteornykh orbit” (“The Role of the Basis for the Determination of Meteor Orbits”), in Byulleten Komissii po kometam i meteoram Astrosoveta, Akademiya nauk SSSR, no. 1 (1954), 24–28; and “Komety,” in Astronomia v SSSR za 40 let (“Astronomy in the USSR for Forty Years”; Moscow, 1960), written with S. M. Poloskov.

II. Secondary Literature. See “Chestvovanie chlenakorrespondenta AN SSSR S. V. Orlova” (“Celebration in Honor of Associate Member… Academy of Sciences…”), in Vestnik Akademii nauk SSSR (1951), no. 6, 81–83; “Orlov, Sergey Vladimirovich,” in Bolshaya Sovetskaya entsiklopedia (“Great Soviet Encyclopaedia”), 2nd ed., XXXI (1955), 203; S. M. Poloskov, “Vydayushchiysya issledovatel’ komet S. V. Orlov (k 70-letiyu so dnya rozhdenia)” (“Outstanding Investigator of Comets S. V. Orlov [on His Seventieth Birthday]”), in Priroda (1951), no. 11, 73–75; “S. V. Orlov (k 75-letiyu so dnya rozhdenia” (“…on His Seventy-Fifth Birthday”), in Byulleten Stalinabadskoi astronomicheskoi observatorii, no. 14(1955), 3–4; “S. V. Orlov (Nekrolog),” in Astronomicheskii tsirkulyar Akademii nauk SSSR, no. 190 (1958), 1–3; “Semidesyatiletie S. V. Orlova” (“Seventieth Birthday of S. V. Orlov”), in Byulleten Vsesoyuznogo astronomogeodezicheskogo obshehestva, no. 10 (1951), 3–4; “Sergey Vladimirovich Orlov (k 40-letiyu nauchnoy i pedagogicheskoy deyatelnosti)” (“…on the Fortieth Anniversary of His Scientific and Teaching Career”), in Tsirkulyar Stalinabadskoi astronomicheskoi observatorii,nos. 64–65 (1948), 1; and “Sergey Vladimirovich Orlov (nekrolog),” in Astronomicheskii zhurnal.35, no. 3 (1958), 321–322.

P. G. Kulikovsky