Hadley's Octant

Hadley's Octant

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Technique and Dimensions:

Diameter 30 cm


Second floor, Room 15 (inv. no. 1796)

Object Type:

Scientific instrument


The octant is a reflective instrument used to measure the height from the horizon of a reference star (the Sun or the Polar Star), in order to determine the latitude of a given point on the earth's surface. Generally it is formed of a frame shaped like the section of a circle  frame, with graduated measurements along the lower edge and an opening of about 45 ° (an eighth of an angle of turn).

Hadley's octant takes the form of the model exhibited after 1760. Octants were not only slowly adopted in Italy because they were very expensive.