In Paradiso, Canto II, Dante asks Beatrice about the Moon: “what are the dark marks on this planet’s body that there below, on earth, have made men tell the tale of Cain?”*
On Earth below, it is perhaps the brightness of the milk in the latte art that we notice in our coffee. But it is in fact precisely the contrast that we notice, both on the Moon and in our coffee.
What causes this contrast in the coffee and how does it link back to the Moon? Watching videos of, or if you are lucky to be close enough, baristas making latte art, you may be struck by the skill of the barista to form the milk into complex patterns and art. Swans, tulips and other designs appear on the surface of the drink with seemingly simple oscillations of the hand. And yet, if you’ve ever thought about attempting this art, you will appreciate how hard it is to design this contrast. How does the first pour of the milk lead to a significant uptake of the coffee (and hence a brown colouring), while the second part of the pour is dominated only by the milk and hence the shapes appear?
It must be partly a turbulence effect. The initial milk pour is from a significant height which would churn up the coffee meaning that the suspended particles in the coffee then get caught in the spaces between the bubbles in the milk’s microfoam. The second part of the pour is from a lower height which leads to a reduced mixing between the two liquids.
Yet this is only part of the story. Another perspective on it could be to consider the ‘albedo’ of the drink. The albedo is a measure of how reflective a surface is, so highly reflective surfaces (milk bubbles, ice sheets) have a higher albedo and less reflective surfaces (the coffee liquid, the earth’s surface) have a lower albedo. Part of the visibility of the latte art comes from this difference in reflectivity between the pattern part and the base part of the coffee.
In Earth science this has consequences for climate change: if the ice (high albedo, highly reflective) melts and reveals earth or sea (lower reflectivity, lower albedo), more sunlight is absorbed by the Earth and consequently you get local heating and locally accelerated ice melting. This may have consequences more globally in terms of climate change.
For Dante, it explained the colouration of the Moon. As his guide Beatrice explained to him: different parts of the Moon shone differently depending on their composition**.
Which takes us to another connection between science and art. It is recognised that, in European science history at least, Galileo first realised that the ‘dark marks’ on the Moon’s surface indicated that there were mountains and craters on the Moon. He was able to do this because he saw the Moon through a telescope and deduced that the patches were shadows. But when we think about this, it can’t be the whole story. While a telescope magnifies a distant object we still see, effectively, a 2D surface. We see the mountains on the Moon in the shadows because we know they are there. But how did Galileo know? Indeed, another astronomer at the same time was looking at the Moon through a telescope and could deduce only “strange spottedness”. What was the difference between Galileo and Thomas Harriot that allowed the former to see what the latter could not?
It has been suggested that it was Galileo’s artistic training that meant that he recognised the shades of light and dark as shadowsª. His practise at chiaroscuro drawing meant that he knew how to render depth using light and darkness in 2D images. When he saw the Moon, he could recognise the mountains. Another scientist, not familiar with how to render depth in painting, may instead see latte art on the Moon.
There are many ways in which our different backgrounds benefit each other and in which it benefits us to work as teams rather than individuals. There remain some though where the right combination of knowledge of both art and science combined with a particular skill at rendering them, can result in brilliant coffees, or astonishing discoveries, through connecting dots that otherwise could not be seen.
*The Divine Comedy, Dante Alighieri, Paradiso, Canto II. It is interesting here that Dante uses the word “planet” for the Moon, something that we would not do now. In a way it emphasises how our descriptive language changes with time and therefore how there may still be hope for Pluto’s rehabilitation.
** It is interesting here though that Beatrice’s answer to Dante is given to him only after she has convinced him through two experiments that his own explanation for the patches of the Moon was wrong.
ª Styles of Knowing, Chunglin Kwa, Pittsburgh Press, 2011