How did an Italian astrolabe end up on the New Zealand passport?

A few years ago I enjoyed a blog post in which National Maritime Museum curator Rebekah Higgitt wrote about the "navigation" theme of the new New Zealand passport design.  Higgitt discussed the use of John Harrison's H1 clock as an illustration in the passport.  She also noted that the description on the New Zealand government website mentioned an astrolabe, which piqued my interest.  I tried to find out more, but the website didn't include pictures, and none of my Kiwi friends had new-style passports.

So I forgot about it... - until last week when a friend of mine was talking about the designs that have been proposed to replace the current NZ flag.  I took the opportunity to ask to see his passport, and bingo! Here it is:

I was intrigued by the distinctive design and decided to see if I could find similar astrolabes in any published museum collections.  It didn't take me very long to track down this one:

Image courtesy of Museum of the History of Science, University of Oxford

This is astrolabe 50257 at the Museum of the History of Science in Oxford.  You don't have to be an expert to spot the similarities.  But the question is, are those similarities remarkable? How unusual is this design?

To answer that question, let's go back to basics for a moment.  The similarity you notice - the dark pattern of rings, heart shape and so on - is the rete of the astrolabe.  It was made by cutting holes in a sheet of brass, so that it resembles a net (that's what rete means in Latin) or, as Chaucer thought, a spider's web.  It sits inside the mater of the astrolabe, and rotates around that big pin in the middle.  Each of the pointers on the rete marks a star, making the rete a moving star map, able to simulate the daily (apparent) motion of the heavens around the earth.

This overall layout, with the rete turning above a plate engraved with a grid of coordinates and a horizon for a particular latitude, is by far the most common form of an astrolabe.  The basic concept goes back to Ptolemy in the 2nd century CE, and the instrument had this settled form, with the mater, interchangeable plates for various latitudes, the rete and rule (which also moves, as you can see from its differing position in the two pictures above), by the time John Philoponus wrote a description of it in the early 6th century.

But that still left a lot of flexibility for individual designers and craftsmen.  They could choose which stars to include on their rete, but more noticeably, the supporting brass "net" could be almost any shape, as long as it included that smallish eccentric (off-centre) circle which is the ecliptic, mapping the Sun's annual progress through the zodiac.  Craftsmen expressed their flair through ingenious designs - a favourite trick, as you can see here, was to make the rete symmetrical, even though the stars obviously weren't.

As far as I know, this particular design of rete is unique.  Luckily the astrolabe itself has the name of its designer on the back: Giovanni Domenico Fecioli of Trento, in the far north of Italy.  We also have the name of the man who commissioned it: Giulio Cesare Luchino, of Bologna.  The latitude of Bologna is 44° 30', which matches the astrolabe's single latitude plate.  It's dated 1558, just when the popularity of astrolabes in Europe was at its peak.

Image courtesy Museum of the History of Science, Oxford

In technical terms there's nothing particularly remarkable about this astrolabe, but the design is an attractive one.  The illusion of interlocking circles at the bottom of the rete was a popular motif in that period - compare, for example, this one by the prolific Arsenius workshop in Louvain.  Arsenius was famous for his tulip-shaped designs (can you see the tulip?), and Fecioli's rete doesn't quite match the delicacy of Arsenius's intricate brasswork, but it's still beautiful, and I'm sure it was much prized (and proudly displayed) by Luchino.

I have no idea why the New Zealand government chose a Fecioli astrolabe as an illustration for their passports.  But it's worth saying a few words about the place of this instrument in the overall design scheme.

Here's what their website says about it:

The passport’s new design evolved from the concept of navigation and our evolution from a place of discovery, to a place of destination and follows the journeys of the earliest explorers of New Zealand through to the journeys made by Kiwis today. Themes of arrival and departure, navigation and time are represented figuratively and metaphorically throughout the passport.

And about pages 20-21 specifically:

The astrolabe and chart – the astrolabe is an astronomical instrument used by astronomers, navigators, and astrologers. Its many uses included: locating and predicting the positions of the sun, moon, planets and stars; determining local time using local longitude and vice-versa; surveying and triangulation. 

Of course the theme of navigation is perfect for a passport.  But the astrolabe's place in that theme is less certain.  It was a multifunctional compendium of astronomical and astrological functions, not particularly suited to use at sea.  It's true that the mariner's astrolabe was a popular navigational device (I made and tested one for a previous blog post), but that was a quite different instrument.  It's certainly highly unlikely that Fecioli's beautiful piece ever went offshore.

Even if it had, it could never have been used to determine longitude (or to predict the positions of the Moon or planets).  The relationship between longitude and time was well known in the age of the astrolabe, and astrolabes could certainly be used to find local time.  But longitude is a relative measurement (these days we measure it east or west of Greenwich); if you want to go from local time to local longitude, you also need to know the time at the reference point (e.g. Greenwich) from which you're measuring longitude.  Local time was easy to find, but when Fecioli made his astrolabe, a reliable, robust method of keeping reference time - a clock that could withstand ocean passages - was still 200 years away.

But local time itself is unattainable with the astrolabe pictured in the passport, because the designers have cut off the suspension ring and throne that attaches it to the mater.  The ring is crucial for sightings of the Sun or a star, because the astrolabe has to hang vertically.  Without it, the astrolabe is no longer an observational instrument.

That may seem like nitpicking, but it tells us something about the way astrolabes are (and were) seen.  They have always had symbolic value, representing astronomical knowledge as well as artistry and the owner's wealth and status.  Today in many museums they are presented as art objects, out of context and, often, supported from below rather then suspended by the ring (admittedly for sound preservation purposes).  They now seem to symbolise ancient, arcane knowledge, and this symbolic value trumps accuracy, much like the "save" icon in most computer programs is a 3.5" floppy disk, though you're unlikely to be storing your work on those any more.

Of course I don't mind that - I'm happy people find astrolabes evocative and attractive.  And, as I say, they've always had symbolic value.  But once in a while it's worth reminding ourselves of the specific contexts where, for a thousand years, they were also complex scientific objects with practical purposes.

Update, 25/08/2015: I wrote to the New Zealand Passport Office to see if I could find out more, and received a very friendly response.  The officer wrote: "I have spoken directly with some of those involved in the design process of the latest version of the New Zealand passport, which was produced in 2009 and the astrolabe design appears because it is a symbol for travel and a relatively complex shape. [...]
The specific astrolabe was not chosen for any particular reason except that it fit with the overall theme.  I was unable to ascertain whether the astrolabe featured in the book is the specific 16th century Italian you have identified but your analysis would suggest that it is the case.  Unfortunately I am not able to be more specific than that.  
Thank you very much for writing to us and I have noted with pleasure your compliment for our 'beautiful' passport."

Historic navigational instruments on trial

I started this blog when I reconstructed a medieval equatorium.  I wanted to understand how it worked, and the best way was to follow the instructions in the unique manuscript that describes it.

Last weekend I did it again, with three different instruments: a sextant, a cross-staff, and a mariner's astrolabe.

I only made two of these myself.

I'm a keen sailor, and one reason I first got interested in history of science was because of my fascination with navigational techniques.  Lots of stories are told about great explorers, but we rarely hear about their tools and techniques.  Sometimes we hear about great inventions, but those stories are often misleading.  So while everyone knows about John Harrison and his amazingly reliable clocks that helped solve the problem of finding longitude at sea (I recently reviewed the National Maritime Museum's wonderful exhibition on this subject), people don't always appreciate that knowing Greenwich time was only helpful if you could measure your local time accurately.  This was done by observing the altitude of the Sun.  And that was the purpose of all three of the instruments above.

Actually that's not quite right.  The mariner's astrolabe, which came into common use in the late 15th century, started out as an instrument for stellar, rather than solar observation.  It was well known that the altitude (angle above the horizon) of the Pole Star was almost equal to the latitude of the place of observation.  It was also known that the Sun's zenith distance (90° minus the altitude) at noon on the equinox was equal to the observer's latitude, but declination tables to simplify the calculations necessary on other days of the year were not drawn up until the very end of the 15th century.  That's why the first mariner's astrolabes measured altitude, while on later ones the scales were reversed to measure zenith distance.

Mariner's astrolabe in use. From Pedro de Medina's
Arte de navegar (1554)

The earliest mariner's astrolabes were made of wood - we know that Vasco da Gama had a large one, about 60 cm in diameter, on his first voyage to India in 1497.  Columbus also used an astrolabe (as well as a quadrant), though we can't be sure what it was made of.  The oldest surviving terrestrial globe, the Erdapfel of Martin Behaim, contains an inscription urging navigators to use an astrolabe.  These were soon made out of brass, which was a more durable material than wood.

From John Sellers'
Practical Navigation (1672)

The cross-staff (or Jacob's staff) incorporated simple trigonometry to measure the angle between two objects (such as the horizon and the Sun).  Although it was probably invented in the 14th century, it was not used for navigation until the 16th century.  Before then, most sea travel took place along known routes, staying within sight of land whenever possible - precise measurement of latitude was pointless.  It was only with the first trans-oceanic voyages at the end of the 15th century that the cross-staff and mariner's astrolabe became essential navigational devices.

The purpose of this blog post isn't to give the history of these instruments.  There are lots of great websites and books that do that.  I just want to write about what I learned at the weekend.

I made the cross-staff using the instructions at Richard Paselk's very informative site.  The mariner's astrolabe was just a copy of ones I've seen in books and museums.  They were both made out of off-cuts of wood I had lying around, which I sawed, glued and screwed into shape with the basic tools I have at home.  I finished them just in time for the trip I was skippering for Cambridge University Yacht Club.

I planned the trip for the new moon, hoping that we'd see some good stars (the partial solar eclipse on Friday morning was a bonus).  So, fuelled by chicken and chorizo pasta and some chocolate brownies, we set off from Ipswich on Friday evening at about 10.30 pm.  Sadly the cloud blocked our view of the stars that night.  The following day high winds and rough seas (not to mention more cloud) meant that we were more concerned with sailing the boat safely and effectively, than with astro-navigation.  But on Sunday afternoon the cloud finally cleared and we were able to try out the instruments.

Navigating Puffin up the Orwell

I took some sightings, compared them with my modern plastic sextant, and was pleased to see that both instruments were accurate to a degree or better.  I'd made two cross-pieces of different lengths for the cross-staff, and had done the trigonometry in advance, marking the angles directly on the staff (the further you push the cross-piece away, the smaller the angle between its two ends).  The result was a surprisingly versatile instrument: as well as measuring altitudes, it could also be used to measure the horizontal angle between two (or more) landmarks.  So if you have those landmarks on a chart, you can use the cross-staff to fix your position relative to them.  It was easy to make and pretty robust.  On the downside, it requires the user to point it directly at the Sun, which is pretty hard on your eyes!  It's not surprising that it was superseded by the back-staff, which could be pointed away from the Sun.

I was less impressed by the mariner's astrolabe.  It was more difficult to make: dividing a circle accurately was a major challenge.  For angles between 10 and 80 degrees it was harder to read than the cross-staff. And despite the fact that I'd made it with holes in the disc, it swung a little in the wind.  I probably should have made it out of brass instead of MDF, I suppose.  On the other hand, you can use it to measure the Sun's altitude without blinding yourself, by letting the shadow of the top sight fall on the bottom one.  But sadly the damp conditions on the boat softened the glue and one of the sights fell off... I bet that never happened to Columbus.

It was fascinating to compare these instruments with my modern sextant: the model I have can measure altitudes to 2' (1/300th of a degree).  My productions weren't that good, but I was pleased that they gave moderately accurate results even though I'm hardly a master craftsman.  Knowing your latitude to within 60 miles isn't much use if you're trying to thread your way through Suffolk sandbanks, but it might help with oceanic passages.  Above all though, I was impressed by the early-modern navigators, whose lives depended on their ability to take accurate sightings, no matter how rough the sea or how fleeting a glimpse of a star they could get.  It makes me appreciate our GPS all the more.

Ships, Clocks & Stars

I recently visited, and very much enjoyed, the exhibition at the National Maritime Museum about the quest for longitude.  It's on until 4th January, and I highly recommend it.  I liked it so much I wrote a review of it for the Science Museum journal!