first segmented mirror

    Caption: Guido Horn d'Arturo (1879--1967) and the world's first working segmented mirror which he built in 1952. The Horn d'Arturo segmented mirror telescope had 61 hexagonal segment mirrors and a 1.8-meter diameter (Wikipedia: Guido Horn d'Arturo: Segmented mirror telescope). It was a zenith telescope, and so it always pointed to zenith and was NEVER slewed (Wikipedia: Guido Horn d'Arturo: Segmented mirror telescope). Since it did NOT slew, the segments were held rigidly in place and did NOT use active optics to hold the segments to the precise parabolic reflector shape. The individual segments were, in fact, spherical mirrors, but they were arranged to give an overall parabolic reflector shape (Wikipedia: Guido Horn d'Arturo: Segmented mirror telescope)???.

    JWST Features:

    1. Image 2 Caption: The Horn d'Arturo segmented mirror telescope is the remote ancestor of the segmented mirror of the mighty James Webb Space Telescope (JWST, 2021--2041?, diameter = 6.5 m, 18 segment mirrors of gold-plated beryllium, Cassegrain reflector).

    2. Monolithic mirrors for the primary mirrors of reflector telescopes CANNOT be built larger than ∼ 8 meters in diameter since they hard to build and they tend to sag under their own weight (Wikipedia: Segmented mirror: Application).

    3. For larger primaries, the solution was segments that when assembled can make the aforesaid larger primaries. To hold their precise optical shape and for adaptive optics, the segments have to be computer contolled (i.e., make use of active optics), except for zenith telescopes like the Horn d'Arturo segmented mirror telescope as discussed above.

    4. The segments can have any shape and do NOT to be contiguous NOR nearly contiguous. In fact, hexagonal and circular segments seem to be the only ones used (Wikimedia Commons: File:Comparison optical telescope primary mirrors.svg).

    5. For more details about segmented mirror, see Telescope file: telescope_segmented_mirror_4.html which may be this file in which case see below.

    Images:
    1. Credit/Permission: © User:Krishnavedala, 2014 / CC BY-SA 3.0.
      Image link: Wikimedia Commons: File:Specchio-tasselli-horn.jpg.
    2. Credit/Permission: NASA, 2016 (uploaded to Wikimedia Commons by User:Astrofreak92, 2016) / Public domain.
      Image link: Wikimedia Commons: File:JWST Full Mirror.jpg.
    3. Credit/Permission: © David Jeffery, 2024 / Own work.
      Image link: Itself.
    4. Credit/Permission: © David Jeffery, 2024 / Own work.
      Image link: Itself.
    5. Credit/Permission: © David Jeffery, 2024 / Own work.
      Image link: Itself.
    Local file: local link: telescope_segmented_mirror.html.
    Extended File: Telescope file: telescope_segmented_mirror_4.html.
    File: Telescope file: telescope_segmented_mirror.html.