octant

Benjamin Martin, artist

1704–1782

octant, mid 1700s

Where object was made: England, United Kingdom

Material/technique: mahogany; brass; ivory

Credit line: Museum purchase: Friends of the Art Museum and Helen Foresman Spencer Art Acquisition Fund

Accession number: 2011.0040

On display: Simons Gallery

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Collection Cards: STEM

How would you navigate across an ocean without a computer? Sailors in the 1700s used an octant. The name octant comes from the Latin word for an eighth. The arc at the side of the tool is an eighth of a circle. Sailors would hold the octant at eye level and calculate the angle between a point on the horizon and a point in the sky. Once they knew that angle, they could determine their latitude and cross an ocean by traveling west to east, or east to west. Latitude is the distance north or south from the equator. Using the octant, sailors could sail straight along a certain latitude and not go off course by veering north or south.

What tools do you use for traveling? How do you find your way from one place to another? For example, do you use a GPS, maps, or landmarks?

Soundings: Making Culture at Sea

The octant is a navigational device that measures the angle between two objects, usually the sun, moon, or the North Star, and the horizon. Tools like this were the 18th-century equivalent of GPS for calculating one’s position at sea but required mathematical knowledge and technical skill to use. The expertise of makers like Benjamin Martin, who crafted nautical instruments using such refined materials as mahogany, brass, and ivory, was essential to the expanding maritime culture of the period.

Empire of Things

The octant was a navigational device popular in the 18th and 19th centuries. It measures the angle between two objects, usually a celestial object like the sun, moon, or Polaris (the North Star), and the horizon. Recording the altitude or lunar distance between two objects would allow a ship to determine its latitude or find its position on a nautical chart. This device serves as a reminder of the mathematical calculations and technological innovations that were necessary to efficiently navigate the seas and connect the globe as colonial empires grew and expanded from the 17th century through the 19th century.