page_title: Greenwich 28 inch refractor
section_title: Mounting
hierarchical_section_title: Greenwich 28 inch refractor / Mounting
caption_attribution_description: The great equatorial telescope in the Dome at Greenwich. Wellcome Images Keywords: Telescopes
context_page_description: The Greenwich 28-inch refractor is a telescope at the Royal Observatory, Greenwich, where it was first installed in 1893. It is a 28-inch aperture objective lens telescope, otherwise known as a refractor, and was made by the telescope maker Sir Howard Grubb.
  The achromatic lens was made Grubb from Chance Brothers glass.
  The mounting is older however and dates to the 1850s, having been designed by Royal Observatory director George Airy and the firm Ransomes and Simms. The telescope is noted for its spherical dome which extends beyond the tower, nicknamed the "onion" dome.
  Another name for this telescope is "The Great Equatorial" which it shares with the building, which housed an older but smaller telescope previously.
  The telescope was re-commissioned by Queen Elizabeth II in May 1975 after it was brought back from Herstmonceux in Sussex. It was placed in the renovated original dome at Greenwich for the tricentenntial celebration of the observatory.
context_section_description: The mounting was designed by George Airy in the 1850s, for the older 13-inch refractor, in conjunction with the firm Ransomes and Simms. It is an equatorial design, that allows the telescope to rotate to compensate for the rotation of the Earth; this allows the telescope to stay fixed on certain point in the heavens. The telescope tube is mounted in a latticework of iron, that is mounted on each end on spindle that rest on a stone and metal pier.
  In the 1890s the mount was able to accommodate the 28-inch, and was thus re-used.
  Originally it was rotated by a clockwork drive powered by water, and later in the 20th century this was replaced by electric motor driven system. In 1897 it was said that the clockwork water drive that "the water clock in general drives it with great precision."
caption: Illustration of the older telescope; the 28-inch used the same mount. However, it needed a new dome due to being longer
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