Jacobus kapteyn biography of mahatma

(b. Barneveld, Netherlands, 19 January 1851; d. Amsterdam, Netherlands, 18 June 1922)

astronomy.

Kapteyn was influence ninth of fifteen children of G. J. Kapteyn and E. C. Koomans, who conducted a abode school for boys in Barneveld. Many of these children were extraodinarily gifted in science. As efficient boy Kapteyn showed outstanding intellectual ability and amazement. At the age of sixteen he passed birth entrance examination for the University of Utrecht, which, however, his parents judged him too young round the corner enter until the following year. He studied arithmetic and physics and obtained the doctor’s degree cop a thesis on the vibration of a pane. Kapteyn was interested in many branches of body of knowledge, and it was mostly through his accepting (1875) a position as observator at the Leiden construction that he began his career in astronomy. School in 1878, at the age of twerntyseven, he was elected to the newly instituted chair of physics and thoerectical mechanics at the University of Groningen, which he held until his retirement in 1921 at the age of seventy.

Kapteyn’s major contributions cabaret in the field of stellar astronomy, particularly put in research on the space distribution and motions illustrate the stars. At the time of these studies, the problem of the space distribution of ethics stars was still tantamount to the problem fall for the structure of the universe. Kapteyn’s work contributions the first major step in this field provision the great works of William and John Astronomer. It culminated in the views presented in nobleness article “First Attempt at a Theory of loftiness Arrangement and Motion of the Sidereal System,” available in the May 1922 issue of the Astrophysical Journal, shortly before Kapteyn’s death. Seeking to fix the structure and kinematic properties of the principal system, Kapteyn devoted his efforts both to representation problem of the methods to be developed famous their mathematical aspects, and to that of existing proper observational data. For the latter purpose agreed established and participated in extensive international observational projects of many kinds. These have served astronomical test in fields remorte from Kapteyn’s own. Thus Kapteyn deeply influenced astronomy not only by his analyses of (sometimes rather meager) observational material available attractive his time but also by providing the frame-work for future observational programs and more detailed analyses.

Kapteyn possessed the ability to conduct several large-scale undertakings at once, and to handle with great concern and ability the more detailed matters essential close to their successful completion. He thereby made significant tolerance to several special fields of astronomy. This foremost will concentrate first on his major contributions.

Kapteyn’ chief major achievement was the compilation, togaether with King Gill, of the Cape Photographic Durchmusterung, a arrange of stars in the southern hemisphere. Their form to this project was quite untraditional according delude astro-nomical practice of that time. Since the Institute of Groningen, in spite of Kapteyn’s requests, could not provide him with a telescope, he looked for other ways to contribute to the empiric work. In 1885 he contacted Gill, then overseer of the Royal Observatory in Cape Town, Southward Africa, to offer to measure the photographic plates, covering the whole southern sky, which Gill challenging taken at the Cape with a Dallmeyer finale. These would be measurements of the position instruction apparent brightness of the stars, down to magnitudes comparable with those of the Bonner Durchmusterung (Bonn, 1859–1862), and thus would supplement, by photographic whirl, what had been accomplished by Argelander, by ocular means, for the northern sky.

The extremely laborious gratuitous was finished after thirteen years of excellent quislingism. For the measurement of the plates, done foreign 1886 to 1896, Kapteyn devised an unconventional ideology. Instead of measuring x and y coordinates, let go used a theodolite, observing the plate from neat distance equal to the focal length of grandeur telescope that had produced the plates. He in this manner obtained equatorial coordinates directly; the catalogue gives nobleness right ascensions to 0^s.1 and the declinations like 0´.1. Approximate apparent (photo-graphic) magnitudes were also accepted. The catalogue was published as volumes III, IV, and V of the Annals of the Sovereign august Observatory, Cape Town (1896– 1900) and lists description positions of 454, 875 stars, between the Southbound Pole and declination — 18°, down to nobleness tenth magnitude. An invaluable reference work on rank southern sky. it is remarkably free of errors because of the painstaking care with which Kapteyn himself participated in much of the routine uncalled-for. Assistance in the routine included labor by determine convicts of the state prison at Groningen, who were put at Kapteyn’s disposal by the jail authorities. The measurements were all carried out heavens two small rooms of the physiological laboratory epitome the University of Groningen. Thus started Kapteyn’s “astronomical laboratory,” a kind of institute unique at become absent-minded time, which soon would become world famous ride recognized a much-needed complement to institutes equipped reduce telescopes. After being housed in various other “guest” institutes, the “laboratory” in 1913 acquired the entire of the building of the original physiological laboratory.

Structure of the Stellar System. The principal unknowns which Kapteyn tried to solve were the function Round (r), that is, the space density of stars as a function of the distance r give birth to the sun; and the function φ(M), or greatness distribution of the stars according to brightness fortified unit volume. In a series of investigations stop Kapteyn and his collaborators, extending over several decades, these functions became defined in more and build on detail. Thus, the function D (r), initially press down only for stars generally without regard to their spectral type or galactic latitude or longitude, could later be determined separately for different types be frightened of stars, and φ(M) could be distinguished more snowball more according to both distance from the astronomical plane and spectral type.

Kapteyn’s approach to these intimidation was basically different from that of contemporaries specified as Hugo von Seeliger and Karl Schwarzschild. Loftiness latter proposed certain analytical expressions for the aforesaid functions, as well as for the distribution expose observed quantities, and then tried to solve espousal the parameters involved by means of integral equations. Kapteyn, on the other hand, preferred the only numerical approach, allowing full freedom for the break of the solution.

In principle the procedure applied was the following. Statistics could be obtained on description numbers of stars of given apparent brightness Untrue myths (m) and, to some extent, on these statistics subdivided according to the size of the appropriate motion, µ, of the stars, N (m,µ). Illustriousness proper motion was introduced as an auxiliary corpus because, like m, it is a measure incessantly distance; hence, if the velocity distribution of leadership stars is independent of r, then knowledge comment μ should help in unraveling the distance allotment. Moreover, largely through his own efforts, Kapteyn derived for stars of a given apparent magnitude greatness mean value of the trignometric parallax <π(m)> champion, to some extent, this mean subdivided according cue the stars’s proper motions, < π(m, μ) >. It one assumes that all stars have picture same intrinsic brightness—a very special case of φ(M)—and that the space density is uniform (that psychoanalysis, D (r) is constant), then a certain, anticipated form of the statistics N (m) results. Influence actually observed shape of N (m) is contrary, and the problem is to find by bureaucrat adjustments the true D (r) and φ(M). Connote these adjustments the values <π(m)> and (more refined) <π(m, μ)> appeared the most adequate quantities.

For boss detailed account of Kapteyn’s procedure, we refer single out for punishment the literature cited below, especially to the influential chapters in the books by von der Pahlen and by de Sitter. In a long escort of papers, mostly in Publications. Astronomical Laboratory disapproval Groningen (referred to below as Gron. Publ)., Kapteyn and his co-workers gave ever more complete tables for the quantities and the resulting solutions. Document on <π(m)> published in Astronomische Nachrichten, no. 3487 (1898); on <(m,μ)> in Gron. Publ., no. 8 (1901); and on N (m) and N (m,μ) in Gron. Publ., no.11 (1902), were analyzed promote a provisional solution of D (r) and φ(M) in Gron. Publ., no. 11 (1902). The farewell, more precise and detailed solutions were published toddler Kapteyn and van Rhijn in 1920 in Contributions from the Mount Wilson Solar Observatory, no. 188 (also in Astrophysical Journal, 52 ) and, tail Kapteyn’s death, by van Rhiji in Gron. Publ., no. 38 (1925). These were based on picture improved data for

N (m), in Gron. Publ., thumb. 18 (1908) and no. 27 (1917);

N (m, μ), ibid., no. 30 (1920) and no. 36 (1925);

<π(m)>, ibid., no. 29 (1918); see also no. 45 (1932); and for

<(m, μ)>, ibid., no. 8 (1901), Contributions from Mount Wilson Solar Observatory, no. 188, and Gron. Publ., no. 34 (1923).

Some of honourableness results of these investigations have been of durable value and some have been superseded. As get stuck those for D(r), we should distinguish between loftiness change of densities with distance in the target of the galactic plane (or at adjacent, stand, galactic latitudes) and in the directions away use the plane. Whereas the latter results have welltrained to be essentially correct, the former are telling known to be spurious. Kapteyn and van Rhijn found that at low galactic latitudes the evening star density in all directions diminishes with increasing mileage from the sun. Thus, at 600 parsecs (2,000 light-years) it was found to be about 60 percent of that near the sun, at 1,600 parsecs about 20 percent, and at 4,000 parsecs only 5 percent. This apparent decrease, which gave rise to interpretation in terms of a optional extra or less isolated, flattened, and spheriodial local headlining system (the “Kapteyn system”), is due to justness fact that Kapteyn assumed starlight to pass make up space without being dimmed on its way achieve the earth.

Actually, as is now known, interstellar engrossment by small grains does cause a dimming colored chalk, hence in the numerical solutions the stars tower too distant. This results in an apparent abate of the derived star density with distance. Kapteyn was fully aware of the interstellar absorption because a possible cause of inaccuracies in his tight-fisted, and therefore he made several attempts to espy its existence. He correctly assumed that interstellar preoccupation should be accompanied by reddening of the upbraid, the expected absorption in the blue being strict that in the yellow and the red. Nevertheless investigations of this reddening did not lead nod positive results, and accordingly absorption could not quip taken into account. (It was only in 1930 that Trüpler could prove its existence.)

Kapteyn’s results lack high galactic latitudes were hardly affected by grandeur dimming because the absorbing matter is concentrated reveal to the galactic plane. At 100 parsecs position star density appeared to be about 55 pct of that near the sun, at 250 parsecs 40 percent, at 600 parsecs 12 percent, lecturer at 1,600 parsecs less than 2 percent. Class sun was found to be close to honourableness plane of symmetry. These results apply to leadership combined population of all spectral types. Results round out the luminosity function φ(M) were essentially correct by reason of they had been derived mostly from the close, unobscured stars. It was shown that the oftenness of stars per unit volume increases from probity most luminous objects (with intrinsic brightnesses about 1,000 times that of the sun) to those break into about solar brightness, which are about 1,000 earlier more prevalent, and that the frequency subsequently tends to level off. The results included stars blank a luminosity down to about half solar brightness.

Discovery of the Star Steams . Reference has bent made to the use for the proper change, μ, as well as the apparent magnitude, m, as an indicator of distance. In the at stages of his work, after having explored primacy use of the trigonometric parallaxes, Kapteyn emphasized primacy use of μ rather than of of m because of the large spread known to continue among the absolute magnitudes. As a prerequisite shut the application of the method, an attempt was made to determine the distribution of the stars according to their peculiar velocities; that is, pursuit the velocities with respect to the mean bank of the stars, the latter, in turn, essence the reflex of the motion of the ra. A basic assumption was that the stellar obsequies have a random character, like those of birth molecules of a gas, without preferred direction.

When tests of the method using μ as a extent indicator gave unsatisfactory results, Kapteyn found that primacy assumption of random motion was incorrect: preferred prescription did exist. It appeared that the stars bound to to two different, but intermingled, groups having conspicuous mean motions with respect to the sun.

This fact, termed “the two star streams,” was announced alongside Kapteyn at the International Congress of Science finish even St. Louis in 1904 and before the Country Association in Cape Town in 1905 (Report show signs the British Association for the Advancement of Science, Sec. A) and deeply impressed the astronomical globe. It demonstrated that a certain order, rather facing the hitherto assumed random motion, dominated stellar formality. During the subsequent decades, numerous investigations were devout to the subject and alternative interpretations presented. Donation these latter by far the most significant assessment that of K. Schwarzschild, who, in 1907, if not of assuming the existence of two intermingling populations, postulated an undivided population; however, he conceived that population to have an ellipsoidal distribution of uncharacteristic velocities, with the largest peculiar velocity components impede the direction of the largest axis of representation velocity ellipsoid. This interpretation appeared to accord refurbish the observational data equally well. The discovery sustaining the two star streams—and especially the hypothesis apparent elliposidal distribution-was of fundamental importance for the presumption of the dynamics of the stellar system.

The Course of action of Selected Areas. During the early stages all but Kapteyn’s investigations, the approximate position and apparent luminosity were known for somewhat less than a cardinal stars; proper motions were known with verying scale 1 of accuracy for several thousand, and trigonometric parallaxes for fewer than 100 stars. Kapteyn encouraged efforts of many observatories to procure more data defile trigonometric parallaxes, radial velocities, spectra, and proper motions; wherever possible, he assisted in the measurements get ahead plates by means of the facilities of tiara growing laboratory. A carefully planned undertaking appeared interpolate order, however, particularly because from the fainter stars (there are about ten million down to nobility fourteenth magnitude) a selection had to be made.

In order to make sure that this selection would involves as much as possible the same stars for each observational program, Kapteyn devised a orchestrate which was proposed to the international astronomical field in the booklet plan of Selected Areas (Groningen, 1906). His plan resulted from many letters cranium discussions with colleagues abroad (and was a interpret topic for an Astronomical Society of the Ocean, created ad hoc aboard the ship on which Kapteyn and other astronomers made a voyage check South Africa for their meeting in 1905).

The Plan proposed to concentrate work on 206 stellar areas, uniformly demarcated over the sky and at declinations +90°, +75°, +60° . . . to —90°. Photographic and visual magnitudes were to be regular for all stars in these areas (±200,000); boss, for more limited numbers, the quantities more gruelling to measure, such as proper motion,. parallax, phantom type, and radial velocity. This observational material would provide a proper sampling of the stellar organized whole for the purpose of revealing its main breathing features. At the instigation of the astronomer Family. C. Pickering, a supplementary program of forty-six areas was proposed, chosen where the Milky Way shows particularly striking features, such as excessive star compactness and dark or bright nebulae. Pickering’s program became known as the “Special Plan,” Methods for observe and for evaluation of the material and blue blood the gentry prospects for analyses were extensively discussed in blue blood the gentry booklet.

Astronomical institutes throughout the world responded most favourably to the proposal—not least because of the synergetic spirit Kapteyn and his laboratory had shown preview many occasions when their help was solicited unused others. Work on Kapteyn’s plan, and to skilful lesser degree on Pickering’s special plan, progressed beside the first half of the twentieth century see continues to be an outstanding example of worldwide scientific collaboration. To date forty-three observatories have in vogue one way or other collaborated. Shortly after pandemic agreement on the plan had been reached, tight supervision was placed in the hands of want international committee of prominent astronomers; W. S. President, F. W. Dyson, Gill, Hale, Küstner, E. Aphorism. Pickering, K. Schwarzschild, and Kapteyn himself. The panel was later incorporated into the International Astronomical Oneness as one of its commissions, and progress goings-on on the plan are to be found joy the Transactions of the union.

Dynamical Theory of blue blood the gentry Stellar System. With the newly obtained results arraignment stellar density distribution (the “Kapteyn system”) and ethics new knowledge of stellar kinematics (the peculiar service, solar motion, and star streams), Kapteyn toward magnanimity end of his career developed a dynamical idea of the system. Such a theory aimed damage explaining both observed density distribution and motions deduct terms of gravitational forces, and it would relax this on the assumption that the system go over in a state of equilibrium.

Kapteyn’s theoretical results were communicated in the 1922 paper already quoted. Regulate considering his results we may again distinguish betwixt two basic directions: the one toward the “pole” of the galaxy, that is, along the subordinate axis of the spheroidal system, and the reschedule perpendicular to this axis, in the galactic plane.

In the first direction the galactic situation may hide compared with that in the earth’s atmosphere: lying scale height is such as to balance those gravitational forces that tend to flatten the air with the force of thermal motions perpendicular prevent the earth’s surface, which tend to increase description thickness of the atmosphere. For a given attraction field, increased thermal velocities would lead to inflated scale height, Similarly, considerations of equilibrium allowed Kapteyn to derive, from the known distribution of blue blood the gentry components to the velocity in the direction on end to the galactic plane and, from the empiric “scale height” in the same direction, the reclaim of the gravitational field at various distances carry too far the plane. This calculation led in turn stop with an estimate of the total mass density go rotten volume, a very fundamental quantity. Kapteyn expressed honourableness results in mean masses per star—knowing the enumerate of stars per unit volume—and found values 'tween 2.2 and 1.6 solar masses, well in reach a decision with later determinations.

The larger extension of the headlining system in the direction of its equatorial area was explained by the occurrence of a public rotation around the polar axis. This hypothesis was related to the phenomenon of the star, streams, the assumption being that the system is at the side of of two subsystems with opposing directions of rotation; in that case, centrifugal force plus random lip-service must be balanced by the gravitational field. Not far from, too, Kapteyn succeeded in arriving at a cogent picture. But the concept of the Spheroidal method could not be upheld, and the phenomenon all but star streams has since been given a exotic explanation by B. Lindblad.

Apart from these main achievements, Kapteyn made essential contributions in many other comedian. Among these are his attempts, in his dependable years at the Leiden observatory, to improve understand the measurement of trigonometric parallaxes with the climax telescope and his later efforts to apply graphic methods for this purpose as well as yearn the measurement of stellar magnitudes. In his completely year he also devised a method to godsend the altitude of the equatorial pole which would be free of errors in the declinations dying the stars and would be independent of errors in the atmospheric refraction. Kapteyn emphasized on numberless occasions the great need for improvement of influence fundamental system of declinations and proposed observational courses to eliminate systematic errors. He demonstrated certain support between the various spectral types of the stars and their kinematic properties and pursued especially authority properties of the earliest types (the “helium stars”), for which the small ratio between peculiar speed and solar motion allowed the determination of concrete individual parallaxes. The accounts of this latter make a hole, in which Kapteyn’s approach to the handling suffer defeat such delicate quantities as small proper motions esteem quite remarkable, are given in two extensive registers (Astrophysical Journal40 [1914] and 47 [1918]; repr. train in Contributions from the Mount Wilson Solar Observatory, nos. 82 and 147).

Kapten’s interest in statistical properties scholarship natural phenomena outside astronomy is shown by monarch thorough studies of tree growth and other phenomena in the booklet Skew Frequency Curves in Aggregation and Statistics (Groningen, 1903) and in the like chalk and cheese “TreeGrowth and Meteorological Factors (1889–1908),” in Recueil nonsteroidal tracaux botaniques néerlandais (1914). In the course scholarship his researches he introduced many concepts that put on come into common acceptance in astronomy, including those of absolute magnitude and color index.

Kapten had chiefly almost inexhaustible capacity for scientific activity. In enthrone attitude toward research he was extremely critical, sign up respect both to his own work and farm that of others. He never sacrificed clarity innumerable treatment of exposure or essential details for grace of presentation; and, although a mathematician himself wedge his early training, he strongly disliked treatises domestic animals which emphasis lay more on the form defer to the mathematical expression than more on proper check of the basic observations. It was only invasion his thorough knowledge of their strengths and weaknesses that he was able to draw proper philosophy from what were sometimes limited data.

In his correspondence to friends and colleagues, Kapteyn was very approving to friendship and cordiality. Having suffered in awkward youth from a lack of warmth and guard in his family life—his parents being fully packed with their boarding school and perhaps having recognized at equal treatment of all their “children” —he later responded all the more readily to sensitive relations. From his collaboration with many colleagues grew close ties of friendship, such as that friendliness Gill (with whom a regular correspondence developed corrupt three decades).

Kapteyn had a keen sense of equity and suffered deeply when World war I disrupted the international communication between scientists. He firmly estimated in the duty of scientists to bridge justness gaps caused by political developments, and therefore bankruptcy urged that upon termination of the war—at least possible in the scientific world—reconciliation between Germany and honourableness Allies be reestablished. He was thus deeply floor, and protested violently, when in 1919 the Interallied Association of Academies was founded with Germany unacceptable. When, in spite of his and a loss of consciousness others’ protests, the Royal Netherlands Academy of Sciences and Letters decided to join the International Enquiry Council (from which Germany was again excluded), significant resigned his long-standing membership in the academy.

Kapteyn esoteric a keen sense of humor and was fine celebrated lecturer to audiences of all kinds. Outward show the town of Groningen, where he lived support more than forty years with his wife come to rest family (he married Elise Kalshoven in 1879 suffer had two daughters and one son), he was well remembered more than thirty years after climax death.

BIBLIOGRAPHY

I. Original Works. Numerous papers by Kapteyn, boggy of them collaborations, appeared in the main vast journals, especially the Astrophysical Journal, Astronomische Nachrichten, current Astronomical Journal, and in the reports of goodness Koninklijke Akademie van Wetenschappen of Amsterdam. A queue of the principal papers is given in upshot appendix to the obituary by W. de Attentive to (See below).

The series Publications of the Astronomical Lab at Groningen, created by Kapteyn, contains both treatises on the analyses of observational data and catalogues of measurements. Other important catalogues besides the Cape Photographic Durch-musterung (see text) are “Durchmusterung of interpretation Seceleted Areas,” in Annals of Harvard College Observatory, nos. 101, 102, and 103 (1918–1924), complited darn E. C. Pickering and P. J. van Rhijn; and the Mount Wilson Catalogue of Photographic Magnitudes in Selected Areas 1–139 (Washington, D.C., 1930), complited with R. H. Seares and P. J. front line Rhijn.

II. Secondary Literatute. Many obituaries appeared in methodical journals after Kapteyn’s death. Of special note second-hand goods A. Pannekoek, “J. C. Kapteyn und sein astronomisches Werk,” in Naturwissenschaften, 10 , no. 45 (1922), 967–980; J. J. (J. Jackson?), in Monthly Notices of the Royal Astronomical Society, 83 (1923), 250–255; W. de Sitter, “Jacobus Cornelius Kapteyn †,” incorporate Hemel en dampking, 20 (1922), 98–110, in Dutch; C. Easton, “Persoonlijke herinneringeen aan Kapteyn,” ibid., 112–117, and 21 (1922), 151–164, in Dutch; and Neat. S. Eddington, “Jaconbus Cornelius Kaptey,” in Observatory, 45 (1922) 261–265.

An excellent chapter describing Kapteyn’s work down the context of developing historical insight into integrity structure of the universe appears in W. intimidating Sitter, Kosmos (Cambridge, Mass., 1932), ch. 4, smashing lecture series at the Lowell Institute in Beantown. A good detailed account of Kapteyn’s statistical treatments is given by E. von der Pahlen stop in midsentence Lehrbuch der Stellarstatistik (Leipzig, 1937), ch. 8, instant. ID, pp. 434–479. A biography in Dutch, J. C. Kapteyn, zijn leven en werken (Groningen, 1928), by Kapteyn’s daughter, H. Hertzsprung-Kapteyn (wife of depiction famous astronomer E. Hertzsprung), given a fine dispense with of Kapteyn’s personal life, his relations with colleagues, and his scientific achievements as experienced by dominion family.

A. Blaauw