The Moon
From ancient mystery, understanding gravity and developing rockets enabled human exploration. The Moon became a vivid study, a journey of knowledge continuing.
The story begins with the Moon as the oldest astronomic object known to man, its motion studied since prehistoric times. For centuries, its surface had been mapped in detail, but despite this, the Moon seemed to reach a "dead end" as far as human eyes were concerned. Astronomers viewed it as a world without change, where a single photograph through a good telescope would remain valid for countless years. So certain was this belief that for about a hundred years, professional astronomers largely ignored it, leaving its study to amateurs. Only a little over half of its surface was visible from Earth, the other side remaining an "eternal mystery".
But this was not the end of the story; it was merely a pause. The narrative picks up pace dramatically in 1957, when humans achieved a monumental feat: they broke the shackles of Earth's gravity by sending an artificial satellite into orbit. This event marked a turning point, leading to a rapid acceleration in lunar exploration. Just two years later, a rocket-powered vehicle was sent past the Moon, and by 1969, humanity had lifted itself a quarter of a million miles from Earth. Astonishingly, astronauts stepped out onto the lunar surface, leaving human footprints behind.
This era transformed the Moon from a "dead world" into one with "vigorous life" for study. Suddenly, entire books could be dedicated to selenography, the detailed description of the Moon’s surface, and selenology, the study of its structure and evolution. Although our knowledge is far from complete, we have learned "amazingly much," exceeding previous dreams.
The book, first written in "presatellite days," had to be extensively revised to include these new findings. The revised edition incorporates the latest data, right down to descriptions of the lunar soil felt by instruments controlled from Earth and under an astronaut's boot. The story of lunar investigation, the book suggests, is far from over; it will continue to unfold as human exploration persists, potentially leading to people living on the Moon and requiring further revisions of the book itself.
The narrative then delves into specific aspects of this scientific journey, exploring concepts that are foundational to understanding the Moon and space travel. It touches upon ancient legends, like the story of Chandrasekhar, "the carrier of the moon," contrasting them with our modern understanding of the Moon as a rocky body revolving around the Earth, illuminated by the sun. It explains phenomena like the Moon's phases, its rotation and revolution periods (synodic and sidereal months), and how we see more than half of its surface due to slight variations in its orbit and rotation.
A significant part of the story revolves around the fundamental force governing celestial motions: gravity, the great discovery attributed to Sir Isaac Newton. The narrative recounts the famous, perhaps apocryphal, tale of Newton, an apple, and the realization that the same force pulling objects to Earth also pulls the Moon, acting as an "invisible string". Newton's genius lay in comparing these forces and deducing that gravity decreases in inverse proportion to the square of the distance. This concept revolutionized astronomy, explaining why celestial bodies move in elliptical orbits with the larger body at one focus. The Moon's orbit is indeed an ellipse, with the Earth near one focus.
Gravity also explains the tides, primarily caused by the Moon's pull, though the sun also contributes. The explanation uses the analogy of movers stretching or squeezing a balloon to describe the differential gravitational forces on the Earth's oceans. Tides demonstrate the Moon's observable effect on our planet, though there are also much smaller tides in the solid Earth. Interestingly, the tidal interaction between Earth and Moon acts as "cosmic brakes," subtly slowing Earth's rotation and causing the Moon to slowly recede. This leads to speculative ideas about the Moon and Earth potentially being much closer or even part of a single body billions of years ago.
The book moves on to the description of the lunar surface itself – selenography. Early telescopic observations, starting with Galileo, revealed dark, smooth areas mistakenly called "seas" (maria) and brighter, mountainous regions dotted with crater-like features. We now know the "seas" are dry, level plains, and the Moon has no atmosphere noticeable from Earth. However, subtle measurements require special equipment.
The distinctive lunar craters are central to the surface story, ranging from vast structures hundreds of miles across down to microscopic pits. Their origin is a key scientific question. While tiny ones were likely formed by high-speed meteorite impacts, explaining the larger, complex craters remains a challenge, with theories involving both external impacts and internal lunar forces. The narrative highlights the complexity by noting differences between craters (some with central mountains, others without) and features like enigmatic rows of craters or river-like rilles that seem incompatible with the moon's lack of atmosphere and water. The rilles even prompt a reassessment of older calculations about the Moon's ability to retain an atmosphere, suggesting it might have held one for hundreds of millions or even billions of years. This opens the door to fascinating, albeit speculative, possibilities, such as past water or even life on the Moon.
The story transitions from understanding the Moon to the long-held human dream of travelling to it. Early concepts, like Jules Verne's cannon, were imaginative but scientifically flawed compared to the actual requirements of space travel. The real challenge isn't just distance, but overcoming Earth's gravity well. This understanding relied on Newton's laws. Early ideas for propulsion were often unscientific. Even Verne, while relatively accurate for his time, made errors related to weightlessness and acceleration.
The story then culminates in the reality of moon rockets. Achieving moon flight wasn't just a matter of scientific theory, which was largely understood by Newton's time. It required enormous advancements in engineering, chemistry, metallurgy, and craftsmanship. The development of powerful liquid-fueled rockets, like the V-2, and crucial components such as high-performance fuel pumps were essential steps. The concept of the multiple-stage rocket became necessary because chemical fuels, while more energetic than gunpowder, still don't provide high enough exhaust velocities to escape Earth's gravity in a single stage.
Beyond rocketry, another critical piece of the puzzle was the development of the high-speed computer. Guiding a spacecraft on a trajectory where tiny errors early on can result in vastly different outcomes later requires rapid, complex calculations that were impossible before modern computers.
With the reality of moon landing achieved through Apollo missions, the story looks ahead. Future chapters involve establishing bases, potentially utilizing lunar resources like oxygen from rocks or possibly subsurface water. Such a base could support scientific exploration, perhaps uncovering clues about the Moon's origin and even the Earth's. The far side offers a unique location for radio telescopes, free from Earth's interference. Permanent residence could offer insights into biology and human physiology.
However, the book tempers future dreams with practicality. The Moon is unlikely to solve Earth's overcrowding or become a major source of raw materials due to the immense effort and cost of transportation. It is also deemed unsuitable as a military base. Instead, the primary return on this immense effort is knowledge. Reaching the Moon is presented as a proud human achievement, an act of mastery over the physical world, offering a better understanding of our own planet, our place in the universe, and our capabilities. The narrative concludes by stating that Chandrasekhar's lantern, the Moon, continues to serve as a guide.
In essence, the book tells the "story" of humanity's scientific and technological progression from distant, static observation of the Moon to its dynamic exploration and future possibilities, highlighting the key challenges and breakthroughs along the way – a journey very much in the spirit of Asimov's own explorations of science and the future. It's a story about how fundamental scientific laws, persistent curiosity, and incredible engineering come together to turn ancient myths and impossible dreams into tangible reality.
