RE: Distance of spiral nebulae

From: Glenn Morton (
Date: Thu Jan 24 2002 - 09:24:45 EST

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

    >-----Original Message-----
    >From: []On
    >Behalf Of Jonathan Clarke
    >Sent: Wednesday, January 23, 2002 2:29 PM
    >Cc: Asa@Calvin. Edu
    >Subject: Distance of spiral nebulae
    >Hi Glenn
    >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.

    >>>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.

    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

    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

    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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