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    Re: transit of venus 1769
    From: George Huxtable
    Date: 2006 May 27, 17:41 -0500

    Coralline Algae wrote some nice words about the book  "The Ship", with
    which I had a marginal involvement. Yes, it was produced to a high
    quality, as are many books from the BBC. I only wish the same could be
    said about the TV series on which it was based.

    " I did not mean to imply that the
    atmosphere of venus and the blackdrop were the same effect but that
    than one factor affected the observations."

    Although the effects of Venus' atmosphere were thought by many, over a
    long period, to contribute to the "black drop", it fact there was no
    such observable contribution. The "black drop's causes were entirely

    "It is mentioned in wikipedia, after the 1761 transit of venus was
    observed a russian
    predicted the existence of an atmosphere on venus.

    I have looked up that web page on Lomonosov, and can find no mention
    there of the transit of Venus, or an atmosphere. Of course, Venus does
    indeed have an atmosphere, so in that respect Lomonosov was right, if
    he predicted it. But if he did so on the basis of the "black drop"
    observations, then it must be a classic case of getting the right
    answer for the wrong reasons. If Coralline Algae can provide more
    details about the matter, I would be interested.

    " The work of James Short
    and Thomas Hadley in the analysis from the 1769 observations brought
    size of the AU to within 1 percent of todays figure."

    James Short was an instrument maker, so it would be a bit surprising
    if he were to be involved in serious analysis of the transit results;
    it would be interesting to learn more. I haven't come across Thomas
    Hadley; not the Hadley who invented the octant, that was John. Again,
    it would be good to learn more.

    "One very interesting aspect about all this is that the Board of
    awarded monetary prizes to the widow of Tobias Mayer for his lunar
    and an unsolicited gift to Leonhard Euler for his mathematical works
    used by
    Mayer for the tables in 1765, which was well before the transit
    observations.  Also Nevil Maskelyne began printing an almanac in 1767
    with lunar tables in 1767, so the precise value of the AU was not
    to compile fairly accurate  ephemerides at that time."

    Yes, that deduction is right. The transit of Venus observations were
    intended to produce precise answers for the size of the solar system,
    and thus such matters as the velocity of light and, to an extent, the
    gravitational constant. Scientifically interesting information in
    itself, but having little impact on the prediction of ephemerides;
    only affecting such minor matters as the parallax of the Sun and
    planets. Indeed, because the Earth-Sun distance had such small effects
    in positional astronomy, that in itself explains why that distance was
    so hard to measure.

    Mayer's lunar prediction method was communicated to the Admiralty as
    early as 1755, and provided the basis for trial voyages made by
    Maskelyne for testing the lunar distance method. By the time of
    Mayer's death in 1762 he had significantly improved its accuracy, and
    that formed the basis of the lunar distance tables for the first
    Nautical Almanac, published in 1766 for the year 1767.


    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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