So close to the moon

The moon has influenced and fascinated humans ever since the year dot. It has been our constant companion, yet seemed out of reach – until that moment 50 years ago, when the first man set foot on the moon. Although Earth’s satellite has been conquered, surveyed and researched, it still puzzles us.

16 July 1969, 9:32 a.m. local time: with a roar reminiscent of a volcanic eruption, the Saturn V rocket lifts off from Kennedy Space Center in Florida with astronauts Neil Armstrong, Edwin E. Aldrin and Michael Collins on board. Their destination: the moon. The Apollo 11 mission marks the climax of the race into space between the USA and the Soviet Union. Just eight years earlier, President John F. Kennedy announced that the USA would put a man on the moon by the end of the decade. As the rocket takes off, however, nobody can say for certain whether this dream of mankind will actually be fulfilled.

Ever since time immemorial, the moon has exerted an irresistible pull on humans. It constantly changes shape: sometimes it appears as a barely visible crescent, then a round disc again, rising blood-red above the horizon on some nights, almost as if one can reach out and touch it. This spectacle already enchanted our ancestors, who marvelled at and worshipped Earth’s mysterious companion from afar. After all, the moon had the power to determine the fate of humans: it brought rain, enabled crops to grow and livestock to thrive; it made women fertile and watched over a safe birth. Just like the sun, the moon was also revered as a deity in many cultures. In Egypt and many other cultures, the moon was an important timekeeper, dictating the rhythm of life. In ancient Babylon, the Sumerians had lunar calendars over 4,000 years ago. These calendars helped determine the time to sow and the time to harvest. The lunar calendar still influences Jewish culture to this day.

The moon often inspired artists and poets, too. The most famous example from the modern age is probably the lullaby The Moon Has Risen by Matthias Claudius. Earth’s satellite was particularly a popular motif in poems from the Romantic period, representing yearning and unrequited love.Click to tweet It offered solace to lonely hearts, was a friend and loyal companion, and bathed the cares of the day in a mellow light. The moon frequently appears in pictures and graphic works, sometimes in its true form, sometimes personified as a deity, as in the engraving The Chariot of the Moon by Claude Mellan from 1633.

The moon was also portrayed caught between art and science in the special exhibition Fly Me to the Moon at Kunsthaus Zürich 1 , which also features loans from ETH Library, including old and rare books and a “tellurium” from the 19th century – an astronomical model which depicts the sun, Earth and moon along with their trajectories.

In a video interview, the curator of the exhibition, Cathérine Hug, describes what links art and the moon.

20 July 1969, four days and around four hours after lift-off: the Apollo 11 astronauts have entered the moon’s orbit. The landing module Eagle with Armstrong and Aldrin on board gradually disengages from the spaceship. They gaze spellbound out of the windows as they approach the surface of the moon. However, the automatically controlled descent does not go according to plan: the scheduled landing site is covered in boulders; it would be too risky to touch down. Armstrong spontaneously switches to manual controls and looks for a suitable spot to land. The tension rises at ground control in Houston: there is only enough fuel for one landing manoeuvre – it’s now or never.

Not in their wildest dream could astronomers over 500 years ago have imagined that humans would one day see the moon’s surface at close quarters. They observed the moon from afar on Earth – with the naked eye. While the details were not visible, astronomers were able to predict the trajectories of Earth’s satellite and lunar eclipses extremely accurately. For instance, the German astronomer Johannes Müller, later known as Regiomontanus, published Calendarium 2 in around 1472, a calendar with positional calculations for the sun and moon for the years 1475 to 1531. The work, a copy of which is owned by ETH Library, contains tables and simple drawings. At the time, drawings of the world mainly served as illustrations, but were not topographically accurate.

This all changed with the invention of the telescope in 1608, which took humans a sizeable step closer to the moon – optically speaking, at least. Suddenly, astronomers could see that the surface was richly textured and composed of craters and mountains. Galileo Galilei was one of the first to produce detailed drawings of the moon’s surface, which he published in 1610 in his work Sidereus nunciusClick to tweet 3 (The Starry Messenger in English). Thanks to the telescope, Galileo observed around ten times more stars than with the naked eye. And he discovered that other planets in the solar system besides Earth also have moons: no fewer than four were orbiting Jupiter. Although 75 other moons of Jupiter have been discovered to date, the four Galilean ones are by far the largest. 4

Almost simultaneously, in 1614, the German astronomer Johann Georg Locher and his tutor Christoph Scheiner published Disquisitiones mathematicae 5 . Although the lunar maps in this work were rougher than Galileo’s, the location and size of the “maria” (lunar seas) were more accurate. This is what the dark patches on the surface of the moon were dubbed in early lunar research as they were actually thought to be seas. Today, we know that these areas are basins caused by massive meteorite impacts during the early genesis of the moon. They were filled with lava, which poured out from inside the moon and have a different rock composition compared to the light plateaus. 6

Nearly 200 years later, photography constituted a major breakthrough in lunar observation. It superseded the painstaking drawings made on the telescope and opened up fresh possibilities for researching Earth’s satellite. From 1864 the American Lewis Morris Rutherford, a pioneer of astrophotography, published photographs of the moon he had taken from the garden at his house in New York. 7 A photograph from 8 March 1865 8 , a print of which ETH Library owns, is considered the best moon picture of the time.

The holdings of ETH Library also contain a systematic map of the moon’s surface based on photographs published by Claude Le Morvan in 1914. 9

Merely a few decades later – thanks to major technical advances – there was a shift from pure observation to actual exploration: after the first rockets were launched into space in the late 1940s, the first terrestrial flying object, the Soviet probe Luna 2, reached the surface of the moon in 1959.Click to tweet Suddenly, a voyage to the moon seemed within reach. Luna 2 was followed by further Soviet and, later, American space probes, which took photographs, shot film footage or measured the moon’s magnetic field. The first soft landing succeeded in 1966 with Luna 9 – a crucial step on the path towards a manned mission.

20 July 1969, four days and over six hours after lift-off: a gasp of relief at ground control in Houston – the crew has pulled off the landing manoeuvre. The lunar landing module Eagle with Armstrong and Aldrin on board touches down safely on the surface. Shortly afterwards, the time has come: Neil Armstrong slowly descends the ladder in his bulky spacesuit. More than 500 million people worldwide are following the historic moment on their television sets. 10 They watch the first person step onto the surface of the moon and hear the now famous words:

"That's one small step for a man. One giant leap for mankind."Click to tweet

Aldrin soon follows suit. During their roughly two-and-a-half-hour moonwalk, the astronauts set up measuring equipment for scientific experiments, including a solar sail from the University of Bern and a seismometer to measure moonquakes. And they collect around 20 kilograms of moon rock to bring back to Earth.

A tiny piece of Apollo moon rock is on display at ETH Zurich’s Earth Science Research and Information Centre focusTerra.Click to tweet 11 Studies conducted on rock samples from the first and all subsequent Apollo missions and the Russian Luna space probes yielded key scientific findings. They found the first evidence that the moon – like Earth – is composed of a silicate mantle and an iron core. Moreover, the moon’s age could now be determined (see info box).

The new findings also influenced the art world – as Cathérine Hug highlights in an interview.

The Apollo samples also provide clues as to how Earth’s faithful companion must have formed. There are various theories on this, the most widely accepted today being the “giant impact hypothesis”.Click to tweet According to this theory, a celestial body roughly the size of Mars (measuring several thousand kilometres in diameter) – called Theia – slammed into the young Earth. The violent impact generated an enormous amount of heat. Debris was catapulted into space, initially forming a disc around Earth, from which the moon was eventually formed. Many observations and measurements support the theory – including the analyses conducted by Maria Schönbächler, a professor at ETH Zurich’s Institute of Geochemistry and Petrology. She recently studied the chemical element zirconium in probes from the Apollo missions using new methods. Earlier studies had already revealed that rocks from the Earth’s mantle and the moon exhibit an almost identical isotope composition. 12 They effectively have the same fingerprint and thus must have been formed from the same material. Schönbächler managed to confirm this with her zirconium analysis. She also studied lunar meteorites found on Earth. In a video interview, she explains why these are important for research and what she hopes for from future moon missions.

There are still many open questions regarding the origins of the moon that research is trying to answer. Maria Schönbächler’s group is currently studying how the magma inside the moon solidified into solid rock during the cooling phase. The group headed by ETH Zurich professor Max Schmidt at the Department of Earth Sciences is also looking to understand these processes. In the lab, the researchers recreate the conditions inside the moon at the time under high pressure and high temperatures. David Sollberger from ETH Zurich’s Institute of Geophysics is investigating another aspect of the moon: he has devised a new method to evaluate the recordings of moonquakes from the Apollo 17 mission. The technique helps obtain new insights into the structure of the moon’s interior.

Even though nobody has set foot on the moon since 1972 – when the sixth and final Apollo mission took place, it remains the most visited object in the solar system and the only one that humans have walked upon.Click to tweet This is illustrated by an overview of all the manned and unmanned space missions, which is on display in the special exhibition Expedition Solar System at ETH Zurich’s information centre focusTerra. 15

Now space travel has set its sights on Earth’s nearest neighbour again: several nations aim to resume manned missions, including the USA, China and Japan. The European Space Agency (ESA) is even working on plans for a moon village, where astronauts can stay for longer. And there is also the vision of mining the raw materials found on the moon – such as noble gases and rare metals – and bringing them back to Earth. However, this is unlikely to happen any time soon as moon landings are extremely expensive, technically challenging and often do not go as planned. The most recent example: an unmanned craft, which Israel dispatched to the moon in April 2019, crashed upon landing. Earth’s moon seems to be doing its utmost to reject any further advances by man – and keep some of its secrets just a little while longer.