Cassini – Science the Church and a Gnomon

As the Cassini Saturn probe prepares for its final few orbits before being de-orbited into the planet, it’s worth considering who it was named for – the C16th Italian astronomer Giovanni Cassini. These days the Vatican collaborates with the European Space Agency and NASA on space science. Even the Vatican Library uses an image file storage system developed by NASA – it was a system originally designed for radio astronomy.


But it is worth remembering that the Church has often had an uneasy relationship with science. Galileo Galilei was tried in 1633 for heresy by the Inquisition and was sentenced to formal imprisonment – one of the Church’s ‘oops’ moments – later commuted to house arrest.

In 1582, when Galileo was just 18, Pope Gregory revised the calendar, as the Julian calendar developed under Julius Caeser was getting embarrassingly out of step with the solar year (it lacked leap years). But the introduction of the more accurate Gregorian calendar that we use today, presented a new problem. The major Feast Days needed some re-calibration. The most difficult one was Easter – a so-called Moveable Feast – and a pretty important one to the Christian faith. It was supposed to fall on the Sunday following the first full moon after Spring Equinox (20 March). While today we just look it up on Google or wait for Facebook to remind us, it was a bit more complicated back in the C16th. You see, the problem was that the Church followed the lunar year, while everyone else followed the solar year, and they don’t quite match up. It was time to find some astronomers who hadn’t yet been executed for heresy, and who would admit to being astronomers… no pressure then.

Genovese astronomer Egnazio Danti (cosmologist to Cosimo de Medici I) was called to Bologne to work with Pope Gregory’s Calendar Commission to help determine accurate dates for the Spring Equinox – and by extension, Easter. He constructed a Gnomon – a sight line – inside the Basilica of San Petronio in Bologne and cut a hole high in the wall to allow the sun to shine through onto the gnomon. This was used to determine the path of the sun at certain times of the year, and help with measuring the lunar cycle too. But less than 100 years later, some renovations designed to expand the Basilica meant that the wall with the hole for the sun was removed (oops)… So in 1655, a mere 20 years after Galileo’s death, Giovanni Cassini was brought in to design a new gnomon in the same church. His ambitious plan was to build a much longer gnomon for more accurate observations. His ulterior motive was to prove Galileo’s observation that the Earth went around the sun, not the sun around the earth – this time without getting into trouble with the Inquisition.

So what has this to do with travel? You can still see Cassini’s gnomon today in the Basilica of San Petronio in Bologne. But if you are visiting Rome you can find another Gnomon – it’s worth checking out the floors in some of these churches, and look for an angled line in bronze running across the floor… There’s also one at the Church of San Sulpice in Paris (pictured below) – made famous by the movie of Dan Brown’s ‘The Da Vinci Code’.

Church of St Sulpice Paris

The C16th Basilica of Santa Maria Degli Angeli in Rome was dedicated as a Basilica in 1920 by Pope Benedict XV in 1920. But from the outside, it doesn’t look much like a church at all. Curiously, it was built inside the ruined Frigidarium of the Roman baths of Diocletian (ca 300AD), thus preserving a significant part of the ancient Roman building into the modern age.


Basilica of Santa Maria degli Angeli

The church itself was designed by none other than Michelangelo. So, from a simple ancient Roman exterior, you enter into a magnificent Renaissance church of breathtaking scale – one of the world’s largest.

Basilica of Santa Maria degli Angeli

But I had heard that it held one more surprise. A gnomon. The gnomon here was copied from Cassini’s design. Pope Clement XI commissioned the astronomer Francesco Bianchini to construct the Gnomon. Bianchini was Secretary of the Calendar Commission, and h chose the Basilica of Santa Maria degli Angeli because of the stability of its Roman walls and foundations, and because of its height and large internal space. Bianchini improved on Cassini’s design by allowing for the observation of stellar transits – even in daytime.

Basilica of Santa Maria degli Angeli

Here you can clearly see the sun approaching the meridian line.

The pinhole occulus through which the sun shines is located high on the wall, and to give it a clear path, part of the entablature and the capital of the pilaster – designed by Michelangelo – was cut away – perhaps a metaphor for the tension between art and science and the church! I have added an arrow to show where the sun enters.

Basilica of Santa Maria degli Angeli

The church also houses a Foucault pendulum which demonstrates the earth’s rotation through the pendulum’s elliptical swing.It was invented by French scientist Leon Foucault, who first demonstrated it in 1851 at the Paris Observatory – it now resides in the Museé des Arts et Metiers in Paris.

Basilica of Santa Maria degli Angeli

The pendulum weight is in the form of a globe as though pushed with a giant hand. Metaphors for force were quite literal! As you can see below

Basilica of Santa Maria degli Angeli

So, from a C16th astronomer seeking to solve the Church’s problem with Easter through detailed observations of the Sun, to a spacecraft providing detailed observations of Saturn we can glean nearly five centuries of the Church’s relationship to science and the arts by visiting a two-thousand year old Roman bath house renovated by Michelangelo in Rome. And all this, from noticing a strange geometric pattern on the floor of a church! It does pay to look down sometimes!

The value of noticing

Noticing – taking the time to observe things – when you travel, is a way of enriching your travel experience. I have often told people that a camera has taught me to see. By that, I mean, I have learnt to observe more, to notice the light and the play of shadows, and from that, I have learned to notice small details that others often overlook. This, in many ways, is the essence of mindful travel.

More recently, I have taken to using a sketchbook, though I can’t really draw for nuts. But the drawing is not the point. When I sketch, I spend time really looking at my subject, whether a building, or an unusual machine, or an interesting flower. When you sit in front of an object for an hour, trying to capture its form with a pencil, you end up noticing details that you never realised were there. It can help to make sense of how the object functions as it does, or did.

Studies have shown that visitors to art museums and galleries spend on average just a few seconds – rarely 30 seconds to a minute – in front of any given artwork. This is a process that Worts (2003) has described as grazing. We seem to be in a world of ‘swipe left’ as we travel to exotic locations to grab a quick selfie, before moving on.

crowd in the Louvre

On a recent visit to the Louvre in Paris, I was amazed at the crowds who surged into the room to grab a phone or tablet photo of the backs of the heads of everyone else who had come to see Leonardo’s Mona Lisa. What was remarkable, wasn’t the popularity of THAT painting, but the fact that they surged unseeing past FIVE other Leonardo paintings to get to be part of the crowd, such as the Virgin on the Rocks – which has a companion painting of this subject by Leonardo at the National Gallery of London.

Leonardo-Virgin on the rocks [Louvre]

But don’t get me wrong, I have nothing against people taking selfies, or against people taking reference photos for later viewing, perhaps as a reminder when they are trying to contextualise what was special about that particular artwork. But it is curious when the lens is used as a substitute for actually looking, and in that context I wonder what they are getting out of the experience, other than bragging rights with social proof that you have ‘been there’. But have you actually been there?

I ask that because I have been wondering lately about the link between being and observing. About 100 years after Leonardo painted the Mona Lisa, a Frenchman by the name of Renée Descartes came up with the idea that “I think therefore I am”.  And that seemed to settle the matter for a while. But around 1980, another Frenchman by the name of Jacques Lacan re-phrased it, suggesting “I think of what I am where I do not think to think.” In this case, he is suggesting that being and thinking are not necessarily the same thing. We can be in a place, but our mind is elsewhere. How often do we see a group of people having coffee together, each on their phone deep in textual conversation with someone not present at the table? To outsiders, it can seem disconcerting, but despite the mediation of the phone, at least they are being sociable with someone, even if not their present company.

Underground train London

A recent article in an e-journal called Aeon, titled “I attend, therefore I am” suggests that we are what we pay attention to. The article, by Carolyn Dicey Jennings, describes attention as “what you use to drown out distracting sights and sounds, to focus on whatever it is you need to focus on.” This power of attention, she argues: “…is what helps you in moments of conflict more generally – moments when you are caught between two (or more) options, both of which appeal to you, and you are torn on which option to choose.” Jennings goes on to observe that the philosopher Robert Kane describes these life-defining moments as ‘self-forming actions’. That is, actions that form and inform who you are as a person. The movie ‘Sliding Doors’ is a good example of how these life defining moments can turn on whether or not you catch that train, or take that trip.

A Canadian friend whom I met on the Camino, Kristine MacMillan has written a poignant blog post about this. In it, she talks about the value of following your dreams. She observes that you can’t predict when you’ll meet Mr Right, but you can control whether you learn a language, or take a trip

“…as a nurse I often see people who have saved or worked hard their entire lives with plans to start living when they retire, or to take that dream trip in 5 years time. Then they or their partner’s health fails and they don’t get that chance. ”

Some might describe this as a philosophy of Carpe Diem – Seize the day. Kristine puts it this way:

“it’s good to have dreams, but for me living a full life is essentially a way of living your dreams as best you can in the now. I don’t really have much control over when I meet Mr Right. But I can control whether I want to learn a second language, bicycle in the vineyards in France, or go on an African safari. I can choose these things by choosing not to pay for cable TV, or have a collection of purses, or put off buying a new iPhone. I tend to view things in terms of well that such and such thing is a plane ticket, and I’m way less inclined to spend my money on it.”

It all comes down to a question of focus. A camera and sketchbook have taught me to see, to focus on what is in front of me, to look around and notice my surroundings, and to observe the context – what makes it work, how did it get to be like this? how did it come to be there and not somewhere else? And by noticing, I am informing myself, and becoming who I will be, informed by what I have paid attention to in the past. We are, as the French philosopher Michel Foucault suggests, the sedimentation of our experiences that form the bedrock on which I base my future actions.

So how do I apply this? Last year, on the Camino de Santiago, I was taking a difficult path down towards the town of Portomarin. Mostly, I was focussed on trying not to twist my ankle on the uneven narrow path, but I also took moments to look around to see where I was and how far I had come. On one of these pauses I looked around and saw an opening in the rock like a small cave, and there was water running from it into a channel beside the path. I looked closer and took out my camera. It appeared to have been worked and shaped by human hands using hand tools, perhaps in ancient times. And I wondered if perhaps it might have been a spring used by the Romans to supply water to the town. I asked several people – fellow pilgrims – about it, and not one of them had noticed it was there. It might well have been a sacred water supply in pre-Christian times, or it might have supplied water to Roman industry nearby. Noticing that, and knowing that there were Roman copper mines nearby, enriched my experience of that place, and has made me want to learn more of the Roman and pre-Roman occupation of this area.


In another time, another place, others have sketched in the Roman forum in Rome, or  at the Colosseum, and in the process have observed how the place functioned, perhaps imagining the entertainments performed there, but coming away richer for having noticed how it was put together, and how the seats related to the Emperor’s box, and how the building was there in that place to help wipe out the memory of a tyrant. For others, it was perhaps a selfie moment, or a graze past from a tourist bus, but how much richer is the experience when you focus and notice and observe!



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Cruz de Ferro – a poignant moment

As the sun came up beneath an overcast sky, we set off from Rabanal del Camino en route to Cruz de Ferro.

Rabanal del Camino

The track mostly followed the road, and at one point we heard an extraordinary noise, like the breathing of a mechanical dragon or perhaps an ancient Bolton and Watt steam engine. What appeared was a strange white mad-max-style vehicle driven by two blokes in hi-vis vests as the machine drove down the centre of the road applying bursts of paint to form the dashed white centre line. Then for several hundred metres, we could smell only the paint.

Line painter

Behind came a slow van that stopped periodically to see how quickly the paint was drying. I tried to imagine the life of a Spanish council worker whose sole job was to just to watch paint drying. I hoped he was a budding philosopher, or perhaps a popular singer by night.

The rocks on the path interrupted my reverie and I was reminded of the one in my pocket, and thought solemnly about the Cruz de Ferro and what it meant for me.

There was a wooden cross at the entrance to Foncebadon – on it was a sign in four languages asking people not to place rocks on it. Perhaps some people have been mistaking it for the Cruz de Ferro.


At Foncebadon we stopped for eggs on toast and coffee – protein to sustain us for a long day.

The town was largely derelict aside from a couple of Albergues – one claiming to be a Druid Albergue. But its fortunes have been linked to the Camino since at least the C12th. It had its own pilgrim hospital, hospice and church built by the hermit Gaucelmo. The ruins of these are still visible as you leave the village. After shrinking to its last two inhabitants, Foncebadon is experiencing something of a revival thanks entirely to the resurgence of the Camino in recent years.


We walked on. At one point someone had strung a rope across the path with many smaller ropes dangling down like a giant fly curtain. I wryly thought they were trying to keep the flies from reaching the high country – it was more likely to discourage wayward cows.

Path to Cruz de Ferro

At length, the Cruz de Ferro came into view. We were beaten by a large contingent of Italian cyclists, who spent their time noisily trying to take selfies or posing for group ‘victory’ shots. They carried on despite others trying to have a solemn moment.

The tradition of the rock dates back in history, and there are differing versions of how the ritual began. Essentially the idea is that you bring a rock from home, to symbolise the burden of your sins or your psychological burden. You would carry it on the Camino as a reminder of your purpose, and it would be your Camino burden. You would then place your rock or significant object at the foot of the cross to symbolise unburdening yourself from your past transgressions.

Cruz de Ferro

I took my chance during a lull, and said a short silent prayer (not the one scripted for the Martin Sheen movie). Placing the rock (my Camino burden) at Cruz de Ferro was a poignant and personal moment, and just as I had placed the rock, I had a tap on my shoulder and turned to find a grinning Italian cyclist wanting me to take his photo. With a Zen-like realisation, I knew that that too was a Camino lesson.

Cruz de Ferro

I resisted the urge to crush their phone beneath a large rock, then shrugged. It’s their Camino too, whatever meaning this place has for them. So I smiled and took their photo and wished them a ‘Buen Camino’ – and meant it.

The Camino is different for everyone and in a way I was grateful to be distracted from my burden – after all, hadn’t I just let it go at the foot of the cross?

It was a strange and slightly surreal moment, but I did feel lighter for it, and so for me, it was a timely reminder not to dwell on the past when there are people in the present who need me – if only to take their souvenir ‘selfie’.

The cross is said to have been erected on the site of a Roman altar to the god Mercury, or perhaps a place of early Celtic worship – no-one really knows. The iron cross was erected in the 11th century by Gaucelmo, who was the abbot and founder of the monastery at Foncebadon. The current cross is a replica of the original now held in the pilgrim’s museum at Astorga. Some say the cross may originally have been erected to mark the path in Winter when the snow is deep. Whatever its origin, it is today a place of contemplation and a chance for pilgrims to pause and look within themselves and consider the purpose of their own Camino.

A chapel dedicated to St James was built in the Holy Year of 1982. A pilgrim sat in its shade to take a moment of reflection, perhaps waiting for the Italian peleton to resume their ride.

Chapel of St James

I also took a look around and found that a human sundial had been erected – it wasn’t in my guide – but I thought it a good way for people to consider their place in time and space by making them the gnomon or shadow pointer in a large sundial.

Cruz de Ferro sundial

There were instructions in English – although, with complete cloud cover and a heavy mist, it was difficult to get a proper shadow. The instructions stated:

  1. Place you in the central rectangle, put your heels on the centre line and move you more to the north or south depending on the month. The respective times for each 12 months of the year are recorded in the central rectangle. Your shadow will indicate in this way the true solar time (H.S.V.) Look Fig 1.

  2. To know the official time you should do the followin[sic] thing: add 1 hour in winter and 2 in summer. In addition, it is necessary to add the value of the equation M of the figure 2 (which is indicated in minutes).

We turned and continued on our way, taking in the breathtaking views before the descent. But perhaps that is enough for one post…


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