Sextant

Sextant

Exploration, navigation, technology

This is an illustration of a sextant including a diagram of the image in the sight when used. It was a navigational instrument developed in the mid-18th century, and is still in use today as a back-up in situations where electricity is not available. The sextant was primarily used to establish one's latitude by determining the angle between a star (Polaris, the sun, etc.) and the horizon. Another key function was that it allowed a sailor to determine the present longitude, which had been a navigational problem for centuries. The sextant could be used to measure the angle between the moon and a star so that Greenwich time (takes advantage of the relationship betweem time and longitude) could be calculated. Longitude was calculated via the comparison of Greenwich time and the present local time (calculated using the altitude of a star). Nautical almanacs, including various related data, were published and circulated beginning in the mid-18th century allowing for quicker calculations and contributed to the establishment of the universally accepted Greenwich meridian. The development of both the octant and sextant in the 18th century rendered older navigational instruments obsolete.

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Wikimedia Commons

Public Domain

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