Adriaan Van Maanen's Influence on the Island Universe Theory: Part 1

Kant I. , Allgemeine Naturgeschichte und Theorie des Himmels (Leipzig, 1755).

Earl of Rosse (William Parsons), “Observations on the Nebulae”, Philosophical transactions of the Royal Society, cxl (1850), 499.

The proceedings of the debate are published in: Shapley Harlow and Curtis Heber D. , “The Scale of the Universe”, Bulletin of the National Research Council, ii (1921), 171–217. These ‘proceedings’ are fundamentally different from what actually took place.

More information can be found in: Fernie J. D. , “The Historical Quest for the Nature of the Spiral Nebulae”, Publications of the Astronomical Society of the Pacific, lxxxii (1970), 1189–230; Hetherington N. S. , “The Shapley-Curtis Debate”, Leaflets of the Astronomical Society of the Pacific, April 1970; Struve O. and Zebergs V. , Astronomy of the twentieth century (New York, 1962); Struve O. , “A Historical Debate about the Universe”, Sky and telescope, xix (1960), 398–401. (Certain of these articles, however, are based only on published sources and contain some fundamental errors.) Berendzen R. and Hoskin M. are preparing a detailed account of the debate with transcripts of pertinent documents, both published and archival.

A biographical article on van Maanen by Berendzen R. and Shamieh C. is being published in Dictionary of scientific biography (New York, in progress).

van Maanen A. , The proper motions of 1418 stars in and near the clusters h and X Persei (Utrecht, 1911).

Slipher V. M. detected both radial and rotational motions in several spiral nebulae; e.g., “Spectrographic Observations of Nebulae”, Popular astronomy, xxiii (1915), 21–24. Wolf M. found evidence of rotation in the spiral M81: Astronomische Gesellschaft, xlix (1914), 162. There were also several announcements of motions in non-spiral type nebulae. For more details, see Fernie , op. cit. (ref. 4).

van Maanen A. , “Preliminary Evidence of Internal Motion in the Spiral Nebula Messier 101”, Astrophysical journal, xliv (1916), 210–28.

van Maanen A. , “Preliminary Evidence of Internal Motion in the Spiral Nebula Messier 101”, Proceedings of the National Academy of Sciences, ii (1916), 386–90.

Op. cit. (ref. 8), 219.

Letter, A. van Maanen to G. E. Hale, 29 April 1916 (George Ellery Hale Papers, 1882–1937, Microfilm Edition, California Institute of Technology, Pasadena, 1968; there are also copies at the American Institute of Physics, New York and at Boston University).

van Maanen A. , “The Relative Proper Motions of 162 Stars in the Neighborhood of the Great Nebula in Orion”, Astronomical journal, xxvii (1912), 139–46.

van Maanen A. , “The Photographic Determination of Stellar Parallaxes with the 60–inch Reflector”, Mount Wilson contributions, no. 111 (1915), 1–33.

Letter, van Maanen A. to Hale G. E. , 31 October 1916, op. cit. (ref. 11).

Op. cit. (ref. 8), 219–20.

Ibid., 224.

Van Maanen also used an estimate of parallax based on the assumption that the relations among proper motion, distance, and magnitude applied to spirals as well as to stars. Apparently, this is the relation discovered by Kapteyn J. C. , “On the Mean Parallax of Stars of Determined Proper Motion and Magnitude”, Publications of the Astronomical Laboratory at Groningen, no. 8 (1901). Unfortunately, van Maanen did not give a reference for the method, did not justify his assumption that spirals are of twelfth magnitude, and did not supply details of the calculation, which yielded a mean parallax of 0'·005.

Curtis H. D. , “Proper Motions of the Nebulae”, Publications of the Astronomical Society of the Pacific, xxvii (1915), 214–18.

Space velocity refers to the total linear velocity of spirals, which can be resolved into two orthogonal components: The radial velocity and the tangential velocity (V_T). Also note that proper motion, μ, refers to the angular motion of a nebula as a whole across the sky, and should not be confused with motion within the nebula. It can be resolved into components by: μ = (μδ² + μ_α² cos²δ)^1/2. Curtis discussed the total proper motion, while van Maanen was interested in internal motions.

Although the radial and rotational velocities found by Slipher were of the same order, there is no physical connection between them. The similarity was entirely coincidental.

Van Maanen's results for the solar magnetic field were subject to systematic errors, as has been discussed by Stenflo J. , “Hale's Attempts to Determine the Sun's General Magnetic Field”, Solar physics, xiv (1970), 263–73.

The results were summarized in “Internal Motion in Four Spiral Nebulae”, Publications of the Astronomical Society of the Pacific, xxxiii (1921), 200–2. The measures of each spiral were published separately: “Investigations on Proper Motion, Fourth Paper: Internal Motion in the Spiral Nebula Messier 51”, Astrophysical journal, liv (1921), 237–45; “Investigations on Proper Motion, Fifth Paper: Internal Motion in the Spiral Nebula Messier 81”, Astrophysical journal, liv (1921), 347–56; “Internal Motion in the Spiral Nebula Messier 33”, Proceedings of the National Academy of Sciences, vii (1921), 1–5.

Letter, Duncan J. C. to Slipher V. M. , 14 July 1916 (Lowell Observatory Archives).

Letter, van Maanen A. to Shapley H. , 5 June 1921 (Harvard University Archives).

Letter, van Maanen A. to Hale G. E. , 11 July 1917, op. cit. (ref. 11).

It is surprising that van Maanen was unable to find motions in M31, which we now know to be the nearest spiral, while he was able to find motions in others, which are immensely more distant.

Letter, van Maanen A. to Hale G. E. , 17 December 1917, op. cit. (ref. 11).

“Internal Motions in the Spiral Nebula Messier 33” (ref. 22), 1.

Ibid.

van Maanen A. , “Investigations on Proper Motion, Seventh Paper: Internal Motion in the Spiral Nebula NGC 2403”, Astrophysical journal, lvi (1922), 200–7.

van Maanen A. , “Investigations on Proper Motion, Eighth Paper: Internal Motion in the Spiral Nebula M94 = NGC 4736”, Astrophysical journal, lvi (1922), 208–16.

van Maanen A. , “Investigations on Proper Motion, Ninth Paper: Internal Motion in the Spiral Nebula Messier 63, NGC 5055”, Astrophysical journal, lvii (1923), 49–56.

van Maanen A. , “Investigations on Proper Motion, Tenth Paper: Internal Motion in the Spiral Nebula Messier 33, NGC 598”, Astrophysical journal, lvii (1923), 264–78.

He also discussed errors in several later papers. See §4.

See §3.2.

Shapley H. , “On the Existence of External Galaxies”, Publications of the Astronomical Society of the Pacific, xxxi (1919), 261–8.

Shapley's debate manuscript can be found in the Harvard University Archives, and sections of it will be reproduced in the forthcoming Berendzen and Hoskin article (see ref. 4).

Shapley H. , Through rugged ways to the stars (New York, 1969), 79.

Letter, Shapley H. to Russell H. N. , 31 March 1920 (Harvard University Archives).

Letter, Shapley H. to Russell H. N. , 3 September 1917 (Harvard University Archives).

Letter, Russell H. N. to Shapley H. , 8 November 1917 (Princeton University Archives).

Letter, Shapley H. to Curtis H. D. , 24 October 1920 (Harvard University Archives). Note that Shapley mentioned results for M33 which van Maanen had not yet published.

Letter, Shapley H. to van Maanen A. , 8 June 1921 (Harvard University Archives).

Letter, van Maanen A. to Russell H. N. , 7 September 1920 (Princeton University Archives).

Letter, Russell H. N. to van Maanen A. , 5 October 1920 (Princeton University Archives).