This page consists of a chronologically ordered bibliography of articles related to the astrometric measurements of internal motions of stellar systems. (In essense, Adriaan van Maanen resurrected.) The main area of concern has to do with, but is not limited to, spiral nebulae (currently called galaxies). Abstracts, highlights, and thumbnail sketches of a number of the articles, are being added.

The compiler of this bibliography is fully aware that, at the present, about 97 percent of the articles in print since 1935 (and especially those on the world wide web) dealing with van Maanen's sixteen plus Mt. Wilson papers on internal motions of spiral nebulae (published in the 1916-1930 timeframe), paint him as being mistaken in his findings. In contrast to the majority opinion against van Mannen, it can be seen that he was not a lone voice crying in the wilderness. There may even come a need to resume astrometric studies on the internal motions in spiral nebulae.

Journal Abbreviations

1914

Slipher, V. M., "The detection of nebular rotation," Lowell Observatory Bulletin, 2, 66 (1914)
[This pertains to the Virgo Nebula, now known as the Sombrero Galaxy, M104.]

1915

Curtis, Heber D., "Proper Motions of the Nebulae," - PASP, 27, 214-220 (1915)
    [This is a report on an early nebular proper motions study done using photographs made with the Crossley Reflector at Lick Observatory.] The average time between early and late plates was 13.85 years. [pp.214-215]
    The general results [for average yearly proper motions], by classes are as follows:--
1. Large, Diffuse Nebulosities: 0."036 - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10 objects.
2. Planetary and Annular Nebulae: 0."028 - - - - - - - - - - - - - - - - - - - - - - - - - 17 objects.
3. Very Small Nebulae (many show evidence of spiral character ): 0."040  - - - - 47 objects.
4. Large Spiral Nebulae: 0."033 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 66 objects.
[p. 215]
    The accuracy of the measures varies considerably, ... and would be much higher were the old plates as uniformly sharp and good as the late plates. [p.215]
    A number of the better determined nebulae showing numerous condensations were examined graphically for possible evidence of rotation, but none were found..[p. 217]
    The average radial velocity of 73 planetary type nebulae . . . is thirty-nine kilometers per second. This value, combined with the average proper motion found, would make the average distance of this class of nebulae about one thousand light years, a value which is not improbable, as all these objects are Milky Way Phenomena. [p.217]
    The radial velocities of very few spirals have been determined as yet; the mean of SLIPHER'S results is 400 kilometers per second, a truly enormous value, which may be considerably changed when a larger number have been determined. On this basis and on the assumption that these objects are moving truly at random in space, the average distance of the spirals is of the order of ten thousand light years, a distance that many will regard as too small. [pp. 217-218]
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van Maanen, Adriaan, "List of Stars with Proper Motion Exceeding 0".50 Annually," ApJ, 41, 187 (1915)
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Porter, J.G., "Note on van Maanen's list of stars with motion exceeding half a second annually," AJ, 29, 46 (1915)
    These two articles are included because investigations into nebular motions hinged on the use of selecting slowly moving foreground stars as a reference system. [Added 22 March 2010.]

1916

Lampland, C. O., "Preliminary Measures of the Spiral Nebulae N.G.C. 5194 and N.G.C. 4254 for Proper Motion and Rotation," PA, 24, 667 (1916)
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Pease, Francis G., "The Spiral Nebula Messier 33," PASP, 28, 33-34 (1916)
    A spectroscopically determined radial velocity of -278 km/sec for a bright knot some ten minutes of arc from the nucleus of M33, as compared to the systemic [motion as a whole] radial velocity of -70 km/sec, implies some degree of internal motions for the nebula. "Unfavorable weather has prevented the obtaining of spectra of other knots to determine whether there is a progressive change in type from the nucleus to the edge and also whether or not the difference in velocity means a rotation." [See the (1971) Gordon entry below.]
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van Maanen, A., Ritchey, G.W., Keeler, J.E., Perrine, C.D., Curtis, H.D., "Preliminary Evidence of Internal Motion in the Spiral Nebula Messier 101," ApJ, 44, 210 (1916) - [Plate VII is not scanned. NADS abstracts does not list van Maanen's co-authors.]
    See van Maanen's Plate VII that shows his measurements of Internal Motions in Messier 101. [This scanned in image, found with Google.com, was tucked away in the Astronomy and Astrophysics section of Ron Doel's Science in the Twentieth Century webpages. Professor Doel kindly disagrees with this compiler's contention that van Maanen's internal motions of spiral nebulae were unfairly treated by his colleagues.]

1917

Barnard, E. E., "The Proper Motion of the Great Nebula of Andromeda," AJ, 30, 175-176 (1917)
    "Though the distances are discordant, they show that no considerable relative motion has occurred in the past eighty years."
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Jeans, J. H., "Internal Motion in Spiral Nebulae," Obs, 40, 60 (1917)
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Kostinsky, S., "Probable Motions in the Spiral Nebula Messier 51 (Cannes Venatici) Found With the Stereo-comparator. Preliminary Communication," MNRAS, 77, 233 (1917)
    Stereoscopic comparison of plates of Messier 51, taken in March 1896 and in April 1916, found "almost indisputable displacements of some characteristic knots lying on the spirals."... "Preliminary stereoscopic measures on the above-mentioned plates of 36 single knots showed me that their observed proper motions with regard to the centre of the nebula seem to have a systematic character in the different parts. They led me to the following preliminary conclusions: -
    (a) On the outer spiral the motion proceeds as though in general the single parts were moving away from the centre, so that the spiral has a tendency to draw itself together in the direction opposite to the hands of a clock;
    (b) On the contrary, on the inner spiral in its eastern part the motion towards the centre prevails, and if there is any tendency to draw together it is rather in the opposite direction, i.e. with the hands of a clock;
    (c) In the mean the annual proper motions of the single knots and stars are of the order of 0".04 - 0".05, but vary within wide limits.
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Shapley, Harlow, "Note on the Magnitudes of Novae in Spiral Nebulae," PASP, 29, 213-217, (1917)
    Their authenticity [eleven novae in spiral nebulae] can hardly be doubted,   . . .  On the basis of chance, Curtis has noted the impossibility of considering these novae [to be] physically unrelated to the spirals with which they are associated. [p. 214]
    Taking the averages as referring to similar luminosity, possibly an uncertain procedure . . . , we observe that the difference in apparent brightness calls for a distance at least 50 times as great for these larger spiral nebulae as for the average novae of the galactic system. [p. 215]
    If we are to believe that a spiral nebula, . . . , is a remote stellar system, its most luminous stars must be fainter than magnitude 21, since even in its thinner parts there is no hint of resolution into distinct stars on the best of plates; nor can the nebulous condensations, with magnitudes between 15 and 20, be considered an accumulation of stars brighter than magnitude 21. This point is important, for, if in the hypothetical galactic system the brightest stars are comparable with the bright stars of our own galaxy, the minimum distance of the Andromeda Nebula must be of the order of a million light years.

1919

van Maanen, A., "Investigations on proper motion. Second paper: The motions of 162 stars in the neighborhood of the Orion Nebula," Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington, vol. 168, pp.1-15 (1919)
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Schouten, W.J.A., "Probable Motions in the Spiral Nebula Messier 51 (Cannes Venatici)," Obs, 42, 441-444 (1919)
    "The numerous measures performed by Mrs. Dorothea Roberts on photographs of Messier 51 (Rivista di Astronomia, 1910, pp. 31-41 & 62-85) have been published in a form making it impossible (alas!) to deduce the proper-motion of the nebulous points. Therefore we have not been able to compare our results with hers. Kostinsky (Monthly Notices, 1910, pp. 31-41 & 62-85)* has found annual motions of the order 0".04 - 0".05 for a number of points in Messier 51. This agrees with our results"....
    "The rotational movement (2) found for the nebula Messier 51 is considerably smaller than that determined by Dr. van Maanen (Contr. Mount Wilson Observ. No. 118) for the spiral nebula
Messier 101"
    * [Year and page numbers are typographical repeats from Shouten's first reference in the previous sentence. The actual reference is: MNRAS, 77, 233 (1917).]
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van Maanen, A., Willis, H.C., Oosterhoff, P.T., Investigations on Proper Motion, Library of Congress Call Number QB4.M93 no. 167-168, (1919) [Abstract not available.]
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van Maanen, A., "Evidence of Stream Motion Afforded by the Faint Stars Near the Orion Nebula," PNAS 5, 225 (1919)

1920

Curtis, Heber D., "Modern Theories of the Spiral Nebulae," JRASC, 14, 317-327 (1920)
    The most anomalous and inexplicable feature of the spiral nebulae is found in their peculiar distribution. They show an apparent abhorrence for our galaxy of stars, being found in greatest numbers around the poles of our galaxy. In my counts I found an approximate density of distribution as follows:

Galactic Latitude +45° to +90° - - - - - - - - - - - - - - - - - - - - - 34 per square degree.
Galactic Latitude –45° to –90° - - - - - - - - - - - - - - - - - - - - - 28 per square degree.
Galactic Latitude +30° to +45° and –30° to –45° - - - - - - - - - 24 per square degree.
Galactic Latitude –30° to +30° - - - - - - - - - - - - - - - - - - - - - - 7 per square degree.

Part 2

1921

van Maanen, A., "Internal Motion in Four Spiral Nebulae," PASP, 33, 200 (1921)
    For the rotational and radial components the results are collected in Table I. The rotational components would correspond to the following periods: For Messier 101, 85,000 years; for Messier 33, 160,000 years; for Messier 51, 45,000 years; for Messier 81, 58,000 years.
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van Maanen, A. "Investigations on proper motion. Third paper: The proper motions of stars in and near the double cluster in Perseus", Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington, vol. 205, pp.1-29 (1921)

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van Maanen, A., "Investigations on Proper Motion - Fourth Paper: The Internal Motion in the Spiral Nebula Messier 51," ApJ, 54, 237 (1921)
    A comparison of a plate taken by Mr. Duncan on April 8, 1921, with one taken by Mr. Ritchey on February 7-8, 1910, both at the 25-foot focus of the 60-inch reflector, enabled the proper motion of the nebula and the relative motion of its parts to be determined. Measurements of 80 points of the nebula compared with those of 20 stars give for the nebula an annual proper motion of +0".006 in right ascension and +0".001 in declination. The internal proper motion is not a pure rotation since the mean radial component is outward and is 42 percent of the mean tangential component which is 0".019 ENWS; rather it is a spiral motion out along the arms at the rate of 0".021 per year together with a slight outward radial motion of 0".003.
    Two sixteenth magnitude stars with large proper motions, about 0".15 per year, were found near Messier 51. They are called f and r.
    [Plate II (in hardcopy original) shows internal motions of M51.]
    [With respect to his selected reference stars, van Maanen's measures of bulk internal motions for M51 are approximately three times greater than his measure of its systemic proper motion..]
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van Maanen, A., "Investigations on Proper Motion - Fifth Paper: The Internal Motion in the Spiral Nebula Messier 81," ApJ, 54, 347-356 (1921)
    [Plate IV (in hardcopy original) shows internal motions of M81.]

Lundmark, Knut, "The Spiral Nebula Messier 33," PASP, 33, 324-327 (1921)
    On small scale photographs the spiral appears as a bona fide nebulous object but photographed with large instruments especially the outer parts of the spiral arms seem to be resolved into numerous star-like objects. Many of these secondary nuclei look exactly like stars but a number of them have a soft appearance which has led Ritchey to call them nebulous stars.   . . .
    There is in the spiral structure a great number of dark lanes and it is to be noted that these do not always define the space between the spiral arms but many times go across them.   . . . [p. 324]
    [To see an example of a dark lane cutting across spiral arms, see Robert Gendler's CCD photograph
    M81, Spiral Galaxy in Ursa Major.]
    [To this writer, the cross-cutting dark lane phenomenon is suggestive of a wake-like action caused by the rapid passage of some massive object (or a compact system of objects) skimming across the face of a spiral. The object transient time would have to be much shorter than the rotation period of the spiral, otherwise the trace would be curved by the differential motions in the spiral arms. If this is the case, it absolutely requires that the spirals have the relatively small spatial dimensions and distances from us, consistent with van Maanen's findings. RSF 25 Oct 2003.]
    From an unpublished investigation on the proper motion of 100 spiral nebulae, derived from micrometric and photographic measures, we give the following results for N.G.C. 604 [a giant nebulous star forming region in M33] measured as one mass to illustrate the accuracy of the measures. [The units are in decimal fractions of arcseconds per year.] [p. 326]

1922

van Mannen, A., Investigations on proper motion. Sixth paper: The motions of 65 stars in the neighborhood of 65 Tauri", Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington, vol. 224, pp.1-7 (1922)
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van Maanen, A., "Investigations on Proper Motion - Seventh Paper: Internal Motion in the Spiral Nebula NGC 2403," ApJ, 56, 200 (1922)
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van Maanen, A., "Investigations on Proper Motion - Eighth Paper: Internal Motion in the Spiral Nebula M94=NGC 4736," ApJ, 56, 208 (1922)
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1923

Jeans, James Hopwood., The Nebular Hypothesis and Modern Cosmogony: Being the Halley Lecture delivered on 23d May 1922, Oxford, The Clarendon Press, London, New York [etc] H. Milford (1923). [No article or abstract available.]
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Jeans, J. H., "Internal Motions in Spiral Nebulae," MNRAS, 84, 60 (1923)
    No interpretation, and very little discussion, has so far appeared on Mr. van Maanen's highly interesting measurements of the internal motions of spiral nebulae. ... The theoretical part of the present paper has been held back for over a year, the first part of which was spent in an unsuccessful effort to find some less revolutionary interpretation of the observed motions than that here tentatively put forward, the second part being spent in an effort, again unsuccessful, to connect up the suggested interpretation with the general scheme of the theory of relativity....[p. 60] [More to come.]
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van Maanen, A., "Investigations on Proper Motion - Ninth Paper: Internal Motion in the Spiral Nebula Messier 63, NGC 5055," ApJ, 57, 49 (1923)
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van Maanen, A., "Investigations on Proper Motion - Tenth Paper: Internal Motion in the Spiral Nebula Messier 33, N.G.C. 598," ApJ, 57, 264 (1923)

    Comparison of two photographs taken in 1910 and 1922 by Ritchey and Humason, respectively, gives, with respect to twenty-four comparison stars, the annual proper motion of = +0".003, = -0".004, and the motions of 399 nebular points freed from this motion. The internal motions are shown on Plate XIX. They can be interpreted as a rotation or as a motion outward along the arms of the spiral, preferably the latter. Taken as a rotation, the motions indicate periods from 60,000 to 240,000 years. [p. 264]

    There seems to be a considerable increase of motion with distance from the center. Error analysis of measured displacements within seven spirals indicates that actual internal motions exist and are in agreement with Jeans' cosmogony. Parallaxes of larger spiral nebulae suggest diameters ranging from several light years to several hundred light years. Larger spirals are enormous compared to our solar system, but are small compared to the Milky Way. [p. 264.]
    For internal motions expressed as rotation (+ = N-E-S-W) and radial (+ = outward) components, the component means were found to be rotation = +0.020 ± 0.001 arcsec/year, radial = +0.003 ± 0.001 arcsec/year. [p. 273.]

1925

Jeans J. H., "Note on the Distances and Structure of the Spiral Nebulae," MNRAS, 85, 531 (1925)
    Results recently published by Hubble and Shapley seem to establish the inaccuracy of estimates I made some time ago of the distances and other quantities associated with the spiral nebulae. Hubble estimates the distance of M 31 (the Andromeda nebula) as 950,000 light-years, as against my estimate of 5000 light-years. Even apart from this, however, the time has come when my calculations may reasonably be revised in the light of new nebular knowledge.   . . .
    My original calculations made use of v. Maanen's determinations of the angular velocities of the nebulae. Recently Eddington has drawn attention to the close correlation between the luminosities and masses of actual stars. If the same correlation is assumed to hold for the stellar condensations in a nebula, we can dispense with v. Maanen's measurements altogether and (in theory at least) determine the distance of the nebula from the observed stellar magnitudes of its condensations. The method is as follows. [pp. 531-532]
    [Method is described]
    The method, although simple in theory, may encounter in practice a difficulty which may render it almost valueless. [Describes the potential problem.
    [In a footnote Jeans says, "The controversy does not appear to be one between Professor Shapley and myself, so much as one between the estimates of van Maanen and Hubble as to nebular distances."] [p.532]
    [Using Pease's formula for line-of-sight velocity as a function of angular distance from the center of M31, and Hubble's estimated distance to the same object, Jeans arrives at a rotation period for M31 of 18 million years.] [pp. 533-534]
    It is difficult to imagine that those nebulae which exhibit a lenticular centre and filamentous arms with pronounced condensations can have a similar constitution [to that of our galactic stellar system and perhaps to the nucleus of the Andromeda nebula]. It seems more likely that the Andromeda nebula may be in a far later stage of development than the typical spiral; it may exemplify a state intermediate between the typical spiral and the galactic system. [p. 534]
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van Maanen, A., "Investigations on Proper Motion - Eleventh Paper: The Proper Motion of Messier 13 and its Internal Motion," ApJ, 61, 130 (1925)

Part 3

1926

Lundmark Knut, "Internal Motions of Messier 33," ApJ, 63, 67 (1926)
    [T]he motion of translation--the total proper motion of the nebula--was found to be = -0.0015 arcsec/year;
= -0.0050 arcsec/year, which is in good agreement with the corresponding values of van Maanen, namely +0.0034 arcsec/year and -0.0044 arcsec/year, respectively. Internal motions were found to be: rotation = +0.0016 arcsec/year (NESW), and radial = - 0.0057 arcsec/year (outward). [The negative outward measurement may be interpreted as representing an inflowing motion.]

Hubble, E.P., "No. 310. A spiral nebula as a stellar system. Messier 33," Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington, 310, pp. 1 (1926)
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Hubble, E. P., "The Spiral M33 as a Stellar System," ApJ, 63, 236-274 (1926)
    The present contribution to the subject consists of observational data concerning the particular spiral, Messier 33. The data lead to a conception of the object as an isolated system of stars and nebulae, lying far outside the limits of the galactic system. To this extent the evidence favors the island-universe hypothesis, but, in respect to dimensions and luminosity, the spiral is more closely comparable with the Magellanic Clouds than with the galactic system itself. [p. 237. Also, see pp. 273-274.]
    The ratio of minor to major axis appears to be about 2:3; the tilt is therefore about 42°, and the differential velocity of 200 km/sec can be interpreted as the radial component of a linear velocity of rotation about the nucleus of

    *[Strictly speaking, van Maanen was not looking for rotation, rather he was seeking to characterize internal motions whatever their form. To say that van Maanen was doing measures of rotation is to ignore the thrust of his investigation. Further evidence of a lack of communication between Hubble and van Maanen (or something worse) can be seen on page 270. There, Hubble concludes that it is probable that such rapid stars (as mentioned in the preceding paragraph) belong to the nebula. Actually, van Maanen omitted his star No. 367 from the internal motions analysis because its proper motion was so large that he felt it couldn't be part of the nebula. See the last sentence on page 265 of van Maanen's Tenth Paper (1923). ]

[See: Messier 33 Internal Motions on this website.

1927

Lundmark, Knut, "Studies of Anagalactic Nebulae - First Paper," Nova Acta Regiae Societatis Scientiarum Upsaliensis, Volumen Extra Ordinem Editum, (1927).
---

van Maanen, A., "Investigations on Proper Motion - Twelfth Paper: The Proper Motions and Internal Motions of Messier 2, 13, and 56,"
Contributions from the Mount Wilson Solar Observatory, 66, 89-112, (1927); ApJ, 66, 89 (1927)
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van Maanen, A., "Investigations on proper motion. Thirteenth paper: The proper motion of N.G.C. 2264,
Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington, vol. 405, pp.1-6 (1930)
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van Maanen, A., "Investigations on proper motion. Fourteenth paper: The proper motion of six planetary nebulae,"
Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington, vol. 406, pp.1-6 (1930)
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Lindblad, Bertil, "On the Nature of the Spiral Nebulae," MNRAS, 87, 420-426 (1927)
    In his Leçons sur les Hypothèses Cosmogoniques, p. 262, Poincaré attempts to draw a parallel between the figure of a rotating stellar system and the figure of equilibrium of a rotating incompressible liquid. The stellar system is considered in the picture of a gaseous mass with stars as molecules. ...
[p. 420]
    The possibility of explaining the spiral arms rests in this case on principles quite different from those suggested by Poincaré. Our point of departure is simply a theorem on the motion of a material particle under gravitation in the equatorial plane outside of a homogeneous spheroid. ... [p. 422]
    A comparison between such orbits [described above] and the spiral arms of the nebulæ Messier 33 and 81 was made in the paper cited. ...[p. 423] [This may be Hubble, E., ApJ, 64, 349 (1926) or it may refer to an unpublished statistical investigation by Lundmark. Checking.]
    It may be remarked that the arms evidently wind out form the "mother-system" in the same direction as the rotation of the system, while the opposite is the case according to the suggestion by Poincaré.
[p. 425]
    The present theory connects a multitude of facts concerning our stellar system [the Milky Way galaxy] and the spirals, which have only been touched upon very incompletely in this exposition of the general principles. With full appreciation of the beautiful* theory of Jeans, I have therefore ventured to give the present account of the theory which treats the problem from an older, though considerably modified, point of view. [p. 426]
    * [Beware of unrequired adjectives!] [This seems to be one of the seminal papers in the development of one of cosmology's missing mass problems.]

1928

Brown, E. W., "Gravitational Motion in a Spiral Nebula," Obs, 51, 277-286 (1928) [No abstract or article.]
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Curtis, Heber D., "The Unity of the Universe," JRASC, 22, 399 (1928)

1929

Hubble, E. P., "A Spiral Nebula as a Stellar System, Messier 31," ApJ, 69, 103 (1929)
    Resolution. -- The outer regions of the spiral arms are partially resolved into swarms of faint stars, while the nuclear region shows no indications of resolution under any conditions with the 100-inch reflector. Intermediate regions show isolated patches where resolution is pronounced or suggested.
    Distance of M31 derived from Cepheid criteria. -- Comparisons of period-luminosity diagrams indicate that M31 is about 0.1 mag. or 5 percent more distant than M33, and about 8.5 times more distant than the Small Magellanic Cloud. Using Shapley's value for the cloud, we find the distance of M 31 to be 275,000 parsecs.
    Relative dimensions of M31 and the galactic system. -- A tentative comparison of sizes, masses, luminosities, and densities suggests that the galactic system is much larger than M31 but that the ratio is not greater than that between M31 and other known extra-galactic systems.
    Early visual observers of the spectrum reported bright lines on a continuous background. In 1899, however, Scheiner photographed the now familiar solar-type absorption spectrum and announced emphatically that the nebula must be a system of stars. Radial velocities of the order of -300 km/sec. have since been measured by several observers. ... The linear velocity of rotation as indicated by the measures is of the order of 0 .48x km/sec., where x is the distance from the nucleus in seconds of arc. The measures extend to about 150" from the nucleus, and the rotation is in the sense that the south preceding end of the nebula is approaching us relative to the nucleus. [pp 104-105]
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Hubble, Edwin P., "A Relation Between Distance and Radial Velocity among Extra-Galactic Nebulae," PNAS, 15, 168 (1929) - [PNAS PDF. Subscription needed.]

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Markov, A., "On the Nature of Spiral and Gaseous Nebulae," AN, 234, 329 (1929)
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Markov, A., "Verbesserungen zu dem Artikel (On the Nature of Spiral and Gaseous Nebulae)," AN, 234, 329 (1929) [In German.]

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Perrine, C. D., "The Motions and Status of the Spiral Nebulae and Globular Clusters," AN, 236, 329 (1929)

1930

Lemaître, Georges, "On the Random Motion of Material Particles in the Expanding Universe. Explanation of a Paradox," BAN, 5, 273 (1930)
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Perrine, C. D., "The High Velocities of the Spiral Nebulae," AN, 240, 319 (1930)
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van Maanen, A., "Investigations on proper motion. Fifteenth paper: The proper motion of the spiral nebula N.G.C. 4051,"
Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington, vol. 407, pp.1-6 (1930)
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van Maanen, A., "Investigations on Proper Motion - Sixteenth Paper: The Proper Motion of Messier 51, NGC 5194,"
Contributions from the Mount Wilson Solar Observatory, 408, 1 (1930)

Part 4

1931

Humason, Milton L., "Apparent Velocity-Shifts in the Spectra of Faint Nebulae," ApJ, 74, 35-42 (1931)
    With one exception, possibly the velocity of an isolated object seen in projection on a remote cluster, the new data fully confirm the velocity-distance³ previously formulated and extend the observational range to a distance of about thirty-two million parsecs.
    ³It is not at all certain that the large red-shifts observed in the spectra are to be interpreted as a Doppler effect, but for convenience they are expressed in terms of velocity and referred to as apparent velocities.
[p. 35]
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Lemaître, Georges, "Expansion of the Universe, A Homogeneous Universe of Constant Mass and Increasing Radius accounting for the Radial Velocity of Extra-galactic Nebulæ," MNRAS, 91, 483 (1931)
    According to the theory of relativity, a homogeneous universe may exist such that all positions in space are completely equivalent; there is no center of gravity. ...
    Two solutions have been proposed. That of de Sitter ignores the existence of matter and supposes its density to be equal to zero. It leads to special difficulties of interpretation ... but it is of extreme interest as explaining quite naturally the observed receding velocities of extra-galactic nebulæ, as a simple consequence of the properties of the gravitational field without having to suppose that we are at a point of the universe distinguished by special properties.
    The other solution is that of Einstein. It pays attention to the evident fact that the density of matter is not zero, and it leads to a relation between this density and the radius of the universe. This relation forecasted the existence of masses enormously greater than any known at the time. These have since been discovered, the distances and dimensions of extra-galactic nebulæ having become known. From Einstein's formulæ and recent observational data, the radius of the universe is found to be some hundred times greater than the most distant objects which can be photographed by our telescopes. . . .

1933

Lemaître, Georges Edouward, "Discussion on the Evolution of the Universe," [Get ref.]
    [States the theory of the Big Bang.]

1935

[The following two papers are products of the imposed settlement between Hubble and van Maanen on the issue of astrometric evidence of internal motions in spiral nebulae. See: Hubble's Demolition of van Maanen? on this website's Cosmology's Missing Mass Problems page. Scroll down about 2/3rds of the way from the top of that page.]
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Hubble, E., "Angular Rotations of Spiral Nebulae," ApJ, 81, 334-335 (1935)
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van Maanen, A., "Internal Motions in Spiral Nebulae," ApJ, 81, 336-337 (1935) -

1936

Hubble, Edwin, The Realm of the Nebulae, Yale University Press, New Haven (1936), Page 141.
    Messier 33 -- ...The nucleus resembles in appearance a giant globular cluster, although no evidence of resolution is found. It is semistellar, M = -8, spectral type F5, color excess-appreciable, radial velocity, -320 km/sec.*, as derived from moderately large-scale spectra.
    * [A recent best value for M33's systemic heliocentric radial velocity is -180 km/sec. Hubble's disparity may need explaining. See the Gordon (1971) entry below.]
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Humason, Milton L., "Is the Universe Expanding?," ASPL, 2, 161-164 (1936)
    The interpretation of these recessional velocities beyond the observable facts is still controversial. So far as is known at the present time, the only cause which can produce the observed displacements of the lines in the spectrum of a nebula is motion toward or away from us. On the assumption that the displacements represent motion, the observations tell us that almost without exception the extra-galactic nebulae are moving away from us. The most reasonable explanation of this fact at present is that the universe is expanding. [p. 164]
    . . .   If the displacements are not interpreted as motion, we find in the redshifts a hitherto unrecognized and highly important phenomenon whose implications are unknown. [p.164]

1937

Zwicky., F., "On the Masses of Nebulae and of Clusters of Nebulae," ApJ, 86, 217 (1937)

1938

Lindblad, Bertil, "On the State of Motion in the Stellar System and the Probable Relation of the Galaxy to the Sequence of Types of Spiral Nebulae," POBV Conference, 1 September (1938), Page 15 [No abstract or article.]
___

Babcock, Horace W., "Spectrographic Observations of the Rotation of the Andromeda Nebula," (Abstract) PASP, 50, 174-175 (1938)
    The central core of the nebula, to a radius of some 4', appears to rotate with constant angular velocity, in agreement with the results of Pease. A linear velocity of rotation of 90 km/sec in the plane of the spiral is measured at this distance. From this point the velocity falls off, reaching zero at a distance of 10' from the center. Beyond 10', the velocity increases again, in the same direction, and from 22' to 30' maintains a value of about 150 km/sec. [p. 175]

1940

Lindblad, Bertil, "On the Interpretation of Spiral Structure in the Nebulae," ApJ, 92, 1 (1940)
    Previous work had indicated that the full development of spiral structure is likely to give an approximate logarithmic shape of the arms, in which the particles of the arm describe roughly circular orbits of uniform angular velocity around the center. It is concluded here that such a formation is possible. . . .[p.1]
    The verification of the theoretical results by observational data is discussed in some detail. H. W. Babcock's results concerning the rotation of the Andromeda nebula are in good agreement with the main theoretical result concerning the possibility of a uniform rotation of the spiral structure.

1942

Mayall, N.U. and Aller, L.H., "The Rotation of the Spiral Nebula Messier 33," ApJ, 95, 5 (1942)
    ...the velocity of the system is found to be -167 ±5 km/sec...   the main body of the spiral, some 18' in radius, appears to rotate [based on spectroscopic measurements and assumption of simple circular motion in the plane] almost like a solid body (rotational velocity increases fairly uniformly with distance), while the outer parts, represented by a zone having least and greatest radii of 18' and 30' respectively, appear to rotate like a planetary system (rotational velocity decreases with distance). The transition between these two types of motion occurs in the general vicinity of 16' (1000 parsecs) from the center, at which the rotational velocity attains a maximum of approximately 120 km/sec. ... In most of these [earlier] investigations [with the exception of Babcock's study of the Andromeda nebula] the rotational velocities were measured only in the immediate vicinity of the nucleus.

1946

Joy, Alfred H., "Adriaan van Maanen, 1884-1946," PA, 54, 107-110 (1946)
    [According to Joy, van Maanen died of a heart attack on January 26, 1946. His article is a tribute to van Maanen's scientific career. The following quote from the article deals with van Maanen's long term study of internal motions of spiral nebulae.]
    "From 1914 until 1923, in addition to his parallax program, he [van Maanen] spent a great amount of time and effort in an attempt to measure the internal motions in spiral nebulae by comparing plates taken at different epochs from 5 to 15 years apart. Although the material was not homogeneous, some of the plates being taken at the Cassegrain focus, some at the Newtonian, and some even with other instruments, the results were strangely accordant in showing a rotation period of the order of 100,000 years or, perhaps a motion outward along the arms of the spirals. Slow as this motion is, it is much too rapid to be admitted with our present knowledge[*] of the distances of these extragalactic bodies. The fact seems to be that the time intervals between the plates were too short and the observational material inadequate to cope with the difficulties of the problem. For the present, at least, we shall have to rely on spectroscopic results for our picture of the motions in the spiral nebulae." [p. 109]
  *[This would be knowledge based on redshifts being used as measures of cosmological distance. Arp's discordant redshifts, regardless of their ultimate cause, may eventually lead to a re-evaluation of van Maanen's findings.]
    See: Arp, Halton, Seeing Red: Redshifts, Cosmology and Academic Science; Apeiron, Montreal (1998), and Arp, Halton, Research with Fred.[Fred Hoyle]

1948

Milne, E. A., "Star-streaming and the Stability of Spiral Orbits in Spiral Nebulae   I - Motion round a point-nucleus," MNRAS, 108, 309 (1948)

1969

Gordon, Kurtiss J., "History of our Understanding of a Spiral Galaxy: Messier 33," QJRAS, 10, 293-307 (1969) -
http://nedwww.ipac.caltech.edu/level5/March02/Gordon/Gordon_contents.html

1970

Smith, M.G., Weedman, D.W., "Internal Motions in Galactic and Extragalactic H II Regions," ApJ, 161, 33 (1970)
Emission profiles have been observed for the total Hα emission from nine H II regions in the galaxies M101 and M33. ... The most probable velocities of internal motions are found to range from 19 to 34 km sec^-1. [Added 07 Feb 2007.] [Chandar (2002) found young cluster velocities of 87 ± 11 km sec^-1 in M33.]

1971

Berendzen, Richard,; Hoskin, Michael, "Hubble's Announcement of Cepheids in Spiral Nebulae," ASPL, 10, 425 (1971)
___

Gordon, Kurtiss, J., "A 21-CENTIMETER Study of the Spiral Galaxy Messier 33," ApJ, 169, 235-270 (1971)
    The "best value" for the systemic radial velocity of M33 is S = -180 km/sec (heliocentric). The rotation peaks at Vr = S ± ~85 km/sec at 30' from the galactic center. ...Velocities in the wings deviate by 40-50 km/sec from those predicted by the rotation curve. [Measures of the systemic velocity for M33, since 1942, have been within eight percent of Gordon's "best value" of -180 km/sec. It is of interest to note that in 1916 Pease's measurement was -70 km/sec and in 1936 Hubble's stated value was -320 km/sec. Hubble did not specify who made the measurements.]

See: Systemic Radial Velocity Measurements of Messier 33. [This website]

Part 5

1973

Hart, Richard Cullen, "Adriaan van Maanen's Influence on the Island-Universe Theory," Thesis (Ph.D.)--Boston University Graduate School, (1973). Source: Dissertation Abstracts International, Volume: 34-04, Section B, page: 1356 (1973) [No abstract or article.]

Berendzen, R., Hart. R., "Adriaan van Maanen's Influence of the Island Universe Theory: Part 2," Journal for the History of Astronomy, 4, 73 (1973).

1974

Hetherington, Norriss S., "Edwin Hubble on Adriaan van Maanen's Internal Motions in Spiral Nebulae," Isis, 65, 390-393 (1974) [Added 12 Apr 2007.]

1979

Faber, S. M., Gallagher, J. S., " Masses and Mass-to-Light Ratios of Galaxies," Annu. Rev. Astron. Astrophys. 17, 135-187 (1979).
___

Sulentic, Jack W., Arp, Halton, and Lorre, Jean, "Some Properties of the Knots in the M87 Jet," ApJ, 233, 44-55 (1979)
    Photographs taken in 1956 by Baade show the knots in the jet of M87 to be polarized. In 1978, these plates were repeated under the conditions as identical as possible. A careful comparison indicates that the polarization and intensity of the knots have changed in the 22 year interval. . . . [p. 49]
    ii) Proper Motion in the Jet - Measurements were made of the separation of knot A from the nucleus of M87 in order to see if the knots had shown detectable radial motion over the 22 year time scale. . . .
    [The investigation seems to have evolved into seeing whether or not there was a measurable change in the angular distance between knots A and B in the jet. No quantitative result for proper motion, null or otherwise, for knot A with respect to the nucleus was published.]
    No evidence of a separation change [between knot A and B] was found. . . . [p. 49]

1980

Rohlfs, K. and Kreitschmann, "A Two Component Mass Model for M81 (NGC 3031)," A&A, 87, 175-182 (1980)
    By combining radial velocity data of optical and radio measurements with resolution ranging from a few arc seconds to 9' a well determined rotation curve of M81 has been compiled that shows rather clearly two maxima located at R=1kpc and R=6.5kpc. [The rotation curve is shown on page 176 of ref.] ...
    Unfortunately the distance to M81 is still not well determined, we will adopt here the usual value of D=3.25 Mpc (Tammann and Sandage, 1968) resulting in a scale of 0.945 kpc/arcmin. [p.175] [A comparison of the details of the two maxima above will be made with van Maanen's internal motions for M81.]

1984

Berendzen, Richard; Seeley, Daniel, Man Discovers the Galaxies, Columbia University Press (1984) - Key words and phrases: Slipher, spiral nebulae, Kapteyn, van Maanen, Maanen, globular clusters, Shapley, proper motions, nebulae, Mt. Wilson, Lundmark, radial velocites, Trumpler, internal motions, Cepheids, Edwin Hubble, Albert Einstein, Harlow Shapley, Huntington Library, United States - Keywords are searchable online at Google Book Search. - [Added 12 Apr 2007.]

Smith, Robert W., "The Expanding Universe. Astronomy's 'Great Debate' 1900-1931," 4S Review, 2, 15-17 (1984) - Available online through JSTOR. [Added 12 Apr 2007.]

1988

Van den Bergh, Sidney, "Novae, Supernovae, and the Island Universe Hypothesis," PASP, 100, 8 (1988)

1991

Brashear, Ronald W., Hetherington, Norriss S., "The Hubble-van Maanen conflict over internal motions in spiral nebulae: yet more information on an already old topic," Vistas in Astronomy, 34, 415-423 (1991) [Added 12 Apr 2007.]

1992

Hetherington, N., and Brashear, R., "Walter S. Adams and the Imposed Settlement Between Edwin Hubble and Adriaan van Maanen," Journal for the History of Astronomy, 23, 53-56 (1992) - [See the 1935 Hubble and van Maanen entries above.]

1994

Kroupa, P., Röser, S., and Bastian, U., "On the motion of the Magellanic Clouds," MNRAS, 266, 412-420 (1994) - We have measured the proper motion of the Large and Small Magellanic Clouds using Magellanic Cloud stars in the PPM Catalogue, and obtain mu = 1.7 +/- 0.9 mas/yr for the LMC. [Added 27 Jul 2006.]

Jones, B.F., Klemola, A.R., & Lin, D.N.C., "Proper Motion of the Large Magellanic Cloud and the mass of the galaxy. 1: Observational Results," AJ, 107, 1333-1337 (1994)
    We have measured the proper motion of the Large Magellanic Cloud (LMC) using 21 plates taken with the Cerro-Tolodo Inter-American Observatory (CTIO) 4 m telescope and covering an epoch span of 14 yr. The mean absolute proper motion of the LMC stars in our region is mu_alpha = 0.120 sec +/- 0.029 sec/century, mu_delta = 0.26 sec +/- 0.027 sec/century. [Added 27 Jul 2006.]

1995

Larson, Richard B., "Formation of Small and Large Stellar Systems,"
[pdf] http://www.astro.yale.edu/larson/papers/Petrozavodsk95.pdf
    Current evidence indicates that stars form in a hierarchy of groupings of various sizes, within which binary systems stand out as distinct tightly bound units. The distribution of separations of binaries resembles the internal spatial distributions of stars in larger systems, including massive young star clusters and elliptical galaxies, and this suggests that similar mechanisms may be involved in structuring stellar systems on a wide range of scales. ...

1996

Gingerich, Owen, "The Scale of the Universe: A Curtain Raiser in Four Acts and Four Morals," PASP, 108, 1068-1072 (1996)
    We normally think of Shapley's pioneering work at Mt. Wilson Observatory as delineating the scale of the Milky Way without any quantitative concern for the spiral nebula. It may therefore be a surprise to learn that in 1917 he proposed in the PASP, on the basis of observed novae, that M31, the Andromeda nebula, was at least a million light years away (Shapley 1917). What happened? Why did he retreat so quickly from his published opinion? [Details are summarized.] [p. 1070]
    Is there a moral here? Shapley did not have a clue then about supernovae, interstellar absorption, or the distinction between Population I and Population II cepheids, . . .  The moral, with its warning to today's debaters, I draw from Shakespeare:

    In the annals of modern science, the publication date, or the date of presentation to some august body, is generally used to set priorities and time tables for significant discoveries.   . . . Consequently, we tend to date Hubble's great discovery of cepheids in M31 to 1925, to his formal announcement, in absentia, in Washington at the joint meeting of the AAS and the AAAS on New Year's Day of that year. As Allan Sandage (1961, pp. 4-5) put it in the introduction to The Hubble Atlas of Galaxies,
    "The announcement of Hubble's discovery was dramatic... When Hubble's paper had been read, the entire Society knew that the [great] debate had come to an end, that the island-universe concept of the distribution of matter in space had been proved, and that an era of enlightenment in cosmology had begun." . . .
    But as Richard Berendzen and Michael Hoskins (1971) have written, any account of an instantaneous, overnight resolution of a controversy arouses the suspicion of the historian. . . . [A summary of Hubble's earlier disclosures to his colleagues, and their reactions to the news is given.]
___

Sulentic, Jack, and Smith, Brett, "A Fresh Look at Discordant Redshift Galaxies in Compact Groups," Astrophys. Space Sci., 244,23-28 (1996)

1997

Holmberg, Gustav, Astronomy in Sweden 1860-1940. Uppsala Newsletter: History of Science, 26, (1997).     Offers a commentary on Lundmark's work on spiral nebulae in Sweden. (Comments are in the fourth and third paragraphs from the end.)

1998

Arp, Halton C., Seeing Red: Redshifts, Cosmology and Academic Science, Apeiron, Montreal (1998). Available at: Amazon.com.

2002

___

Duerbeck, H.W., "Extragalactic Research in Europe and the United States in the Early 20th Century," AN, 323, 534-537 (2002)
    While the theoretical foundations of modern relativistic cosmology were laid, to a large extent, by European researchers like Einstein, de Sitter, Friedmann, Lemaître, and others, observational cosmology was (and to a large extent, still is) dominated by US astronomers, working at Lick and Mt. Wilson observatories. From today's viewpoint, Hubble appears to dwarf all his - national and international - peers. However, Keeler and Curtis, Fath and Slipher carried out pioneering work in the US, as did Wolf, Wirtz, Lundmark, de Sitter in Europe, . . .   European extragalactic research during the early 20th century is outlined and compared with studies in the United States. Reasons for the small impact of European research are a mixture of deliberate and accidental neglect and suppression, as well as the lack of technical and organizational infrastructure, which was especially noticeable after World War I. [Abstract © 2002: Astronomische Nachrichten]

2005

Brunthaler, A., Reid, M.J., Falcke, H., Greenhill, L.J., Henkel, C., The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33), Science, 307, 1440-1443 (2005) Sciencemag Abstract - Article [PDF]

These researchers seem to be working under the assumption that the internal motions in M33 behave more or less homogeneously (similar to that expected for a semi-rigid disk) and that rotational velocity, as a function of distance from the center of the disk, can be approximated by a smooth mathematical function. According to van Maanen, the motions could more likely be represented by spiraling river-like streams with regions of stagnation between the spiral elements. Brunthaler's team studied maser regions which do not coorespond to any regions that van Maanen evaluated astrometrically. The team did measure internal motions but these were on the order of 1000 times less than those reported by van Maanen and they were in the opposite direction.

See the author's article Messier 33 Internal Motions (under construction) which compares recent findings versus those of van Mannen. [2005 entries were added on 07 Feb 2007.]

2006

Shin-Yi Lin, Nagayoshi Ohashi, Jeremy Lim, Paul T.P. Ho, Misato Fukagawa and Motohida Tamura, "Possible Molecular Spiral Arms in the Protoplanetary Disk of AB Aurigae," ApJ, 645, 1297-1304 (2006) - Abstract.

Circumstellar dust disk (size 144 x 100 AU) exhibits a complex spiral arms structure. Rotating gas disk (530 x 330 AU) shows maximum rotational velocity of 2.8 km/sec at 450 AU. (Rotation period would be on the order of 760 years.) [Added 26 Dec 2007.]

2012

Evidence that Supported Doubts that Spiral Nebulae are Separate Galaxies - Center for History of Physics - AIP.

The Space Motion of Leo I: Hubble Space Telescope Proper Motion and Implied Orbit arXiv.org>astro-ph> arXiv:1210.6039 [Added 08 Dec 2012]