Types of Sextants

A sextant is a device for celestial navigation designed to measure the angle between two objects, usually between a celestial body and the horizon. The purpose of this procedure, called "sighting" an object, is to determine latitude and longitude and thus geographic location. Various types of sextants exist. Some use the celestial bodies for reference using the vertical plane, while others only use terrestrial objects and measure along the horizontal plane.

  1. Navigator Sextant

    • A navigator sextant is the most used type of sextant. A basic sextant consists of an eyepiece, mirrors, a movable arm and a measured scale. Some are contained within an enclosing box, aiding the device's transportability and protecting it from harm. Mariners at sea used navigator sextants as did overland navigators, such as traders for the Hudson's Bay Company.

    Sounding Sextant

    • The sounding sextant measures positions horizontally rather than vertically and is for hydrographical surveying. The sounding sextant measures angles between terrestrial objects to fix the position at where a sounding was carried out, and thus has no need for shades. The telescope that was attached to the sounding sextant was usually a Galilean type, of two to five magnifications. Most sounding sextants were designed to be held on the right side, and had their legs located on the same side as the handle.

    Surveying Sextant

    • The surveying sextant was used exclusively on land and combined a sextant together with a leveling stand to fix its position. Primarily used to take astronomical readings to reveal latitude, it could also turn on a horizontal plane to measure across bays, rivers and other poorly accessible geographic regions.

    Box Sextant

    • The box sextant, also sometimes called the pocket sextant, is a hand-held sextant designed to determine the angles between two given positions. Measuring approximately 3 inches in length, versions were designed with or without a telescope. The box sextant is designed to only measure angles that are within the instrument's plane; thus, if the stations are at different levels, then the angle given will be the direct angle between them.