Re: Distance of spiral nebulae

From: Jonathan Clarke (
Date: Thu Jan 24 2002 - 17:14:00 EST

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    Glenn Morton wrote:

    > I find so many parallels between what Whewell did and what RTB is doing with
    > anthropology that it utterly amazes me.

    You are repeating this assertion without any evidence. I really think your projecting
    your quite legitimate concerns about RTB onto a different person and era.

    > >There were two issues: 1) whether the faint points of light in the spiral
    > >nebulae were stars and 2) how far they were.
    > I wish you would support this with documentation. The great debate site
    > says nothing that I can find about whether the points of light in the
    > galaxies were stars or not. It seems that everyone beleived they were stars,
    > but disagreed on their absolute magnitudes, which affects the view of how
    > far away they are: From the great debate web site I will post what they say
    > were the issues, and I wish someone would point out where the issue of
    > whether the points-of-light-in-the-nebula-are-stars issue appears.

    You are changing the subject, which is Whewell, not the great debate. The only
    significance of the great debate is that is shows that even in 1920 there was dissent
    on what spiral nebulae were composed of and how far away they were. Therefore we
    should go easy on Whewell for not accepting observations made only a few years before
    his book.

    > >>>Shapley and Curtis disagreed to some extent on at least 14 astronomical
    > issues. These are presented in the following paragraphs in roughly the order
    > in which they occur in the printed texts (Shapley 1921, Curtis 1921), which
    > is neither in order of importance nor according to any other pattern a
    > modern reviewer would be likely to choose. According to the actual texts
    > reproduced by Hoskin (1976), no other additional scientific points were made
    > during the main talks, though some may have arisen during Russell's rebuttal
    > or other parts of the discussion, no record of which has been preserved.
    > Each paragraph indicated an issue, what each disputant thought (or anyhow
    > wrote or said), what we think now and sometimes why, and who should be
    > counted the winner on each issue.

    Shapely while accepting that the spiral nebulae were extra galactic did not accept
    their their stellar nature. In his paper 1921 paper that came out of the great debate
    he wrote:

    "It seems to me that the evidence, other than the admittedly critical tests depending
    on the size of the
    galaxy, is opposed to the view that the spirals are galaxies of stars comparable with
    our own. In fact,
    there appears as yet no reason for modifying the tentative hypothesis that the spirals
    are not
    composed of typical stars at all, but are truly nebulous objects. Three very recent
    results are, I
    believe, distinctly serious for the theory that spiral nebulae are comparable galaxies
    - (1) Seares'
    deduction that none of the known spiral nebulae has a surface brightness as small as
    that of our
    galaxy; (2) Reynold's study of the distribution of light and color in typical spirals,
    from which he
    concludes they cannot be stellar systems; and (3) van Maanen's recent measures of
    rotation in the
    spiral M 33, corroborating his earlier work on Messier 101 and 81, and indicating that
    these bright
    spirals cannot reasonably be the excessive distant objects required by the theory. "

    It would be interesting to know when, if ever, Shapley accepted that the spiral nebulae
    were galaxies. it is ironic that both Curtis and Shapley agreed that if the galaxy was
    as large as Shapley said it was then this made the number of stars represented by
    spiral galaxies impossibly large. even their imaginations baulked at this number.
    This seems to be the reason why Curtis wanted a smaller galaxy, so that the spiral
    galaxies would not become impossibly huge.

    Unless we get back to the real point, which is Whewell and his contemporaries, I have
    nothing more to say on the subject. The only point I had in mentioning the great debate
    was that almost 70 years after Whewell's book there were still legitimate reasons to
    reject their galactic nature. You may have the last word on the great debate.



    > 1. Resolved F, G, and K stars in globular clusters. Shapley believed they
    > were giants like local F-K giants, with absolute magnitudes near -3, placing
    > average globular clusters 10-30 kpc from us. Curtis said they were like the
    > commonest sorts of stars around us, F-K dwarfs, with average visual
    > magnitudes of about +7, putting the clusters at a kpc or two. As became
    > unambiguously clear when the first 200" color-magnitude diagrams of
    > globulars reached the main sequence turn-off (e.g. Sandage 1953), Shapley
    > was essentially right on this one.

    > 2. B stars in globular clusters. Shapley said they should have absolute
    > magnitudes near 0, like nearby main sequence late B and early A stars.
    > Curtis responded that something very strange must be going on, since the
    > brightest blue stars in the solar neighborhood are brighter than the
    > brightest red stars, while the opposite is true in the clusters. It took the
    > insight of Walter Baade and his data gathered during the black outs of WWII
    > to sort this one out, with the concept of two stellar populations. Each of
    > the speakers was right about the particular point he emphasized.

    > 3. Cepheids as distance indicators. Shapley used the relative
    > period-luminosity relation found in the Large Magellanic Cloud with its zero
    > point calibrated on a handful of Milky Way disk examples using statistical
    > parallax. He noted that the nearby Cepheids of the cluster type (that is, RR
    > Lyrae stars) are high velocity objects and must not be used for the
    > calibration. Curtis responded that there was no evidence for a
    > period-luminosity relation in the Milky Way, and that a larger sample,
    > including some stars with geometric parallax measurements, even ruled it
    > out. This was the point on which he said most firmly "more data are needed."
    > When they came, Milky Way Cepheids did display a P-L relation, based both on
    > secular parallaxes (or statistical) and on open cluster members. But the
    > zero point was offset from the globular cluster one by more than a
    > magnitude. This also was the work of Baade, who knew something was wrong the
    > day (or rather night) he turned the 200" toward Andromeda and saw no RR
    > Lyrae stars. Curtis was right about "more data" but wrong about what they
    > would show -- he had placed too much faith in tiny geometric parallaxes,
    > though he had more sense (paragraph 14) than to be misled by tiny proper
    > motions. Shapley was right that Cepheids are generally good distance
    > indicators.
    > 4. Spectroscopic parallaxes in general. Shapley believed these could be
    > trusted as long as you could see any of the line ratios indicative of giant
    > surface gravities in nearby stars. Curtis believed they should be trusted
    > only in the region of less than 100 pc where they had been calibrated.
    > Errors and omissions expected (like some high latitude B stars), Shapley was
    > right on this, though one shudders to think of the faith of eye required to
    > see luminosity indicators like the ratio of 4215 (Sr II) to 4454 (Ca I) in
    > spectra of individual globular cluster giants taken before 1920.
    > 5. Interpretation of star counts. Curtis said, correctly, that star counts,
    > straightforwardly interpreted, require a small Milky Way. His idea that
    > spiral nebula dust existed as a ring around the stellar disk prevented him
    > from suggesting absorption as relevant to the problem. Shapley did not
    > address the issue, presumably because his use of globular clusters had
    > already committed him to the "negligible absorption" camp, and he could,
    > therefore, say nothing to rebut the point. Robert Trumpler (1930), by
    > correlating apparent diameters of open star clusters with their apparent
    > brightnesses revealed the importance of interstellar absorption (though
    > Jesse Greenstein and others had come very close to discovering it earlier).
    > 6. Stellar evolution theory. Shapley claimed that if and only if the
    > globular clusters were put at large distances would their stars fir the
    > Russell giant and dwarf theory and Eddington's models of gaseous giants.
    > Curtis opined that spiral nebulae as a phase of stellar evolution didn't fit
    > anywhere in any reasonable theory (remember protostellar nebulae were Out
    > for solar system formation and encounters were In that year, and Jeans' idea
    > that they were places where new stuff was pouring into the galaxy from
    > Elsewhere had yet to be espoused and modified by Victor Ambarsumyan and
    > others). While both points were true enough, we have to count Curtis the
    > winner on this one, since we no longer adhere to the giant and dwarf theory!
    > 7. Distribution of spiral nebulae on the sky. Shapley doesn't really mention
    > this, but for a "single system" man, it was no more unreasonable for spirals
    > to avoid the galactic plane than for OB stars to favor it. Curtis was forced
    > to deal with the problem and concluded that it was "neither impossible nor
    > implausible" for the Milky Way to have an occulting ring around it, as many
    > edge-on spirals seem to, so that we would not be able to see nebulae in the
    > plane. Curtis was closer to the truth than Shapley, but missed the critical
    > point that stars and absorbing material are mixed together.
    > 8. Nova brightness at maximum light. Both speakers agreed that "new stars"
    > had been seen in the Milky Way and in several spiral nebulae. Shapley felt
    > strongly that the implied real brightnesses would be totally ridiculous if
    > the spirals were separate galaxies. Curtis said that, for four events with
    > estimated distances in the Milky Way and a handful of novae in spirals, peak
    > luminosity would be the same, provided the Milky Way had his preferred small
    > size and the spirals were separate systems of similar physical diameter. He
    > agreed that S Andromeda in 1885 was much brighter than this general run of
    > events, said that Tycho's nova probably had been too, and concluded "a
    > division into two classes is not impossible." One of the participants in our
    > modern debate presumably feels the same way about the gamma ray bursters.
    > Notice that Curtis was willing to trust a calibration based on four examples
    > when he liked the answer, but not for the Cepheids, where he didn't. Two
    > classes was, of course, the solution. Lundmark (1920) hinted at it, and
    > Baade and Zwicky (1934) said it firmly from December 1933 onward, dubbing
    > the brighter class super-novae (the hyphen disappeared the year Hale died;
    > not causal). Curtis gets the points for this topic.
    > 9. Nova mechanisms. Shapley suggested, seemingly with a straight face, that
    > both the star and the nebulosity had existed to begin with, and that nebulae
    > (with their large velocities) overtook and enveloped stars, producing nova
    > events. He claimed to get the right rate of a few per year in the Milky Way
    > from the numbers of stars and nebulae in his model universe. Curtis
    > countered that the proposed mechanism would yield a rate of 1 per 500 years
    > in Andromeda, where several had already been caught in the last 20 years.
    > Once again, Curtis 1, Shapley 0.
    > 10. The large, positive average velocities of the spiral nebulae. Shapley
    > suggested the cause might be repulsion by radiation pressure from the Milky
    > Way (a mechanism Russell showed to fail by many orders of magnitude the same
    > year). Curtis simply proposed that large (mostly) positive wavelength shifts
    > might somehow be intrinsic to the nebulae, and a large velocity also
    > characteristic of the Milky Way. There are cases where "I haven't a clue" is
    > the correct answer. It took the combined force of observations by Hubble,
    > Milton Humason, and others and theoretical advances by Einstein, Alexander
    > Friedmann, and others to come up with expansion of the universe as the
    > explanation. Curtis over Shapley again, though perhaps not full marks.
    > Incidentally, in case I forgot to mention it elsewhere, Einstein did not
    > attend the 1920 debate, pace Florence (1994) and could not have, being still
    > in Europe.
    > 11. Properties of Galaxies, I. Shapley pointed out that the observed central
    > surface brightnesses of spiral nebulae are much larger than anything seen in
    > the Milky Way and the radial distributions of colors and surface
    > brightnesses are different. Curtis remained silent on the issue. The answer,
    > of course, is absorption and reddening, so Shapley was right about the data,
    > but wrong about the interpretation. Love-love.
    > 12. Properties of Galaxies II. According to Curtis, spiral nebulae have
    > colors and line spectra a lot like those of star clusters, implying that the
    > nebulae are mostly large assemblages of stars. Shapley did not mention this,
    > and Curtis was right.
    > 13. Central location of the sun. Shapley claimed this was an illusion,
    > caused by the local star cloud now called Gould's belt. Curtis said it was
    > God's own truth, and that our location kept us from readily seeing our own
    > spiral arms. Once again, dust is an important part of the picture, but
    > Shapley was nearly right.
    > 14. Rotational proper motions of spirals as measured by van Maanen. Shapley
    > said these were "fatal to the comparable galaxy theory." Curtis fully
    > agreed, but said that you should never trust a proper motion of less than
    > 0.1/yr for fuzzy things measured from a base line of 25 years or less. A
    > round of applause for Curtis and sympathy for Shapley, who said later that
    > van Maanen was his friend, so of course he believed him.<<<
    > Everyone seemed to accept the fact that they were stars by 1920 and had to
    > have been determined by Rosse's telescope.
    > >Until the distance to spiral nebulae could be resolved the
    > >question became how
    > >far these spiral nebulae were. Were they galaxies similar in size
    > >to ours or
    > >clusters of faint stars. Their distance could not be resolved
    > >using the H-R
    > >diagram as the stars were too faint and too close together to resolve
    > >individually using the spectroscope. This is where Henrietta
    > >Leavitt's work on
    > >using Cephid variables proved decisive when applied by Edwin
    > >Hubble to M31 in
    > >1923 (see previous web reference).
    > But the cepheid work was what allowed finally a distance measure. That does
    > not address the issue of whether or not the stars were stars in the nebula.
    > >
    > >Although Parsons was correct, his observations were controversial and not
    > >vindicated for 70 years. While celebrating Parson's vision we
    > >should avoid Whig
    > >views of history while. Whewell was wrong, but was he right for
    > >good or bad
    > >reasons. We know he originally was sympathetic to the purality of
    > >worlds. Did
    > >he change his ideas because of his theology changed or because of
    > >scientific
    > >evidence?
    > Michael Ruse beleives he changed because of the threat of evolution. That is
    > in the preface to the book I am reading. Ruse writes:
    > "First was Whewell's own personal change of status and consequent
    > redirection of interest. By the 1850s, he was no longer a mere tutor,
    > textbook writer, and second-class researcher, but an important figure of
    > influence and authority with responsibility for the moral and spiritual
    > welfare of young people. Whewell had been writing more on ethics and
    > standards of right behavior, and was much interested in educating the young.
    > As an ordained member of a church institution, Whewell was pushed more
    > toward issues of revealed religion rather than the purely natural variety.
    > Immortal souls were at stake, including his own (as Whewell was growing
    > older) and that of his wife (who was dying). For Whewell, the direct
    > teachings and consolations of Christianity loomed larger.
    > "The second factor changing Whewell's views was that, in the 1840s, Whewell
    > and his circle had been shocked and battered by the anonymous publication of
    > the evolutionary tract, Vestiges of the Natural History of Creation, by the
    > Scottish publisher Robert Chambers." Ruse Introduction in Whewell p. 12
    > If you could get his earlier work it would make an interesting
    > >comparison. But seeing that people like Robert Chambers and
    > >Christian Huygens
    > >were Christians and Thomas Chambers a "woolly" Anglican with
    > >deistic tendencies,
    > >the connection often made between belief in a plurality of
    > >inhabited worlds or
    > >of island universes and atheism, seems weak. But it would be a
    > >fruitful area of
    > >historical research.
    > I might try to get a copy of Chambers earlier work.

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