Heliometer

Source: Wikipedia, the free encyclopedia.

Kuffner observatory
(Vienna, Austria)

A heliometer (from Greek ἥλιος hḗlios "sun" and measure) is an instrument originally designed for measuring the variation of the Sun's diameter at different seasons of the year, but applied now to the modern form of the instrument which is capable of much wider use.[1]

Description

Heliometer by Carl Bamberg, Berlin, around 1880/1890. Diameter of the lens 4.2 cm.
Double image of the solar disk

The basic concept is to introduce a split element into a telescope's optical path so as to produce a double image. If one element is moved using a screw

object lens
in half, with one half fixed and the other attached to the micrometer screw and slid along the cut diameter. To measure the diameter of the Sun, for example, the micrometer is first adjusted so that the two images of the solar disk coincide (the "zero" position where the split elements form essentially a single element). The micrometer is then adjusted so that diametrically opposite sides of the two images of the solar disk just touch each other. The difference in the two micrometer readings so obtained is the (angular) diameter of the Sun. Similarly, a precise measurement of the apparent separation between two nearby stars, A and B, is made by first superimposing the two images of the stars and then adjusting the double image so that star A in one image coincides with star B in the other. The difference in the two micrometer readings so obtained is the apparent separation or angular distance between the two stars.

History

The Syrian Arab astronomer Mu'ayyad al-Din al-Urdi, in his book, described a device called "the instrument with the two holes," which he used to measure and observe the apparent diameters of the Sun and the Moon.[2]

The first application of the divided object-glass and the employment of double images in astronomical measures is due to Servington Savery of Shilstone in 1743. Pierre Bouguer, in 1748, originated the true conception of measurement by double image without the auxiliary aid of a filar micrometer, that is by changing the distance between two object-glasses of equal focus.[1]

great refractors of the period, and overcame atmospheric turbulence in measurements compared to a filar micrometer.[5]

Heliometer at Yale College, New Haven, US: c. 1910, built by Repsolds

Notes

  1. ^ a b c  One or more of the preceding sentences incorporates text from a publication now in the public domain: Gill, David (1911). "Heliometer". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 13 (11th ed.). Cambridge University Press. pp. 224–230.
  2. ^ History Of Science And Technology In Islam Fuat Sezgin. 2011.
  3. ISBN 0-03-006228-4
    ..
  4. ^ "Photos". klima-luft.de. Retrieved 16 August 2015.
  5. ^
    ISBN 978-0-8050-7133-7
    .

Further reading

  • Willach, Rolf. "The Heliometer: Instrument for Gauging Distances in Space." Journal of the Antique Telescope Society, number 26, pp. 5–16 (2004).

External links

Look up heliometer in Wiktionary, the free dictionary.
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