The Moon

by Oliver Morton

  † Until not that long before, it had been held that away from the shore, the Earth’s great ocean was higher than the land—hence the phrase “high seas”—but by Galileo’s day lowliness seemed strongly to suggest wateriness.

  * The International Astronomical Union, which takes care of such things, codified the remit of sea naming to characteristics of water and states of mind. When the Soviet Union was adamant that one of the seas its Luna 3 probe discovered on the far side was to be called Mare Moscoviense, diplomatic ingenuity allowed it on the basis that “Moscow is a state of mind”.

  * What of Galileo? Riccioli gave him a prominent feature, too, but later observers found that the feature named for him was not, in fact, a crater, but a ray-like patch of peculiar brightness: it is now called Reiner Gamma, in accordance with later rules of nomenclature. By the time this had been realized, all the big craters were named; the crater now called Galilei is anomalously, even embarrassingly, small. In recompense, though, the four largest moons of Jupiter, which Galileo discovered and named after the Medici family to gain patronage, are now known as the Galilean moons.

  * If so, they may have been in trouble, as Johann Andreas Schmidt, a Lutheran theologian, argued in “Selenitas e luna proscriptos divini numinis gratia” (1679; “Selenites, or the Moon proscribed by Divine Grace”). The Moon, he noted, was too inclement for vineyards, and without vineyards there could be no Communion, and thus no salvation. There could thus be no people with souls on the Moon, merely monsters.

  * Though gravitational force falls off with the square of distance, tidal effects fall off with the cube of distance, and 4003 is more than 30 million.

  * Later astronomers took this argument further, arguing that with a thin enough and stable enough lunar atmosphere, the star being transited would not be distorted, but its apparent position might change because of its light being refracted through that atmosphere. Sir George Airy, among others, looked for this phenomenon—and thus developed techniques which would in time be used to look for the effects of general relativity during solar eclipses and held up as the first confirming evidence of Einstein’s theory of general relativity.

  * The 21st-century account of this origin, complete with melted worlds, is found in Chapter IV.

  † Already an accepted notion among scientists of the time, though not under the same name as today.

  * Catharina is notable for being one of fewer than 30 lunar craters, out of over 1,600 with names, to be named in honour of a woman, in this case Saint Catherine of Alexandria.

  * The French astronomer, artist and illustrator Lucien Rudaux (1874–1947) is a notable exception.

  * Why is Mare Orientale in the west? On Earth, the direction in which the planet is spinning and the direction in which the night-edge is moving are opposed to one another; the planet spins to the east, and the night-edge moves to the west. On the Moon, the two directions are the same. Early astronomers defined the direction in which the Moon was spinning as being its east and, according to that convention, Mare Orientale is appropriately named. But that convention has the night-edge moving east, too, which freaks out today’s Moon scientists and astronauts: the Sun really should not rise in the west. So, they flipped the definitions of east and west, leaving Mare Orientale ill named.

  ITS ORBIT

  FROM THE EARTH TO THE MIDDLE OF THE NEARSIDE—ITS CLOSEST point and thus, because its mappers are of an Earthly bent, home to its prime meridian—is a distance about 60 times the radius of the Earth. If the Earth were the size of your head, the Moon would be a smallish apple on the other side of your living room.

  The exact distance can be as much as 398,600km or as little as 348,400km, because the Moon’s orbit is an ellipse, not a circle. As a result, its apparent size, as seen from the Earth, also varies: bigger when closer. When it is at its closest—a condition called perigee—the Moon can look as much as 14% larger than when it is at its farthest (apogee). Full Moons which coincide with perigee have come to be known as supermoons and can be up to 30% brighter than other full Moons.

  The plane of its orbit is not the same as the plane in which the Earth orbits the Sun, which is called the ecliptic; if the two planes were the same, every new Moon would eclipse the Sun as the three bodies lined up precisely. But the Moon’s orbit does cross the ecliptic—the points where it does so are called the nodes—and if the Moon is full or new when it reaches one of those nodes, observers on Earth will see an eclipse. If the Moon is new, it will be an eclipse of the Sun. If the Moon is full, the Earth’s shadow creates a lunar eclipse.

  Though the Moon’s orbital plane is not the same as the ecliptic, the angle between the two is small. This means that the Moon’s path through the Earth’s sky, like that of the Sun, changes with the seasons. In winter, when the Earth is leaning away from the Sun, both the Sun and the new Moon stay lower in the sky than they do in summer; the full Moon, opposite the Sun, rises higher and stays up longer. Above the Arctic Circle the winter Moon can stay up for more than 24 hours at a time, just as the summer Sun can. A scientist in Spitsbergen once told me that the midnight Sun is not as special to him as the noontime full Moon.

  As the Moon travels round the Earth, it moves with respect to the fixed stars behind it. Because its path is quite like the Sun’s, its circuit mostly passes through the signs of the zodiac (which are defined by the ecliptic). The Moon takes 27 days, 7 hours and 43 minutes to complete this circuit, a period of time called a sidereal month (from the Latin for “starry”, as in “Sidereus Nuncius”).

  The 12 constellations of the zodiac are not ideal for keeping track of the orbit of the Moon. Because it does not orbit exactly in the ecliptic it strays north and south of them a little; and 12 signs is not a handy way of dividing up a 27.3-day circuit. Chinese astrology instead divides the Moon’s path into 28 mansions.

  It is this movement against the background of the fixed stars that explains why the Moon rises a bit later every day. On the day that I am writing this, the Moon was in the mansion of the Net when it rose, which is defined by the star Epsilon Tauri; tomorrow it will have moved on to the mansion of the Turtle Beak, defined by Meissa, the star at the tip of Orion’s sword, which will rise about 50 minutes later.

  Just as the Earth must make more than one revolution to catch up with the moving Moon, so, because the Earth is moving round the Sun, the Moon must make more than one orbit round the Earth to get from one full Moon to the next. Imagine the Moon at the end of the minute hand of a clock centred on the Earth, and the Earth on the hour hand of a clock centred on the Sun. When both hands point the same way—let’s say at the nine—the Moon is full. An hour later the Moon will have made a complete circuit and be pointing at the nine again. But the Earth-hand, as it were, will have moved on to the ten with respect to the Sun. So it will be another five minutes before the hands line up again, with the Earth between Sun and Moon and the Moon back to its fullness. This longer period—29 days, 12 hours and 44 minutes—is called the synodic month.

  The synodic month is also the time that it takes the Moon to turn on its axis; that is why the nearside stays near and the farside, far. This is not a coincidence; it is an effect of the Earth’s gravity known as tidal locking. But the lock does not hold as tight as it might. There is some wriggle room. The Moon rotates at a constant speed. But the speed at which it moves in its orbit changes according to the laws Kepler laid down for elliptical orbits: at apogee it moves a touch slower; at perigee, a touch faster. So, near perigee, the Earth sees a little more of the Moon’s western hemisphere—because the Moon has got ahead, as it were—and at apogee, as it slows down, a little more of the eastern one. This “libration”—the effect that so interested William Gilbert, the first Moon mapper—means that if you watch the Moon closely enough for long enough, you will, over time, see rather more than half of it. Still, more than 40% of its surface is never seen from the Earth.

  Astronauts on the International Space Station are at times closer to the Moon than all the rest of
humankind. But just by a tenth of 1%. Only 24 men have, to date, gone closer than that.

  - III -

  APOLLO

  I THINK, THOUGH I CANNOT SAY FOR SURE, THAT GENE SHOEMAKER was the first human being to know that he could, that he should and that he very well might walk on the Moon.

  It was 1948, the summer after his graduation, and he was doing fieldwork in Arizona, camping under the stars. His alumni newsletter included a story about Caltech researchers experimenting with captured German V-2 rockets a few hundred kilometres to the east of him, at White Sands in New Mexico. With that news to hand, he saw the double nature of the Moon as no one had ever done before; he saw a place, sickle sharp in the high, clear sky, where a man like him might walk and work.

  “We’re going to explore space,” he later remembered thinking, “and I want to be part of it! The Moon is made of rock so geologists are the logical ones to go there—me, for example!” It was to make himself the logical choice that he became the world’s greatest expert on cratering; it was also the reason he created the US Geological Survey’s astrogeology programme.

  Two decades later, on a bright Florida morning, a cylinder of thin ice the size of a grain silo hung suspended tens of metres above the ground. The frost had started forming in the middle of the floodlit night, when the technicians at Cape Kennedy had started to fill the great tank at the top of the Saturn V’s first stage with liquid oxygen—more than a million litres of it, at a temperature of minus 183°C. The wall of the tank and the skin of the rocket were one and the same, so water vapour from the humid Atlantic air had immediately started to freeze to the painfully cold metal.

  As the oxygen was pumped in, some of it boiled off; vents at the top of the tank let the vapour out so that pressure within would not get too high. At 09:30, the vents were closed. Helium was pumped into the small space at the top of the tank. The pressure started to rise.

  Below the oxygen tank was a slightly smaller tank filled with highly refined kerosene. Below that, arranged like the dots on the five face of a die, were the F-1 engines, exquisitely engineered, cunningly contrived, ludicrously powerful.

  Two minutes after the vents were sealed, a valve at the bottom of the upper tank opened, and oxygen began to flow down into the F-1s. It took two different routes. Some of it went into gas generators which were linked to turbines which drove pumps. In the generators, it was mixed with kerosene and sparked alight. There was too much kerosene for the not-yet-full flow of oxygen to consume it all; the hot exhaust that the generators passed to the turbines was dirty black with part-burnt fuel. That didn’t stop it from spinning them up and bringing the engines’ pumps to life.

  The rest of the oxygen went into the combustion chambers proper. There it met the kerosene-rich exhaust coming out of the turbines, and the mixture was set alight all over again. Black smoke began to billow from the bottom of the F-1s’ nozzles. The rocket began to shake. The pumps increased the flow of fuel and oxygen down into the fires below.

  A carefully choreographed dance of temperature and energy was now under way. The turbopumps used energy from the fuel burned in the generators to get ever more fuel into the combustion chambers, but they sent it there by way of a spiralling detour through tubes wrapped around the engines’ nozzles. This cooled the nozzles, which otherwise could not have borne the heat they were subjected to. It also warmed the fuel, which thus burned even better when, at last, it reached the combustion chamber. The fuel was also the lubricant for many of the engines’ moving parts—and the soot produced early on gave the lower section of the nozzle more protection from the heat of the growing flame within.

  The pumps spun harder; the dance sped up. Five seconds after ignition, the fuel valves were fully open, and within a second or so the engines were close to full thrust. The central engine came to full power first, then the four outer ones. The fuel mix was now richer in oxygen, the burn cleaner and less sooty, more powerful. For a second or two after the last engine came up, the rocket was held down by mighty clamps. Then it was released.

  All the weight of the mighty first stage, of the propellant-filled second and third stages and of the Eagle, the Columbia and its service module right at the top—almost 3,000 tonnes in all—now rested on the engines. They shouldered their burden and began to lift. The five arms from the tower that steadied and fed the rocket swung back. The shell of ice that had clung to the supercool metal fell in shattered sheets into the inferno below.

  The fires on which it rose were not the fire that leaps or licks or plays, the fire of brasier or boiler. They were the focused fire of the metalworker’s torch, given life at a scale to cut worlds apart or weld them together. The temperature in the chambers was over 3,000°C. The pressure was over 60 atmospheres. And still the pumps, their turbines spinning 90 times a second, were powerful enough to cram more and more oxygen and fuel into the inferno. The flames slammed into the fire pits below at six times the speed of sound. For a couple of minutes, the five F-1s generated almost 60 gigawatts of power. That is equivalent to the typical output of all Britain’s electric-power plants put together.

  It took ten seconds for the rocket to clear the tower. It took a further ten seconds for the roar of its engines, louder than any noise humans had made before, to reach the VIP stands almost 6km away. Sixty ambassadors, half of Congress and about a quarter of America’s governors, watching with awe, shaken by “a sound that became your body”, as the artist Robert Rauschenberg put it.

  The roar lasted less than three minutes. But by the time the F-1s fell silent, the rocket was travelling at over 8,000kph and was 600km from Cape Kennedy. Apollo 11 was on its way to the Moon.

  Gene Shoemaker was not aboard. He had not been able to become an astronaut; Addison’s disease had put paid to the Moonshaker’s dreams of being a Moonwalker. The astrogeology programme that he had created, though, shaped where the astronauts would go on the Moon and what they would do there. It had trained all three of the men flying off over the Atlantic that morning, and all their successors, too.

  Shoemaker could have had an honoured seat in the VIP stands. But he and his wife, Carolyn, were rafting down the Colorado River.

  THE V-2S THAT SHOEMAKER HAD READ ABOUT IN HIS ALUMNI newsletter started as inaccurate terror weapons. They killed thousands in Belgium and Britain. The death toll among the concentration camp slaves in the factories where they were built was even higher.

  The men who designed and built them had come, earlier than Shoemaker, to believe that space travel was a real possibility. Many of them had been members of the Verein für Raumschiffahrt (VfR), an association of German rocketry enthusiasts inspired by the ideas of Hermann Oberth, as set forth in his book “Die Rakete zu den Planetenräumen” (1923; “The Rocket into Planetary Space”). Some of them went on to work on the Saturn Vs that took Americans to the Moon.

  Oberth, a physicist and engineer originally from Transylvania, was one of a trio of early visionaries who believed both in the goal of space travel and in a specific technology that would deliver it: the liquid-fuelled rocket. Rockets of the sort first developed in China, used for both celebration and warfare across Eurasia since the Middle Ages, burn a solid fuel, such as gunpowder, to produce hot, expanding vapours. Expelled backwards, the gases drive the projectile forwards.

  As a use of gunpowder, such rockets were rarely preferred to guns themselves: the hot, expanding gases provided kinetic energy more effectively when confined by a metal barrel so as to expel a small projectile in a reasonably predictable direction. But the preference was not universal. The Kingdom of Mysore in India pioneered the craft of making the rockets themselves from metal.

  The British, having found themselves on the receiving end of this weaponry, liked the rockets’ rate of fire and portability, when compared to cannon. They applied the new metalworking skills of the industrial revolution to improving the technology; their rockets’ red glare over Fort McHenry, Maryland, was soon commemorated in America’s national anthem for its frighte
ning drama, if also for its lack of effect. In 1861, four years before Jules Verne used a gun to send his travellers to the Moon, a Scottish astronomer called William Leitch suggested that rockets might fulfil the same office.

  Rockets, yes. Solid rockets, no. The gunpowder used in rocketry is a mixture of fuel—sulphur and charcoal—and oxidant—potassium nitrate, also known as saltpetre. It is the fact that the fuel reacts with an oxidant readily to hand, rather than needing air, that makes gunpowder a useful explosive. But the rate at which the explosion can take place is limited by the speed that the explosion moves through the gunpowder. In a liquid-fuelled rocket, the fuel and the oxidant can burn as quickly as you can pump them together. It was a Russian physicist, Konstantin Tsiolkovsky, who first showed that a rocket which used liquid hydrogen as a fuel and liquid oxygen as an oxidant could, if built of multiple stages, attain a speed of 8km/s, enough in principle to put it in orbit round the Earth.

  This was not, to Tsiolkovsky, a mere fact of engineering. To attain orbit was the most important thing any machine could do. Like most speculative thinkers of his day, Tsiolkovsky, one of a group of Russian thinkers known as “Cosmists”, was seized by the importance of evolution. But he did not look to space, as James Nasmyth did, to understand the past evolution of planets, but to permit the future evolution of people. He saw space-based evolution in terms of the perfection of humanity, the realm in which life could become carefree and immortal, illuminated by endless cosmic energy.

  Oberth built on Tsiolkovsky’s research, as did Robert Goddard in America. Both men were, like their Russian inspiration, seized by the possibility that humans could travel beyond the Earth, though they tended not to express themselves on the matter as mystically as Tsiolkovsky did. They also knew they faced daunting technological challenges, such as storing and pumping liquid oxygen and crafting combustion chambers and exhaust nozzles which could withstand uncommon pressures and temperatures. Solving these would require years or decades of expensive research. There were applications beyond, or perhaps before, spaceflight: rockets might be a way of delivering emergency supplies, and maybe even first-class mail, to otherwise hard-to-reach places—the delivery drones of their day. Oberth gave lectures on such possibilities. But, in his memoirs, Willy Ley, vice president of the VfR, recalled a conversation with the older man after a lecture in the late 1920s: