steampunk-and-junk: Functional, Semi-Profess…


Functional, Semi-Professional Brass Nautical & Aviation Sextant

A sextant is a very important mathematical instrument for navigating at sea. It can also be used in astronomy. It is used to measure the angle between two far away objects. Most often these objects are the sun and the horizon, or the pole star and the horizon. Sometimes the angle between the horizon and stars or the moon can also be measured with a sextant.

The original Ross London sextants (on which this replica unit is authentically based) were made in England at the end of the 18th century. The biggest problem for sailors in the 18th century was finding their position in the middle of the oceans during long journeys. Sailors needed to be able to find both their latitude (which was their position north or south on the earth) and their longitude (which was their position east or west on the earth). Sextants helped them to find out both of these things. Before the invention of satellites and electronic satellite navigation systems it was very hard for sailors to find their position at sea. Many shipwrecks occurred because captains got the positions of their ships wrong. This not only caused the deaths of many seamen but also had big political and economic implications for the government because lots of battles happened at sea or valuable cargo could be lost in shipwrecks.

Sextants are made with a circular curve that is one sixth of a circle. The curve is divided up like a protractor. It is used for measuring angles so it is labelled with degrees. The other important parts of a sextant are a telescope, a piece of glass which is half see-through and half mirror (called the horizon glass), and a moving arm which has another mirror fixed to it.

 In earlier times, marine sextants had a fixed telescope leveled on the horizon and a radial arm is moved against an arc scaled in degrees. The radial arm is adjusted to get the reflection, of a known star, from index mirror and then off the horizon mirror down the telescope until it lines up with the horizon. The position of the radial arm on the scale gives the stars elevation. The nautical sextant range includes: slow motion nautical sextant, octants, slow motion nautical sextants and round dubble telescope nautical.

In modern navigation sextants, the light ray from the celestial body is reflected in two mirrors (in series) one of which is adjustable and the other is half silvered. By rotating one mirror and its attached index bar, the image of the body is brought down to the horizon. The rotation measures the altitude on the limb.