# Orlov, Aleksandr Yakovlevich

# ORLOV, ALEKSANDR YAKOVLEVICH

(*b*. Smolensk, Russia, 6 April 1880; *d.* Kiev, Ukrainian S.S.R., 28 January 1954) *astronomy, gravimetry, seismology.*

The thirteenth child of a priest, Orlov graduated from the Voronezh Gymnasium in 1898. He revealed a strong interest in astronomy while attending the mathematical section of St. Petersburg University; a student work published in 1901 on the total solar eclipse of 1907 was awarded a prize by the Society of Natural Scientists. He graduated with distinction in 1902 and the following year broadened his scientific background by studying at the Sorbonne, at Lund with C. L. W. Charlier, and at Göttingen with Johann Wiechert.

In 1905-1906 Orlov was an assistant at the Yurev [now Tartu, Estonian S.S.R.] observatory and inspected seismic stations in Transcaucasia for the Permanent Central Seismic Commission. At Pulkovo observatory (1906-1908) he made observations on the zenith telescope, analyzed observations, and improved existing methods. In 1908 he returned to Yurev to undertake seismic research, and in 1909 he became director of the seismic station of the Yurev observatory. He was an active member of the Permanent Central Seismic Commission in his capacity as representative of Yurev University, where he also lectured on seismology, the theory of seismic instruments, celestial mechanics, and geodesy. His remarkable series of observations on tidal lunar-solar deformations of the earth, made with the horizontal pendulum, provided the subject of his thesis, defended in 1910 at St. Petersburg, for the degree of master of astronomy and geodesy. In July 1911 Orlov was one of three Russian delegates to the congress of the International Seismological Association at Manchester, at which he was elected a member of the international commission for the study of tidal deformations of the earth. In 1911, on the recommendation of the congress, he organized a new seismic station in Tomsk. He also visited Yerkes Observatory in connection with his research on the motion of matter in comet tails. In the summer of 1912 Orlov took part in a major gravimetric expedition to western Siberia. In December of that year he was named extraordinary professor at Novorossysk University in Odessa and director of the Odessa observatory. After defending his doctoral dissertation in 1915, he became professor at Odessa University, where he taught spherical and theoretical astronomy, celestial mechanics, and advanced geodesy.

After the 1917 Revolution, Orlov took part in renewing the destroyed triangulation network of southern Russia from the Dnieper to the Dniester rivers. In 1921 he organized computation and publication of the marine astronomical yearbook, issued until 1924. Remaining as director of the Odessa observatory, Orlov was elected rector of Kiev University in 1919 and from 1920 to 1923 was academician of the Academy of Sciences of the Ukrainian S.S.R. In 1924 a gravimetric observatory was organized, at Orlov’s suggestion, in Poltava, to produce gravimetric maps of the Ukrainian S.S.R. and to study tidal deformations of the earth and polar perturbation. In 1926 this observatory began to conduct regular work at Poltava and gravimetric expeditions.

In 1927 Orlov was elected corresponding member of the Soviet Academy of Sciences; from 1934 to 1938 he was professor of astronomy at the P. K. Sternberg Astronomical Institute in Moscow. From 1938 to 1951 he again headed the Poltava observatory, and in 1939 he became a member of the Academy of Sciences of the Ukrainian S.S.R. While he was director of the Main Astronomical Observatory of the Academy (1944–1950) construction was begun on a new observatory in Goloseevo, near Kiev. At Orlov’s initiative the first All-Union Conference on Latitude was held in October 1939; on its recommendation a commission on latitude of the Astronomical Council of the Soviet Academy of Sciences was created. Orlov was its president until 1952.

Orlov’s scientific work touched on several areas: (1) the motion of the poles and variations in latitude; (2) tidal deformations of the earth; (3) seismology; and (4) geodesy and geophysics. He also studied comets, the rotation of the sun, precalculations of the circumstances of solar eclipses, problems of theoretical astronomy, analysis of curves of brightness of variable stars, and curves of radial velocities of spectroscopic binary stars.

Work in the first area inaugurated a yearlong series (1906–1907) of extremely precise observations on the zenith telescope at Pulkovo. Orlov developed a graphic method of selecting pairs of stars for determining latitudes (so-called latitude pairs) from observations by the method of equal zenith angles. A group of works beginning in 1916 was completed with the publication of articles that were of great importance in interpreting the results of observations of the International Latitude Service. Orlov introduced a new definition of the concept of “mean latitude” and, using harmonic analysis of the variations of altitude of the pole, confirmed Chandler’s indication that there were variations of latitude besides the fourteen-month period in the motion of the pole.

At the Poltava gravimetric observatory, extensive observations were begun on the two bright stars α a Persei and α Ursae Majoris, which could be observed there at their highest culmination near the zenith both day and night. Orlov proposed the establishment of stations at the same latitude, at Blagoveshchensk (on the Amur River) and Winnipeg, Canada.

Orlov discovered slow nonpolar variations of latitude and devised a method for excluding them and for correcting the polar coordinates for the period during which the International Latitude Service existed (1892–1952). His numerous investigations led him to develop a new method of determining the polar coordinates from latitude observations at an isolated station.

Orlov’s last works deal with an explanation of semimonthly changes in latitude and with the determination of the coefficients of the principal member of nutation based on declination. A posthumously published work on secular polar motion contains a vast amount of observational and theoretical material (259,000 observations of latitude) on the basis of which Orlov discovered the annual secular motion of the pole to be 0.004˝ per year, proceeding along a meridian of 69° W.

Orlov’s son Boris (1906–1963) was an astrometrist at Pulkovo. His son Aleksandr (*b*. 1915) became a specialist in celestial mechanics at the P. K. Sternberg Astronomical Institute.

## BIBLIOGRAPHY

I. Original Works. Orlov’s selected works were published as *Izbrannye trudy,***3** vols. (Kiev, 1961). His writings include “O polnom zatmenii Solntsa 1907 goda” (“On the Total Solar Eclipse of 1907”), in *Izvestiya Russkago astronotmicheskago obshchestva,* no. **9** (1901), 48-52, with map; and *ibid.,* no. 10 (1903), 131–145; “Nablyudenia potoka Perseid v 1901 g., sdelannye v Pulkove” (“Observations at Pulkovo on the Stream of Perseids in 1901”), in *Izvestiya Imperatorskoi akademü nauk,***36** (1902), 45–52; “Sur la théorie des appareils seismiques,” in *Bulletin astronomique,***23** (1906), 286–291; “Über die Untersuchungcn der Schwankungen der Erdrinde,” in *Protokoly Obshchestva estestvoispytatelei pri Imperatorskom yurevskom universitete,***15** no. 3 (1906), 147-162; “Über die von Fürst Golitzin angestellte Versuch mit einem nahezu aperiodischen Seismographen,” *ibid.,* 167–173; “Beobachtungen am grossen Zenitellescop von 7 Februar 1907 bis zum 28 Februar 1908,” in*Publications de l’Observatoire central (Nicolas) à Poulkova,* 2nd ser., **18** (1908)1–66;“Ob opredeleny postoyannykh *k* i n uravnenia *d ^{2}θ/dt^{2} + 2k(dθ/dt) + n^{2}θ*=0” (“On the Determination of the Constants

*k*and

*n*of the Equation…”), in

*Protokoly Obshchestva estestvoispytatelei pri Imperatorskom yurevskom universitete,*

**10**, pt. 4 (1908), 243–258; “Graphische Methode zur Auswahl der Sternpaare für die Breitenbestimmung nach der Methode gleicher Zenitdistanzen,” in

*Trudy Astronomicheskoi observatorii, Yurevskogo universitet,*

**21**, pt. 2 (1909), 3–12; “Beobachtungen über die Deformation des Erdkörpers unter dem Attractionseinfluss des Mondes an Zöllner’schen Horizontalpendeln,” in

*Astronomische Nachrichten,*

**186**(1910), 81–88; and “Novy sposob opredelenia velichiny ottalkivatelnoy sily Solntsa” (“A New Method for Determining the Value of the Repulsive Force of the Sun”), in

*Izvestiya Imperatorskoi akademü nauk*no. 7 (1910), 517–522.

Subsequent works include “Pervy ryad nablyudeny s gorizontalnymi mayatnikami v Yurieve nad deformatsiami Zemli pod vlianiem lunnogo prityazhenia” (“First Series of Observations with the Horizontal Pendulums at Yurev on the Deformation of the Earth Under the Influence of Lunar Gravity”), in *Trudy Astronomicheskoi observatorii, Yurevskogo universiteta,***23** , pt. 1 (1911), his master’s diss.; “Sur la théorie des queues des comètes,” in *Astronomische Nachrichten,***196** (1914), 231; “Über der ursprüngliche Bredichinsche Teorie des Kometcnschweife,” *ibid.,***198** (1914), 161; “Opredelenie sily tyazhesti v Zapadnoy Sibiri” (“Determination of the Force of Gravity in Western Siberia”), in *Trudy Astronomicheskoi observatorii* (Odessa), no. 1 (1914), 1–22; “Rezultaty yurievskikh, tomskikh i potsdamskikh nablyudeny nad lunnosolnechnymi deformatsiami Zcmli” (“Results of Yurev, Tomsk, and Potsdam Observations on the Lunar-Solar Deformation of the Earth”), *ibid.,* no. 2 (1915), 1–281, his doctoral diss.; “Rezultaty 18-letnego ryada nablyudeny solnechnykh pyaten, proizvedennogo v Odesse s Konstantinovskim geliografom” (“Results of an Eighteen-Year Series of Observations of Sunspots Made at Odessa With a Constantinov Heliograph”) in *Izvestiya Imperatorskoi akademü nauk,*no. 2 (1915), 135–144; *Teoreticheskaya astronomia s prilozheniem tablits*(“Theoretical Astronomy with Appended Tables”;Odessa, 1920); Odessa Astronomical Observatory,“Harmonic Analysis of the Latitude Observations, I. Kazan, Carlo-forte, Greenwich” (Odessa, 1925), 7–30; “Harmonic Tables for Spectroscopic Binaries,”*ibid*., (1930), 1–8; “Über die Dreiachsigkeit des Trägheitsellipsoids der Erde aus Breitenbeobachtungen,”in *verhandlungen der siebenten Tagung der Baltischen geodetischen Kommission* (1934), 319–339; and “Opredelenie lunnykh geomagnitnykh variatsy pri pomoshchi schetnykh mashin” (“Determination of the Lunar Geomagnetic variations with the Aid of Computing Machines”), in *Izvestiya akademii nauk SSSR*, Ser. Geograf. i geofiz., no. 2 (1937), 195–206.

His later works include “O deformatsiakh Zemli po nablyudenium v Tomske i Poltave s gorizontalnymi mayatnikami” (“On the Deformations of the Earth According to Observations in Tomsk and Plotava With Horizontal Pendulums”),ibid., no. 1 (1939), 3-29; Kursteoreticheskoy astronomii (“Course of Theoretical Astronomy” Moscow, 1940), written with his son, Boris; “Dvizhenie zemnogo polyusa po nablyudeniam shiroty v Pulkovo… (“The Motion of the Earth’s Pole According to Latitude Observations at Pulkovo…). in *Byulleten Gosudarstvennogo astronomicheskogo instituta imeni Shternberga,* no. 7 (1941), 5–26; “Dvizhenie mgnovennogo polyusa Zemli otnositelno srednego polyusa za 46 let” (“Motion of the Instantaneous Pole of the Earth Relative to the mean Pole for Forty-Six Years”), *ibid*., no. 8 (1941), 5–34; “On variations of Greenwich Mean Latitude,” in *Doklady Akademii nauk SSSR*, **42** no. 9(1944), 377–381; “On the ‘Ellipcity’ of the Earth’s Equator,” *ibid*., **43** no. 8(1944), 327–328; “ The Mean Annual Motion of the Earth’s Principal Axes of Inertia,” *ibid*., **51** no. 7 (1946), 509; “O vekovom dvizheny polyusov” (“On the Secular Motion of the Poles”), in *O Zadachakh i programme nablyudeny Mezhdunarodnoy Sluzhby Shiroty* (“On the Problems and Program of Observations of the International Latitude Service”; Moscow, 1954), 13–18; “Analiz pulkovskish nablyudeny na zenit-teleskope s 1915 po 1928” (“An Analysis of Observations at Pulkovo on the Zenith Telescope from 1915 to 1928”), in Orlov’s *Izbrannye trudy,* I (Kiev, 1961),234–261; and “Sluzhba shiroty” (“Latitude Service”, *ibid*., 270–334.

II. Secondary Literature. On Orlov and his work, see Z. N. Aksentieva, “Ocherk zhizni i tvorchestva Orlova” (“Sketch of the life and Work of Orlov”), in *Izbrannye trudy*, I, 3–37; and the obituary by Z.N.Aksentieva and V.P. Fedorov, in *Trudy Glavnoi astronomicheskoi observatorii v Pulkove*, no 146(1954).

P. G. Kulikovsky

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**Orlov, Aleksandr Yakovlevich**