Heavens above

As we go about swiping our smartphones each day, we may feel as if we are participating in a uniquely modern experience. With the quick flick of our fingers, we can learn what time it is, what the weather may hold for the week, and how to navigate to our next destination. Never before has so much information been so readily available at our fingertips. Right?

In a certain way, that’s true. But centuries before the dawn of smartphones, humans were swiping through a different type of handheld device to gather some of the same types of information that we seek from our phones today. These earlier humans were not staring at LED screens but at astrolabes, analogue devices composed of layered discs and other swivelling features that offered information based on the position of stars in the sky.

Loosely translating as ‘star-taker’ in Greek, the astrolabe first appeared in the Roman Empire sometime around the 2nd century AD, and spread to the Islamic world by the 8th century. They remained in use up until the 17th and 18th centuries, when newer technologies like modern clocks and sextants became more reliable and made astrolabes obsolete.

In their heyday, these circular instruments met a whole suite of needs ranging from scientific to religious to mundane day-to-day decision-making. Some Europeans relied on them when strategising around things such as personal finances and military tactics, based on the position of stars in the zodiac. Astrology held more sway during parts of the Middle Ages than it does today. In the Islamic world, the device helped determine the time and direction of daily prayer called for within the Quran.

To use an astrolabe, you might first begin by looking through a pinhole on the back of the instrument to find a familiar star in the night sky. From there, you could determine the star’s altitude and carry on with additional calculations on the front of the device, where a round plate with a two-dimensional projection of Earth’s latitudinal lines sat layered with other rotating features. Because the position of stars shifts depending on the geographic location from which you view them, astrolabes often came with a collection of several different plates, each representative of the latitude of a different major city.

Sometimes constructed of wood, sometimes of metal, these versatile instruments ranged in size from as small as a coaster to as large as a bicycle wheel, depending on their intended use. Some were ornate and decorative – a sign of wealth or status not unlike a Rolex today – but others were plain and utilitarian. “For every fancy one, there were probably many more that were functional,” says Alexander Jones, a researcher at New York University who specialises in ancient astronomy.

More often than not, the higher-quality astrolabes are the ones that survive to the present day, since poorer quality devices have long since been recycled or decayed, says Jones. Many mariners’ astrolabes that have made it into modern collections were gathered from Spanish and Portuguese shipwrecks off the western coast of Ireland. Beyond these physical remnants, we also find traces of these instruments in works of fine art, including Vermeer’s The Astronomer (c.1668) and Paolo Veronese’s Allegory of Navigation with an Astrolabe: Ptolemy (1557), which depicts the famous Greek astronomer grasping a frisbee-sized astrolabe with both hands.

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The Regiomontanus/Bessarion Astrolabe (1462), which is to be offered in Bonhams’ Instruments of Science and Technology sale, has a rich history. Built in Rome under the patronage of Cardinal Bessarion (1403- 72), it passed through the hands of other esteemed European figures in the following centuries, including renowned Scottish mathematician and astronomer Mary Somerville (1780-1872), who worked as a scientist and science writer more than a century before such positions were readily available to women. Her two-volume textbook Physical Geography (1848), the first of its kind to be published in English, was widely referenced for at least half a century after she wrote it.

Somerville and her husband William gave the astrolabe to their friend John Herschel (1792-1871), polymath and dedicatee of Physical Geography. The device passed from Herschel to a few others before arriving at the National Maritime Museum in Greenwich in 1958, where it remained until the 1980s.

Though the use of these intricate instruments has been superseded in the 21st century, their beauty and intrigue live on. They still offer valuable information about our time and place in the universe, reminding us that what we consider purely modern is often just something reimagined from the past.

Laura Poppick writes on science and the environment. Her book Strata will be published by W.W. Norton.