Question

The instrument used to determine the angular distance between two objects is called_________.
A. Periscope
B. Sextant
C. Hydrometer
D. Telemeter

Answer 1

Hint: The principle of this instrument was firstly implemented around the year 1731 by John Hadley and Thomas Godfrey but it was also found afterward in the unpublished writings of Isaac Newton.

Complete answer: A sextant refers to a doubly reflecting navigation instrument that is used for measuring the angular distance among the two visible objects. The main use of a sextant is to measure the angle between an astronomical object and the horizon basically for the purposes of celestial navigation.
The estimation of this angle, the altitude, is typically known as fighting or shooting the object, or taking a sight. The angle, as well as the time when it was measured, can be utilized for calculating a position line on a nautical or aeronautical chart.
A sextant is also used for measuring the lunar distance between the moon and another celestial object (like a star or planet) for determining Greenwich Mean Time and hence longitude.

Thus, Option B is the right answer.

Note: The name of this instrument is derived from the Latin Sextus, or “one-sixth,” for the sextant’s arc spans 60 degrees or one-sixth of a circle. Octants, having 45 degrees arcs, were first used for calculating latitude. Sextants were firstly developed with wider arcs in order to calculate longitude from lunar observations, and they replaced octants by the second half of the 18th century.