A quadrant is a basic tool that calculates the latitude and the altitude of a celestial body. A quadrant is a scientific or astronomical instrument with a graded arc covering a quarter of a complete circle or 90 degrees. Astronomical quadrants were mainly used to assume the altitude of a celestial body above the horizon. The geographical latitude of an observer might be determined using the meridian altitudes of the sunrise or a bright star, or the observer could know the time by measuring an altitude that was not too close to the meridian direction if the latitude is known. The ‘plinth’ described by Claudius Ptolemy in his Almagest around 150 A.D. was one of the earliest forms of a quadrant. Let us now know about the history of the quadrant, and which scientist invented the quadrant?

History of the Quadrant

•   Ptolemy’s Almagest, written around AD 150, has one of the oldest accounts of a quadrant.
•   In the Middle Ages, Islamic astronomers improved on these concepts and created quadrants in observatories around the Middle East. Originally, these quadrants were enormous and immovable. They could be turned around in any direction to determine the height and latitude of any celestial body.
•   The awareness of these instruments extended throughout Europe during the Middle Ages. Jacob ben Machir ibn Tibbon, a Jewish astronomer in the 13th century, was instrumental in furthering research about quadrants.
•   Diogo Gomes used the quadrant to travel at sea for the first time in 1461. To determine their latitude, sailors first measured the height of Polaris.
•   Edmund Gunter, an English mathematician, improved the quadrant in 1618 with an innovation that became recognised as the Gunter quadrant. This pocket-sized quadrant was groundbreaking because it was etched with projections of the equator, the tropics, the horizon, and the ecliptic.

Types of Quadrant

Gunners quadrant

The depth angle of the altitude of a cannon or mortar’s gun barrel is measured with Gunner’s quadrant. This is a sort of clinometer that is used to ensure that the firing elevation and synchronisation of fire control-equipped weapons are proper. The invention of Gunter’s quadrant dates from 1623.

Islamic quadrant

Following are the types of Islamic quadrants

1. Sine quadrant- A form of quadrant employed by mediaeval Arabic astronomers was the sine quadrant. The equipment was used to calculate the actual positions of any celestial body at any moment, tell time, identify directions, or measure celestial angles.
2. Universal quadrant- It was used to solve astronomical problems involving latitude.
3. Horary quadrant- The sun was utilised to determine the time using the horary quadrant.
4. Astrolabe quadrant-  The astrolabe/almucantar quadrant is a popular alternative to the astrolabe.

Geometric quadrant:

The geometric quadrant is commonly made of brass or wood in a quarter-circle panel. Geometric quadrants for nautical navigation date back to 1460. These quadrants had target latitudes instead of degrees.

Back observation quadrant:

A back observation quadrant was designed to take measurements of the sun’s altitude.

Uses of Quadrants

•   The quadrant, which was first used in the fifteenth century, was the most widely used navigational tool in the mid-eighteenth century.
•   A sailor would use this equipment to measure the angle of the sunlight over the horizon at midday to establish his ship’s position at sea. He would then use that measurement to compute his vessel’s height; celestial objects might be used to perform similar computations.
•   For aiming their cannons and measuring distance, artillery officers utilised a reduced quadrant called a gunner’s quadrant.
•   Astrologers used the quadrant to predict a solar eclipse or someone’s fate with the help of the stars. It was merely an instrument for determining the angular altitude of a star, including the sun.
•   Surveyors could use it to determine the height of a building or even a mountain. It was even utilised to assist in the firing of a cannon towards an enemy fortification.

Conclusion

A quadrant is a graduated arc that includes a quarter of a circle and is used in mathematics or astronomy. A shade of a horizontal peg cast on a 90-degree graded arc, situated on the meridian plane, was used to estimate the sun’s altitude at noon. The elevations of astronomical objects are measured using a mural quadrant. A geometric quadrant is a tool used by navigators and surveyors. The Davis quadrant is a framed, compact quadrant that estimates the elevation of an astronomical object and was also employed by navigators. Large, framed quadrants can be used to measure the angular distance of celestial objects. The dip angle of the elevation of a cannon or mortar’s gun barrel is measured with Gunner’s quadrant.