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William Herschel

1738 - 1822

William Herschel

William Herschel is one of the most famous of all astronomers, best remembered for his discovery of Uranus in 1781.

  • Nationality
  • German-British

  • Subject
  • Astronomy, observational

  • Fields
  • Telescope development, planets, music

  • Distinctions
  • Copley Medal, 1781.

  • Posts
  • Court Astronomer, under George III

    Herschel was instrumental in the foundation of the Royal Astronomical Society, and was elected foreign member of the Royal Swedish Academy of Sciences.

  • Publications
  • Catalogue of One Thousand New Nebulae and Clusters of Stars, 1786.

    Catalogue of a Second Thousand New Nebulae and Clusters of Stars, 1789.

    Catalogue of 500 new Nebulae, nebulous Stars, planetary Nebulae, and Clusters of Stars; with Remarks on the Construction of the Heavens, 1802, containing 2,500 objects.

    Account of the Changes that have happened, during the last Twenty-five Years, in the relative Situation of Double-stars; with an Investigation of the Cause to which they are owing, 1803.

    Catalogue of Nebulae, 1820, containing 5,000 objects.

  • Theories
  • Spectrophotometry as a diagnostic tool in astronomy, using prisms to measure the wavelength distribution of stella spectra.

    Discovery of infrared radiation.

    Leading role in founding modern binary star astronomy.

    Proper motion of stars, and used parallax shifts in separation of stars to determine their distance from Earth (putting into practice an idea of Galileo).

    His catalogues formed the basis for the 1888 NGC (New General Catalogue), which is the system still used to name and identify celestial objects.

    Herschel speculated about life on the Moon and other planets.

    Correlation of solar variation and climate. He compared his observation of sunspots, made during the Dalton minimum, with wheat prices.

    Herschel invented the term 'asteroid' (Greek aster = star, eidos = form) for minor planets in orbit around the giant planets.

    Motion of the solar system through space, and disk shape of the Milky Way, but incorrectly assumed the Sun was the centre of the galaxy.

  • Experiments/Discoveries
  • Designed and built a range of powerful telescopes (more than 400 in total), with unprecedented magnification and resolution power.

    Herschel used a microscope to determine that coral, lacking cells, was not a plant.

    Astronomical Observations

    - Rotation period and seasonal polar caps of Mars.

    - The nebulae of the Messier Catalogue were star clusters.

    - Uranus (1781) and two of its moons: Titania and Oberon (1787).

    - Moons of Saturn: Enceladus and Mimas (1789).

    - Rotation period, axial tilt, and seasonal polar caps of Mars.

    - Several hundred binary and multiple star systems.

Herschel telescope
William and Coraline Herschel's 1.26m reflecting telescope, with a focal length of 12m

Born in Hanover, Germany, William Herschel, then 19, went to England in 1755 with his father, who was an oboist in the Hanover Military Band. Herschel's first career was a musician (violin, harpsichord, organ) and composer. He wrote 24 symphonies, among a considerable corpus of works, stil performed today.

He moved to Bath, where he was director of public concerts. His house is now a museum. He was joined there in 1772 by his sister, Caroline, also a famous astronomer.

He developed an interest in mathematics and lenses, and developed his own reflecting telescopes, grinding his own speculum metal primary mirrors, a laborious task. His observations began in 1773, and his astronomical journal in 1774.

Herschel built over 400 telescopes. The most famous is the 12m reflecting telescope, with a 1.26m primary mirror and 12m focal length.

The Herschelian telescope is a telescope without a redirecting mirror close to the focal point, thereby avoiding loss of light intensity due to the low reflectivity of mirrors of the time.

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