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Thread: Question on publication of Alpha Centuari distance from Earth

  1. #1
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    Question on publication of Alpha Centuari distance from Earth

    Hi folks

    Does anyone know exactly when and how/where Henderson published his measurement of the parallax to Alpha Centauri? At present all I can find is that it was in February 1839.

    ""In early 1838, Bessel began his 61 Cygni observations using the 18th Century 11.6cm. equatorial telescopic device known as a heliometer, which has a split objective. By November 1838, he found an accurate parallax of 0.314±0.014 arcsec. and the distance of 10.4±0.95 ly. This fairly precise result was published in December 1838. Having no personal doubt on his methodology, history records Bessel as the discoverer of the first stellar distance. Soon after seeing Bessel’s result, Henderson’s doubt was quashed and he published his results in February 1839. (Here Henderson’ remains a pertinent warning of the “cut-throat” world of both science and professional astronomy “publish or perish.”) However, worrying about “divvying the spoils” in finding these three results cannot reduce the notable importance of these discoveries because 1838 marks the first steps in finding distances beyond the realm of our Solar System.""

    http://www.southastrodel.com/PageAlphaCen005.htm

    Thanks

  2. #2
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    January 1839, via a communication to the Royal Astronomical Society.
    On the Parallax of α Centauri. Monthly Notices of the Royal Astronomical Society, Volume 4, Issue 19, 11 January 1839, pp168-9.

    Grant Hutchison
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  3. #3
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    Thanks for the link. I have one question I don't see a distance mentioned there just the parallax - is it presume that the reader would be able to calculate the distance from that? (I certainly cannot) I was hoping to see in that report what unit of measure they used to announce the distance. I believe at this time the term 'light years' was no in use.

    Would you know anything about that?. Now that was January 1839 was there another report in February of that year? I looked thru the remaining reports (42) in your source but didn't find anything that spoke about a declaration of distance.

    I appreciate your assistance in this matter.

  4. #4
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    It is just trig to do the conversion, see https://en.m.wikipedia.org/wiki/Para...ce_measurement for a guide. A conversion for small angles is distance in parsecs is 1/parallax in arcsec. So 1/0.314 is about 3.18pc or 10.4ly.

    Not sure what units they would have converted to then. Parsec came later, in the next century.

  5. #5
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    If you look at Bessel's original communication (A letter from Professor Bessel to Sir J. Herschel, Bart., dated Konigsberg, Oct. 23, 1838. Monthly Notices of the Royal Astronomical Society, Volume 4, Issue 17, 9 November 1838, pp 152-61), you'll see that the discussion is generally couched in terms of the thing measured, parallactic seconds, and any astronomer would be able to work out the distance. Bessel gives his derived distance as "657700 mean distances of the earth from the sun : light employs 10.3 years to traverse this distance". So we have both astronomical units and light years, but without their modern names.

    Grant Hutchison
    Blog

    Note:
    During life, we all develop attitudes and strategies to make our interactions with others more pleasant and useful. If I mention mine here, those comments can apply only to myself, my experiences and my situation. Such remarks cannot and should not be construed as dismissing, denigrating, devaluing or criticizing any different attitudes and strategies that other people have evolved as a result of their different situation and different experiences.

  6. #6
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    Many thanks for finding that letter. Explained! Now if I can only figure out how to get two gentlemen in 1839 to discuss that intelligently!
    Last edited by Hans; 2018-Apr-17 at 04:04 PM.

  7. #7
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    "657700 mean distances of the earth from the sun : light employs 10.3 years to traverse this distance"
    That is an error of over two to one. How did they get any result with such an error?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  8. #8
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    Quote Originally Posted by Tom Mazanec View Post
    "657700 mean distances of the earth from the sun : light employs 10.3 years to traverse this distance"
    That is an error of over two to one. How did they get any result with such an error?
    That was for 61 Cygni, not Alpha Centauri.

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