Sextant

A sextant is an instrument with the help of which one can measure a celestial object’s altitude above the horizon. Several terminologies are given to making this measurement by experts, such as taking a sight, shooting the object, or sighting the object. A sextant is used to measure an object’s angle. Moreover, one can also calculate the exact time of the measurement by using sextants. 

With the help of this knowledge, calculations of a position line on a chart become possible. This chart is known as an aeronautical chart or simply a nautical chart. Now, let’s take a look at the different types and uses of sextants.

Types of Sextants

There are three types of sextants, and they are as follows:

• Nautical Sextants

• Box Sextants

• Sounding Sextants

Nautical Sextant

A nautical sextant is an instrument that is primarily meant for determining the latitude and longitude. This sextant is used to measure angles between two objects of celestial nature. Celestial objects can be:

1. Sun

2. Moon

3. Stars

4. Comet

5. Any other celestial body

The sighting of these celestial objects takes place by using a nautical sextant. It is used to determine the following:

• Angular measurements between celestial bodies

• The horizon

Nautical sextants are also known as:

• Vernier sextants

• Marine sextants

Box Sextant

This can be described as a small pocket sextant. It appears as if it is enclosed in a box. Due to its small size, its diameter is just 75 mm.

Just like vernier sextants, box sextants are also useful in calculating horizontal and vertical angles. Due to its petite size, a box sextant has the advantage of being portable. It is also fit to be utilised in ships for celestial navigation. Moreover, box sextants are reliable in carrying out measurements on a ship in motion.

Sounding Sextant

This is similar to the nautical instrument. The only thing that separates these sextants is a relatively larger index glass of a sounding sextant. It is used in calculating the sea or river depths.

Sounding is located by a variety of methods. A commonly used method is to locate it by calculating angles from either one of the two:

• Shore

• Boat

Uses of Sextant

Now let’s discuss the uses of sextant pertaining to its different types.

Uses of Nautical Sextants

• Nautical sextants are used for navigational needs on ships and boats.

• Experts use them for astronomical needs to carry out angular calculations between celestial bodies.

• The calculation of the angles may take place in any plane with the help of nautical sextants. This calculation can be in the object plane or the telescope plane.

• The calculation of the vertical angles with nautical sextants can take place by reducing its horizontal angles.

Uses of Box Sextants

• Box sextants can be used as an optical square. For this, you will have to set the vernier to 90o.

• Box sextants are used to calculate the angles in chain surveying.

• Experts use them to check the angles that are calculated by other instruments for surveying.

• A box sextant is also used for radiation in traversing.

Uses of Sounding Sextants

• A sounding sextant serves the role of being a crucial marine instrument. It is used typically for the measurement of the angles between coastal features. This way, one can locate a boat or ship’s position relative to the shore.

• It is also helpful in locating sounds in hydrographic surveys. It provides more accurate and reliable values than the typical nautical sextants.

Important Pointers to Keep in Mind While Using Sextants

While using sextants, it would be wise to remember the following important pointers:

• Before using them, always make sure to check the errors.

• Look at the horizon while focusing on the telescope. As you do this, create a mark on the stem’s circumference.

• Make sure that the instrument is held in a steady position while using it. To accomplish it, stand such that your feet are slightly apart. This way, a suitable balance with hands will be achieved. This would lead to a firm and steady holding.

• Swing the instrument to the other side while observing the celestial body’s altitude. This way, the body will seem like projecting a movement along the arc. Now, the measurement of the altitude at the lowest point can be carried out effectively on this arc.

• Stand as close as possible to the ship’s middle line or the centre line.

• Use appropriate dark shades while observing the Sun.

• Keep in mind to rotate the micrometre whenever there is a detection of a backlash error. This rotation must take place in one direction only.

• Calculation of the altitudes of the celestial body must be done during the time of twilight.

• Avoid making observations at night-time as far as possible. This is due to the fact that strong moonlight creates an illusion of a good horizon, which, in most cases, is not true.

Conclusion

A sextant is an instrument with the help of which one can measure a celestial object’s altitude above the horizon. Making measurements using sextants is termed by experts as taking a sight, shooting the object, or sighting the object. There are three types of sextants – nautical, box, and sounding sextant. The uses of sextant of these three types also differ from one another.