Definitions

# Astrolabe definition/origin/Purpose/How it works

Developed by the Greek mathematician Hipparchus in Ancient Greece, the astrolabe is an instrument used to calculate the position of the stars from geometric principles. Astrolabe definition

In addition to the position of the stars, the astrolabe was used to calculate the altitude of objects, the depth of wells and also to specify the time and geographic locations.

From the 15th century the astrolabe became an important navigational instrument . With it, it was possible to determine the latitude of vessels and the directions in which they should sail.

The word astrolabe derives from the Greek words “ astron ” which means star and “ lamanein ” which means to catch.

## The origin of the astrolabe

The first astrolabe was created by the Greek mathematician, astronomer and geographer Hipparchus of Nicaea (180 – 120 BC) during the Hellenistic period of Ancient Greece. Astrolabe definition

An important student of mathematics, Hipparchus was one of the creators of trigonometry and was the one who discovered the precession of the equinoxes and the possibility of dividing a circle into 360°.

Based on several mathematical theories, Hipparchus developed this complex instrument that could perform calculations similar to an analog computer.

The creation of the astrolabe was made possible by the description of stereographic projection by Hipparchus. This projection is a method that allows the transcription of 3 coordinates to a two-dimensional plane.

From the 8th century, the astrolabe began to be used in the Islamic world and was discovered from the translation of materials written by the Greeks.

The Arabs used the astrolabe for navigation and also to determine prayer times and the location of Mecca, which direction they should face when praying. Astrolabe definition

The Arabs took the astrolabe to Europe, where the instrument was simplified and improved with the aim of guiding vessels that set out in search of new lands.

This new astrolabe became known as the nautical astrolabe and was developed by astronomer Abraão Zacuto in Portugal.

Unlike the ancient astrolabes, which performed various calculations, this new instrument had the sole purpose of determining geographic locations.

## What is the astrolabe for?

The astrolabe uses the positioning of the stars in the sky and principles of applied trigonometry to make various calculations. Among the functions of an astrolabe are: Astrolabe definition

• Precise the positioning of the planets and stars;
• Measure the height of mountains, buildings or the depth of wells;
• Determine the hours of the day and the seasons of the year;
• Determine the geographic positioning of vessels.

### Importance of the astrolabe to the history of navigation

The maritime expansion begins in the 15th century with the Iberians. At that time, the only points of reference for navigators were the stars, which were used as guide stars.

The Sun, the Polar Star and the Southern Cross, for example, used to be important points for determining geographic locations on the high seas.

As navigation develops, mathematical and astronomical instruments and techniques are created to locate vessels, define routes and discover new lands.

The astrolabe, which was taken to Europe by the Arabs, became an important tool for ships, as it allowed the calculation of locations from the stars and planets. Astrolabe definition

In addition to astrolabes, navigators used compasses, balestillas, compasses, declination tables of the sun and studied mathematics and astronomy.

## How does the astrolabe work?

The astrolabe is made on a circular metal plate on which several circular blades with different graduations are superimposed, such as hours of the day, degrees, months of the year and zodiac signs.

The nautical astrolabe is very similar to the first astrolabes, but its structure is simpler and usually has indentations inside the metal plate.

In the middle of its structure is a pointer linked to the circular plates and at the top a handle so that the astrolabe can be held in a suspended way. Astrolabe definition

To use the astrolabe, the observer points the central ruler to the star used as a reference and then observes the instrument’s graduations.

From this observation and based on astronomy knowledge, navigators could pinpoint their location on the high seas and calculate routes.