A 1000-year-old star catcher

This astrolabe was made by Muhammad ibn al-Ṣaffār in Córdoba in Al-Andalus (now Spain) during the period of Umayyad rule. It dates to the year 417 in the Islamic lunar calendar, which equates to 22 February 1026 to 10 February 1027 CE.

This means that in 2026 we are celebrating its 1000th anniversary. 

Date information can be found in an inscription in 'Kufic', a form of Arabic script, on the back of the instrument. This makes the astrolabe one of the earliest dated European-made astrolabes.

The inscription reads “Work of Muhammad bin [ibn] al-Ṣaffār in Córdoba in the year 17 and 400”.

What are astrolabes?

The origin of the astrolabe was probably ancient Greek, but the instrument as we know it dates to around the 8th century.

Astrolabes are a model representing the motions of the Sun and stars, as seen from the perspective of Earth. They are used to observe, calculate and predict the position of Sun and stars. Common purposes include time-keeping, wayfinding and astrology.  

The word ‘astrolabe’ comes from the Greek 'astrolabes' (star-holder/taker). The 'rete' (net or web in Latin) is the rotatable front part of the device which points to stellar positions on the plate below and shows the ecliptic (annual path the Sun appears to take through the sky). The main body of the astrolabe is called the 'mater' (mother in Latin). This can hold several plates, engraved with stereographic projections of the celestial sphere as seen from different latitudes.

Astrolabes are 2D versions of the 3D model of the celestial sphere, known as an armillary sphere. They also have some similarity to planispheres, which are circular star charts. However, the changeable plates mean the astrolabe can be used at several different latitudes, and the additional lines and scales provide many more functions.

Astrolabes are used to observe the position of the stars to help calculate the time, date or position of the observer. For example, as well as establishing the correct time for daily prayer, the astrolabe could be used to work out the direction of Mecca. They can also be used to calculate the timing of celestial events, in the present, past or future, and to measure heights and angles on Earth.

To get a better idea of how an astrolabe works, you can play with this simulation, created by data scientist Alex Boxer. In this YouTube video, historian of science Taha Aslan shows how to calculate the time.

Anatomy of an astrolabe

There are two other surviving astrolabes signed by the same maker, Muhammad ibn al-Ṣaffār. One is dated 411 AH / 1020 CE and is now at the Islamic Arts Museum in Malaysia. The other is dated to 420 AH / 1029 CE and is at the Staatsbibliothek zu Berlin.

The 420 AH astrolabe, made in Toledo, includes added Hebrew script. This underlines the cultural and scientific interchange that took place in medieval Spain. The instrument is also the only one of the three to have its original rete.

The rete on our instrument was made later, likely in the 13th century.

The rete is used in conjunction with changeable plates kept inside the body of the instrument. In the case of our 417 AH astrolabe, there are seven plates, engraved on both sides to be used at 14 different latitudes. These latitudes include locations such as Mecca, Medina, Córdoba, Tangier and Constantinople.

The engraving on the plates includes:

• latitudes and place names
• stereographic projections of the celestial sphere
• lines indicating times for the five daily prayers

The back of the astrolabe is engraved with a shadow square, used to measure heights and calendrical scales, as well as the sighting vane, or 'alidade'.

The Ibn al-Ṣaffār brothers

The maker’s brother, also known as Ibn al-Ṣaffār, was a teacher of astronomy and geometry in Córdoba. He wrote a treatise on the use of the astrolabe, which was translated into Latin, Hebrew and Old Spanish. It was in use in Europe until the 15th century. 

The brothers’ name is literally, and aptly, translated as 'son of a copper smith'. Brass is an alloy of copper and zinc, and in this case, the main body of the astrolabe has been calculated as around 80% copper and 20% zinc. This is a higher proportion of copper than became common in later brass objects.

A second-hand shop find

Before National Museums Scotland acquired it, this astrolabe belonged to James H. Farr, who ran Wardie Garage on Ferry Road. In 1959, Farr attended a lecture on astrolabes by Robert Plenderleith, Keeper of the Royal Scottish Museum’s Technological Department. This prompted him to have his astrolabe dated. On learning quite how old his astrolabe was, Farr decided to give it to the National Collection. He told The Scotsman that he “bought the astrolabe about ten years ago in a second-hand shop in Edinburgh’s Lawnmarket”.

The astrolabe was originally displayed with horological collections at the Museum. Today, it sits in the Earth in Space gallery, which shows how stars and planets have been observed and used for timekeeping and navigation.

In 2024-25 it was loaned to the British Museum’s Silk Roads exhibition. There, it was displayed with other artefacts from Córdoba during the period of Umayyad rule, showing its cosmopolitan nature and cultural flourishing. 

Table of places and latitudes on the plates

The seven plates serve the following latitudes.

These places are paired on the plates:

• Sanaa and Mecca
• Medina and Samarra
• Kairouan and Córdoba
• Zaragoza and Equator
• Sheba and Cairo
• Clysma and Tangier
• Toledo and Constantinople.

The Ecliptic plate is engraved inside the mater.

Table of stars carried by the rete

The pointers on the 13th-century rete have been calculated as pointing to 21 bright stars:

• 11 in the northern celestial hemisphere
• 12 in the southern celestial hemisphere

Here they are listed by position on the rete, east to west.

The astrolabe is on display in the Earth in Space Gallery on Level 1 at the National Museum of Scotland.