Archaeoastronomy and cultural astronomy are often considered synonyms, but they actually express different concepts, the former being a sub-discipline of the latter. Cultural astronomy is a fascinating but controversial discipline, which serves as an auxiliary subject to social sciences such as history, archaeology, anthropology, and ethnography, among others. The tools and methodology of astronomy play a relevant role in the discipline, but it should be inserted within social sciences epistemology.
Juan Antonio Belmonte
Astrobiology seeks to understand the origin, evolution, distribution, and future of life in the universe and thus to integrate biology with planetary science, astronomy, cosmology, and the other physical sciences. The discipline emerged in the late 20th century, partly in response to the development of space exploration programs in the United States, Russia, and elsewhere. Many astrobiologists are now involved in the search for life on Mars, Europa, Enceladus, and beyond. However, research in astrobiology does not presume the existence of extraterrestrial life, for which there is no compelling evidence; indeed, it includes the study of life on Earth in its astronomical and cosmic context. Moreover, the absence of observed life from all other planetary bodies requires a scientific explanation, and suggests several hypotheses amenable to further observational, theoretical, and experimental investigation under the aegis of astrobiology. Despite the apparent uniqueness of Earth’s biosphere— the “n = 1 problem”—astrobiology is increasingly driven by large quantities of data. Such data have been provided by the robotic exploration of the Solar System, the first observations of extrasolar planets, laboratory experiments into prebiotic chemistry, spectroscopic measurements of organic molecules in extraterrestrial environments, analytical advances in the biogeochemistry and paleobiology of very ancient rocks, surveys of Earth’s microbial diversity and ecology, and experiments to delimit the capacity of organisms to survive and thrive in extreme conditions.
Astrology in Ancient Greek and Roman Culture
Astrology was a central feature of Greek and Roman culture. A knowledge of astrology’s claims, practices, and world view is essential for a full understanding of religion, politics, and science in the Greek and Roman worlds. Astrology is the name given to a series of diverse practices based in the idea that the stars, planets, and other celestial phenomena possess significance and meaning for events on Earth. It assumes a link between Earth and sky in which all existence, spiritual, psychological, and physical, is interconnected. Most premodern cultures practice a form of astrology. A particularly complex variety of it evolved in Mesopotamia in the first and second millennia bce from where it was imported into the Hellenistic world from the early 4th century bce onward. There it became attached to three philosophical schools, those pioneered by Plato, Aristotle and the Stoics, all of which shared the assumption that the cosmos is a single, living, integrated whole. Hellenistic astrology also drew on Egyptian temple culture, especially the belief that the soul could ascend to the stars. By the 1st century ce, the belief in the close link between humanity and the stars had become democratized and diversified into a series of practices and schools of thought which ranged across Greek and Roman culture. It was practiced at the imperial court and in the street. It could be used to predict individual destiny, avert undesirable events, and arrange auspicious moments to launch new enterprises. It could advise on financial fortunes or the condition of one’s soul. It was conceived of as natural science and justified by physical influences or considered to be divination, concerned with communication with the gods and goddesses. In some versions, the planets were neither influences nor causes of events on Earth, but timing devices, which indicated the ebb and flow of human affairs, like the hands on a modern clock. Astrology had a radical view of time in which the future already existed, at least in potential, and the astrologer’s task was to intercede in time, altering the future to human advantage. In this sense astrology was a form of “participation mystique” in which time and space were conceived of as a single entity and individual and social benefits were to be derived from engaging with it. There was no one single version of astrology and there were disputes about what it was and what it could do, for example, whether it could make precise predictions about individual affairs or merely general statements. From the early 4th century it went into a progressive decline, facing challenges from Christianity and the fragmentation of classical culture, especially in Western Europe. It survived in Persia, exerted a powerful influence on Indian astrology, and was transmitted to the Islamic world, from where it was reimported into the Latin West in the 12th century.
Composition of Earth
Early models of the composition of the Earth relied heavily on meteorites. In all these models Earth had different layers, each layer corresponded to a different type of meteorite or meteorite component. Later, more realistic models based on analyses of samples from Earth began with Ringwood’s pyrolite composition in the 1960s. Further improvement came with the analyses of rare MgO rich peridotites from a variety of occurrences all over the Earth, as xenoliths enclosed in melts from the upper mantle or as ultramafic massifs, tectonically emplaced on the Earth’s surface. Chemical systematics of these rocks allow the determination of the major element composition of the primitive upper mantle (PUM), the upper mantle after core formation and before extraction of basalts ultimately leading to the formation of the crust. Trace element analyses of upper mantle rocks confirmed their primitive nature. Geochemical and geophysical evidence argue for a bulk Earth mantle of uniform composition, identical to the PUM, also designated as “bulk silicate Earth” (BSE). The formation of a metal core was accompanied by the removal of siderophile and chalcophile elements into the core. Detailed modeling suggests that core formation was an ongoing process parallel to the accretion of Earth. The composition of the core is model dependent and thus uncertain and makes reliable estimates for siderophile and chalcophile element concentrations of bulk Earth difficult. Improved stable isotope analyses show isotopic similarities with noncarbonaceous chondrites (NCC), while the chemical composition of the mantle of the Earth indicates similarities with carbonaceous chondrites (CC). In detail, however, it can be shown that no single known meteorite group, nor any mixture of meteorite groups can match the chemical and isotopic composition of Earth. This conclusion is extremely important for any formation model of the Earth.
Condensation Calculations in Planetary Science and Cosmochemistry
Denton S. Ebel
The Sun’s chemical and isotopic composition records the composition of the solar nebula from which the planets formed. If a piece of the Sun is cooled to 1,000 K at 1 mbar total pressure, a mineral assemblage is produced that is consistent with the minerals found in the least equilibrated (most chemically heterogeneous), oldest, and compositionally Sunlike (chondritic), hence most “primitive,” meteorites. This is an equilibrium or fractional condensation experiment. The result can be simulated by calculations using equations of state for hundreds of gaseous molecules, condensed mineral solids, and silicate liquids, the products of a century of experimental measurements and recent theoretical studies. Such calculations have revolutionized our understanding of the chemistry of the cosmos. The mid-20th century realization that meteorites are fossil records of the early solar system made chemistry central to understanding the origin of the Earth, Moon, and other bodies. Thus “condensation,” more generally the distribution of elements and isotopes between vapor and condensed solids and/or liquids at or approaching chemical equilibrium, came to deeply inform discussion of how meteoritic and cometary compositions bear on the origins of atmospheres and oceans and the differences in composition among the planets. This expansion of thinking has had profound effects upon our thinking about the origin and evolution of Earth and the other worlds of our solar system. Condensation calculations have also been more broadly applied to protoplanetary disks around young stars, to the mineral “rain” of mineral grains expected to form in cool dwarf star atmospheres, to the expanding circumstellar envelopes of giant stars, to the vapor plumes expected to form in giant planetary impacts, and to the chemically and isotopically distinct “shells” computed and observed to exist in supernovae. The beauty of equilibrium condensation calculations is that the distribution of elements between gaseous molecules, solids, and liquids is fixed by temperature, total pressure, and the overall elemental composition of the system. As with all sophisticated calculations, there are inherent caveats, subtleties, and computational difficulties. In particular, local equilibrium chemistry has yet to be consistently integrated into gridded, dynamical astrophysical simulations so that effects like the blocking of light and heat by grains (opacity), absorption and re-emission of light by grains (radiative transfer), and buffering of heat by grain evaporation/condensation are fed back into the physics at each node or instance of a gridded calculation over time. A deeper integration of thermochemical computations of chemistry with physical models makes the prospect of a general protoplanetary disk model as hopeful in the 2020s as a general circulation model for global climate may have been in the early 1970s.
Depictions of the Moon in Western Visual Culture
Jay M. Pasachoff and Roberta J.M. Olson
Since the landmark lunar landing of Apollo 11 on July 20, 1969, NASA’s Lunar Reconnaissance Orbiter (launched in 2009), and the Japanese Aerospace Exploration Agency’s Kaguya spacecraft (2007–2009), among other efforts, have now mapped the Moon’s surface. Before those technological advances and since the beginning of recorded time, people and civilizations have been entranced by Earth’s only natural satellite, which is the second-brightest celestial object visible in the sky from the surface of the planet. Selected examples, among thousands, show how the history of the Moon has been regarded, illustrated, and mapped in visual culture in the Western world. Early examples include representations of a formulaic crescent Moon in Babylonian times; later this dominant stylized depiction of the Moon gave way to more naturalistic images based on observation, culminating in Leonardo da Vinci’s manuscript drawings, which study the lunar structure and cratered surface, and Galileo Galilei’s first telescopic images of the Moon recorded in wash drawings and woodcuts for his book Sidereus Nuncius. Both the artistic and scientific visual acuity that made this evolution possible belonged to the burgeoning empiricism of the 14th through the 17th centuries, which eventually yielded modern observational astronomy and impacted lunar iconography. The subsequent dramatic mapping of the Moon’s surface and the naming of its features became a preoccupation of many astronomers and some artists, who assisted scientists in illustrating their work. With the seeming physical mapping of the Earth-facing side of the Moon well underway in the late 18th and early 19th centuries, the function of Earth’s satellite as a Romantic symbol gained force in the all the arts but most dramatically in the works of landscape painters in Germany (e.g., Caspar David Friedrich and Carl Gustav Carus) and in England (e.g., Samuel Palmer). At the same time, William Blake, who was obsessed with astronomical imagery, used the Moon for expressive purposes, which reached a fever pitch later in the century in the work of Vincent Van Gogh. Along with the increasing accuracy of the Moon’s portrayal through both artists’ and scientists’ representations, the dramatic history of its mapping from Earth crescendoed with the development of photography and William Cranch Bond’s first successful daguerreotype of the Moon in 1851. Further exploration of the Moon, including its far side, has gravitated to aerospace engineers in cooperation with physicists, astronomers, mathematicians, and Apollo astronauts. Nevertheless, the Moon has remained an enduring object of fascination for artists—among the many, Surrealist Joan Miró, Veja Celmins, and Andy Warhol.
Ethics of Planetary Science and Exploration
Since the launch of Sputnik on October 4, 1957, the development of space activities has provided a kind of evidence for the conduct of human affairs, to the point of neglecting to question these activities from an ethical point of view: only since the beginning of the 2000s has a real ethical interrogation within the space community (French Space Agency, International Space University, COPUOS) been developed, in parallel with international law. Taking advantage of a rich cultural background and a cooperative sustained effort, space ethics contributes, for example, to better management of debris orbiting the Earth, evaluation of the social impacts of observation satellite systems, and the arrival of new private entrepreneurs apparently less aware of the impacts of managing space as a common heritage of humanity. If space law provides a possible framework and a set of principles for the current and future management of space activities, ethical principles must be considered to accurately assess their reasons for being and their consequences. The following questions are pertinent today: Has space become a trash can? Is space “Big Brother’s” ally? Is space for sale? Should space be explored at any cost? These issues require special expertise of the situation (e.g., the distribution of debris around the Earth, the capabilities of observation satellites); consideration of the global, dual (civil, military) nature of space; and reference to ethical principles (responsibility, vigilance). Human space flight, space tourism, and the search for extraterrestrial life are also subject to ethical questioning. At the beginning of the 21st century, space ethics remained a goal for the space community.
The Formation of the Martian Moons
Pascal Rosenblatt, Ryuki Hyodo, Francesco Pignatale, Antony Trinh, Sebastien Charnoz, Kevin Dunseath, Mariko Dunseath-Terao, and Hidenori Genda
The origin of the natural satellites or moons of the solar system is as challenging to unravel as the formation of the planets. Before the start of the space probe exploration era, this topic of planetary science was restricted to telescopic observations, which limited the possibility of testing different formation scenarios. This era has considerably boosted this topic of research, particularly after the Apollo missions returned samples from the Moon’s surface to Earth. Observations from subsequent deep space missions such as Viking 1 and 2 Orbiters, Voyager 1 and 2, Phobos-2, Galileo, Cassini-Huygens, and the most recent Mars orbiters such as Mars Express, as well as from the Hubble space telescope, have served to intensify research in this area. Each moon system has its own specificities, with different origins and histories. It is widely accepted that the Earth’s Moon formed after a giant collision between the proto-Earth and a body similar in size to Mars. The Galilean moons of Jupiter, on the other hand, appear to have formed by accretion in a circum-Jovian disk, while smaller, irregularly shaped satellites were probably captured by the giant planet. The small and medium-sized Saturnian moons may have formed from the rings encircling the planet. Among the terrestrial planets, Mercury and Venus have no moons, the Earth has a single large moon, and Mars has two very small satellites. This raises some challenging questions: What processes can lead to moon formation around terrestrial planets and what parameters determine the possible outcomes, such as the number and size of moons? The answer to such fundamental questions necessarily entails a thorough understanding of the formation of the Martian system and may have relevance to the possible existence of (exo)moons orbiting exoplanets. The formation of such exomoons is of great importance as they could influence conditions for habitability or for maintaining life over long periods of time on the surface of Earth-like exoplanets, for example by limiting the variations of the orientation of the planet’s rotation axis and thus preventing frequent changes of its climate. Our current knowledge concerning the origin of Phobos and Deimos has been acquired from observational data as well as theoretical work. Early observations led to the idea that the two satellites were captured asteroids but this created difficulties in reconciling the current orbits of Phobos and Deimos with those of captured bodies, hence suggesting the need for an alternative theory. A giant-impact scenario provides a description of how moons similar to Phobos and Deimos can be formed in orbits similar to those observed today. This scenario also restricts the range of possible composition of the two moons, providing a motivation for future missions that aim for the first time to bring material from the Martian system back to Earth.
Kun Wang and Randy Korotev
For thousands of years, people living in Egypt, China, Greece, Rome, and other parts of the world have been fascinated by shooting stars, which are the light and sound phenomena commonly associated with meteorite impacts. The earliest written record of a meteorite fall is logged by Chinese chroniclers in 687 bce. However, centuries before that, Egyptians had been using “heavenly iron” to make their first iron tools, including a dagger found in King Tutankhamun’s tomb that dates back to the 14th century bce. Even though human beings have a long history of observing meteors and utilizing meteorites, we did not start to recognize their true celestial origin until the Age of Enlightenment. In 1794 German physicist and musician Ernst Chladni was the first to summarize the scientific evidence and to demonstrate that these unique objects are indeed from outside of the Earth. After more than two centuries of joint efforts by countless keen amateur, academic, institutional, and commercial collectors, more than 60,000 meteorites have been catalogued and classified in the Meteoritical Bulletin Database. This number is continually growing, and meteorites are found all over the world, especially in dry and sparsely populated regions such as Antarctica and the Sahara Desert. Although there are thousands of individual meteorites, they can be handily classified into three broad groups by simple examinations of the specimens. The most common type is stony meteorite, which is made of mostly silicate rocks. Iron meteorites are the easiest to be preserved for thousands (or even millions) of years on the Earth’s surface environments, and they are composed of iron and nickel metals. The stony-irons contain roughly the same amount of metals and silicates, and these spectacular meteorites are the favorites of many collectors and museums. After 200 years, meteoritics (the science of meteorites) has grown out of its infancy and become a vibrant area of research today. The general directions of meteoritic studies are: (1) mineralogy, identifying new minerals or mineral phases that rarely or seldom found on the Earth; (2) petrology, studying the igneous and aqueous textures that give meteorites unique appearances, and providing information about geologic processes on the bodies upon which the meteorites originates; (3) geochemistry, characterizing their major, trace elemental, and isotopic compositions, and conducting interplanetary comparisons; and (4) chronology, dating the ages of the initial crystallization and later on impacting disturbances. Meteorites are the only extraterrestrial samples other than Apollo lunar rocks and Hayabusa asteroid samples that we can directly analyze in laboratories. Through the studies of meteorites, we have quested a vast amount of knowledge about the origin of the Solar System, the nature of the molecular cloud, the solar nebula, the nascent Sun and its planetary bodies including the Earth and its Moon, Mars, and many asteroids. In fact, the 4.6-billion-year age of the whole Solar System is solely defined by the oldest age dated in meteorites, which marked the beginning of everything we appreciate today.
The Moon and Planets Among the Incas and Other Pre-Hispanic Andean Peoples
Although the Inca state (ca. 1200–1572 ce) was called the Empire of the Sun, the Moon was, in some respects, an equally important divinity in the official state cult. The regulatory function of the phases of the synodic cycle of the Moon in different kinds of social activities, especially those framed in calendrical systems but also military campaigns, is well documented. As far as the orientation of architectural structures is concerned, the researchers focus their attention almost entirely on the position of the Sun. However, a more accurate analysis of two well-known sites—the caves of Intimachay and Inkaraqay—may provide evidence of their function as observatories of the lunar 18.6-year cycle. Those results may confirm the hypothesis, presented some years ago, that the Incas had elaborated a rudimentary method of predicting lunar eclipses. The determination of the exact role of Venus and other planets in the Inca worldview encounters a serious limitation: in contrast to Mesoamerica, in Tahuantinsuyu and the Andes, there are no important “first-hand” sources such as the calendrical-astronomical data of the Maya or the Aztecs. Only Venus seems to have enjoyed a cult of Pan-American range. The morning appearance of Venus was apparently related to the puberty initiation rites of male adolescents, while its appearance as Evening Star seems to have been closely symbolically related to the Inca sovereign and his military activities. Putting aside the information available on Venus and its cult, there is an almost complete lack of data on the other planets. Another problem must be considered: To what extent did the Incas inherit their knowledge from their predecessors, the Chimus, or even earlier cultures?
The Moon and Planets in Ancient Mesopotamia
In ancient Mesopotamia, all five planets visible to the naked eye were known and studied, along with the Moon, the Sun, the stars, and other celestial phenomena. In all Mesopotamian sources concerning the Moon and the planets, be they textual or iconographical, the astronomical, astrological, and religious aspects are intertwined. The term “astral science” covers all forms of Mesopotamian scholarly engagement with celestial entities, including celestial divination and astrology. Modern research on Mesopotamian astral science began in the 19th century. Much research remains to be done, because important sources remain unpublished and new questions have been posed to published sources. From ca. 3000 bce onward, Mesopotamians used a calendar with months and years, which indicates that the Moon was studied at that early age. In cuneiform writing, the Sumerian and Akkadian names of the Moongod, Nanna/Sin, are attested since ca. 2500 bce. The most common Akkadian names of the five planets, Šiḫṭu (Mercury), Dilbat (Venus), Ṣalbatānu (Mars), White Star (Jupiter), and Kayyāmānu (Saturn), are attested first in 1800–1000 bce. The Moon, the Sun, and the planets were viewed as gods or manifestations of gods. From ca. 1800 bce onward, the phenomena of the Moon, the Sun, and the planets were studied as signs that were produced by the gods to communicate with humankind. Between ca. 600 bce and 100 ce, Babylonian scholars reported lunar and planetary phenomena in astronomical diaries and related texts. Their purpose was to enable predictions of the reported phenomena with period-based, so-called Goal-Year methods. After the end of the 5th century bce Babylonian astronomers introduced the zodiac and developed new methods for predicting lunar and planetary phenomena known as mathematical astronomy At about the same time they developed horoscopy and other forms of astrology that use the zodiac, the Moon, the Sun, and the planets to predict events on Earth.
The Moon and Planets in Indigenous California
Anthropologists distinguish the U.S. State of California as a primary zone of prehistoric and tribal North America—it was one of the most linguistically and cultural diverse regions on earth. The original population of Native California and traditional cultures were decimated by the Spanish, the Mexicans, and the Anglos, who successively settled California and transformed it. For that reason, knowledge of the character and function of astronomy in what is now California prior to European contact in the 16th century is incomplete and fragmented. Traditional astronomical lore is preserved in a few ethnohistoric commentaries, in some archaeological remains, and in ethnographic research conducted primarily in the early 20th century, when elements of indigenous knowledge still survived. Throughout Native California, the moon’s conspicuous brightness, movement, and systematically changing appearance prompted its affiliation with seasonal change, the passage of time, and cyclical renewal, and most California tribes monitored and counted lunations in one way or another, but not necessarily throughout the entire year. In some cases, individual lunations were affiliated with and named for seasonal circumstances. There is little evidence, however, for even minimal interest in or recognition of the planets visible to the unaided eye, with the exception of Venus as the “Morning Star” or “Evening Star.” Venus, like the moon and other celestial objects, was personified and regarded as a fundamental and active agent of the cosmos. There is no evidence, however, for detailed monitoring of Venus and quantitative knowledge of its synodic behavior.
The Planets in Aboriginal Australia
Duane W. Hamacher and Kirsten Banks
Studies in Australian Indigenous astronomical knowledge reveal few accounts of the visible planets in the sky. However, what information we do have tells us that Aboriginal people are close observers of planets and their motions and properties. Indigenous Australians discerned between planets and stars by their placement in the sky and their general lack of scintillation. Traditions generally describe the ecliptic and zodiac as a pathway of sky ancestors represented by the sun, moon, and planets. This included observing the occasional backwards motion of sky ancestors as they communicate with each other during their journey across the sky, representing an explanation of retrograde motion. Aboriginal and Torres Strait Islander people note the relative brightness of the planets over time and information about the roles they play in their traditions around Australia. Knowledge systems outline the importance placed on Venus as the morning and evening star, making connections to the object as it transitions form one to the other through observations and calculation of the planet’s synodic period. Traditions note the relative positions of the planets to the moon, sun, and background stars, as well as inter planetary dust through zodiacal light, which is perceived as a celestial rope connecting Venus to the sun. The relative dearth of descriptions of planets in Aboriginal traditions may be due to the gross incompleteness of recorded astronomical traditions and of ethnographic bias and misidentification in the anthropological record. Ethnographic fieldwork with Aboriginal and Torres Strait Islander communities is revealing new, previously unrecorded knowledge about the planets and their related phenomena.
The Planets in Alchemy and Astrology (Medieval and Renaissance)
In the Middle Ages and Renaissance, alchemy and astrology shared a common language in the meanings and characters attributed to the celestial bodies, which provided a cosmic framework for understanding all terrestrial affairs. Astrology is the name given to a series of diverse practices based in the idea that the stars, planets, and other celestial phenomena possess significance and meaning for events on the Earth. In practical terms, astrology’s function was to predict the future, manage the present, and understand the past. In the Middle Ages and Renaissance, these three functions were not seen as separate, because time existed as a single entity—past, present, and future coexisted in the mind of God. Astrology assumed a link between Earth and sky in which all existence, spiritual, psychological, and physical, is interconnected. Time and space existed in a mutually dependent continuum, in which both were infused with the same qualities, represented in terms of astrological language by zodiac signs and planets. The practice of alchemy applied such assumptions to the material world, attempting to convert one metal into another, typically lead into gold. As all things were interconnected, including soul and body, the physical practice of alchemy was intimately connected with spiritual practice intended to purify the soul in preparation for its meeting with the divine. The planets had roles in both astrology and alchemy. A planet, from the Greek planētai, meaning wanderer, is a star, a point, or source of light in the sky that constantly alters its position. This is in contrast to the so-called fixed stars, which appear to keep exactly the same position relative to each other, at least over historic periods of time. Technical astrology largely developed in the Hellenistic, Greek-speaking world from the early third century BCE onward. With the collapse of the Roman Empire and classical learning in most of Western Europe from the 5th century, the complex astrology of the Classical world largely disappeared. It returned to Western Europe in two phases. The first phase, mainly in the 12th century, included the translation into Latin of major texts from Arabic, including those originally composed in Greek, and was accompanied by Aristotelian works that justified the use of astrology in naturalistic terms, thereby negating Christian disapproval. Alchemy was introduced into Western Europe at the same time. The second phase began mainly in the 15th century, during the Renaissance, as part of a wider revival of Classical thought encouraged by the translation of Platonic, neo-Platonic, and Hermetic works from Greek directly into Latin. By the end of the 17th century, the practice of both astrology and alchemy had largely disappeared. Astrology was confined to popular almanacs and alchemy was replaced by modern chemistry.
Planets in Inuit Astronomy
Inuit are an indigenous people traditionally inhabiting the Arctic and sub-Arctic regions of Greenland, Canada, Alaska, and parts of Russia’s Chukchi Peninsula. Across this vast region, Inuit society, while not entirely homogeneous either culturally or linguistically, nevertheless shares a fundamental cosmology, in part based on a common understanding of the sky and its contents. Traditionally, Inuit used prominent celestial objects—the sun, moon, and major circumpolar asterisms—as markers for estimating the passage of time, as wayfinding and directional aids, and, importantly, as the basis of several of the foundational myths and legends underpinning their society’s social order and mores. Random inquiries on Inuit astronomy made by European visitors after initial contact through the mid-18th and early 20th centuries were characteristically haphazard and usually peripheral to some other line of ethnological enquiry, such as folklore or mythology. In addition, the early accounts of Inuit star lore were often prone to misrepresentation due to several factors, including European cultural bias, translation inadequacies, a deficiency of general astronomical knowledge on the part of most commentators, and, most significantly, a failure—sometimes due to lack of opportunity—to conduct systematic observations of the sky in the presence of Inuit knowledge holders. Early accounts therefore tended to diminish the cultural significance of Inuit astronomy, almost to the point of insignificance. Unfortunately, by the time systematic fieldwork began on the topic, in the mid-1980s, unalloyed information on Inuit astronomical knowledge was already elusive, more and more compromised by European acculturation and substitution and, notably, by light pollution—a consequence of the increasing urbanization of Inuit communities beginning in the late 1950s. For the residents of most Arctic settlements, street lights reflecting off the snow have virtually eliminated the evocative phenomenon of the “polar night.” For several reasons, the role of planets in Inuit astronomy is difficult to determine, due, in part, to the characteristics of the planets themselves. Naked-eye differentiation between the major visible planets is by no means straightforward, and for observers living north of the Arctic Circle, the continuous or semicontinuous periods of daylight/twilight obtaining throughout the late spring, summer, and early fall effectively prevent year-round viewing of the night sky, making much planetary movement unobservable, far less an appreciation of the planets’ predictable synodic and sidereal periods. Mitigating against the significant use of planets in Inuit culture is also the principle that their applied astronomy, along with its cosmology and mythologies depend principally on—apart from the sun and the moon—the predictability of the “fixed stars.” Inuit of course did see the major planets and took note of them when they moved through their familiar asterisms or appeared, irregularly, as markers of solstice, or harbingers of daylight after winter’s dark. Generally, however, planets seem to have been little regarded until after the introduction of Christianity, when, in parts of the Canadian eastern Arctic, Venus, in particular, became associated with Christmas. While there are anecdotal accounts that some of the planets, again especially Venus, may have had a place in Greenlandic mythology, this assertion is far from certain. Furthermore, reports from Alaska and Greenland suggesting that the appearance of Venus was a regular marker of the new year, or a predictor of sun’s return, need qualification, given the apparent irregularity of Venus’s appearances above the horizon. A survey of relevant literature, including oral history, pertaining either directly or peripherally to Inuit astronomical traditions, reveals few bona fide mention of planets. References to planets in Inuit mythology and astronomy are usually speculative, typically lacking supportive or corroborative information. It can therefore be reasonably inferred that, with the qualified exception of Venus, planets played little part in Inuit astronomy and cosmology despite their being, on occasion, the brightest objects in the Northern celestial sphere. This being the case, there is a certain irony in NASA’s recently bestowing Inuit mythological names on a group of Saturn’s moons—Saturn being a planet the Inuit themselves, as far as can be determined, did not note or recognize.
Records of Planetary Observations in Ancient Japan Before the 11th Century
Kiyotaka Tanikawa and Mitsuru Sôma
The records of planetary observations in Japan in the 7th century ad are treated separately from other records because they are written in the Nihongi. It is known that Japanese observational astronomy was recorded in the 7th century ad, but astronomy in Japan did not evolve straightforward in that century. There are thirty-one records that exist from that time, including four records on the Moon and planets. Correspondingly, a new interpretation of Japanese ancient history has been proposed. For the 8th, 9th, and 10th centuries, records have been compiled on the relative motion of the Moon and the planets, the motion of planets in the constellations, and stars seen in the daytime, as stated in Japanese recorded history. These records are written in Chinese, as in the case of the Nihongi, but have been translated into English. The orbits of the Moon and planets have been calculated using the NASA Jet Propulsion Laboratory (JPL) development ephemeris (DE) in order to confirm the validity of the records. The numbers of records and observations are not the same because one record may contain multiple observations. The accuracy of individual observations is discussed.
Space Resource Utilization
Throughout human history, resources have been the driving force behind the exploration and settling of our planet and also the means to do so. Similarly, resources beyond Earth will make space the next destination in the quest for further exploration and economic expansion of our species. The multitude of celestial bodies surrounding Earth and the space between them hold a vast wealth of resources for a variety of applications. The unlimited solar energy, vacuum, radiation, and low gravity in space, as well as the minerals, metals, water, atmospheric gases, and volatile elements on the Moon, asteroids, comets, and the inner and outer planets of the Solar System and their moons, constitute potential valuable resources for robotic and human space missions and for future use on our own planet. In the short term, these resources could be transformed into useful materials at the site where they are found to extend mission duration and to reduce the costly dependence on materials sent from Earth. Making propellants and human consumables from local resources can significantly reduce mission mass, cost, and risk, enabling longer stays and fueling transportation systems for use within and beyond the planetary surface. Use of finely grained surficial dust and rocks can serve for habitat and infrastructure construction, radiation protection, manufacturing parts, and growing crops. In the long term, material resources and solar energy could also be brought to Earth if obtaining these resources and meeting energy demands locally prove to be no longer economically or environmentally acceptable. However, just like on Earth, not all challenges to identify, extract, and utilize space resources are scientific and technological. As nations and private companies start working toward extracting extraterrestrial resources, an international legal framework and sound socioeconomic policies need to be put in place to ensure that these resources are used for the benefit of all humanity. Space resources promise to unleash an unprecedented wave of exploration and of economic prosperity by utilizing the full potential and value of space. As we embark on this new activity, it will be up to us, humans on planet Earth, to find the best alternatives to use resources beyond our planet effectively, responsibly, and sustainably to make this promise a reality.
Sun, Moon and Planets in Medieval European Folk Tradition
The subject of astronomy in folk tradition, or folk astronomy, requires some explication. It is, for instance, not the same as ethnoastronomy, which primarily studies the astronomical ideas of contemporary societies. However, the subject overlaps with archaeoastronomy when defined widely as the interdisciplinary study of prehistoric, ancient, and traditional astronomies worldwide within their cultural context that includes both written and archaeological records. The most useful definition of “astronomy in folk tradition” might be “astronomy of the people or of the common man,” or even “lay astronomy,” left to us through tradition, where the term “astronomy” may, for further clarity, be replaced by “ideas and observations of the sky.” In any case, it is worth keeping in mind that the content of folk astronomy of one society may overlap with the content of established astronomy of another society at another time and place. Scientific ideas or theories have their roots in the past, even before the advent of any “experts.” Folk astronomy of the past is often less accessible for historical studies than mainstream astronomy, especially in a society leaving few records or artifacts. Revealing sources may, however, be found by looking beyond the conventional. For instance, various sources on mythology and religion may give information on the astronomical and cosmological ideas of previous societies. Purportedly fictional literature, like the works of Dante and Chaucer, may also yield information of this kind, although they were not explicitly composed for that purpose. But there are also writers who have deliberately written on the astronomical ideas of their society at their time, although their works were outside of the best known corpus and sometimes intended for common people. Two Old Norse examples are the 13th-century Norwegian King’s Mirror and the Icelandic 12th- to 14th-century material edited in the volume of Alfræði íslenzk II. Among other things, these sources treat phenomena that are not observable outside the subarctic region. A third example is the 14th–15th century North European Seebuch with practical information for seamen, partly linked to astronomy. In any case, two types of folk astronomy can be distinguished: (a) practical astronomy that people use as a tool in daily life, for example, to determine the time of day or year, or for travel and navigation; (b) ideas related to cosmology or cosmogony, religion, or supernatural beliefs, which would neither imply practical uses nor consequences.
The Moon and the Planets in Classical Greece and Rome
While the moon naturally featured in Mediterranean cultures from time immemorial, principally noted in the earliest literature as a marker of time, time-dependent constructs such as the calendar, and time-related activities, awareness and recognition of the five visible planets came relatively late to the Greeks and thence to the Romans. The moon underlies the local calendars of the Greeks, with documentary and literary evidence from the Late Bronze Age through the Imperial Roman period, and there are signs that the earliest Roman calendar also paid homage to the moon in its divisions of the month. However, although Homer in the 8th century BCE knows of a Morning and an Evening Star, he shows no indication of realizing that these are one and the same, the planet Venus. That particular identification may have come in the 6th century BCE, and it appears to have been not until the 4th century BCE that the Greeks recognized the other four planets visible to the naked eye—Saturn, Jupiter, Mars, and Mercury. This awareness probably came via contact with Babylonian astronomy and astrology, where identification and observations of the planets had figured from the 2nd millennium BCE and served as a basis for astrological prognostications. But it is time, not astrology, that lies at the heart of Greek and Roman concerns with the moon and the planets. Indeed, the need to tell time accurately has been regarded as the fundamental motivation of Greek astronomy. A major cultural issue that long engaged the Greeks was how to synchronize the incommensurate cycles of the moon and the sun for calendrical purposes. Given the apparent irregularities of their cycles, the planets might seem to offer no obvious help with regard to time measurement. Nonetheless they were included by Plato in the 4th century BCE in his cosmology, along with the sun and moon, as heavenly bodies created specifically to compute time. Astrology then provided a useful framework in which the sun, moon, planets, and stars all combined to enable the interpretation and forecasting of life events. It became necessary for the Greeks, and their successors the Romans, to be able to calculate as accurately as possible the positions of the heavenly bodies in order to determine readings of the past, present, and future. Greek astronomy had always had a speculative aspect, as philosophers strove to make sense of the visible cosmos. A deep-seated assumption held by Greek astronomers, that the heavenly bodies moved in uniform, circular orbits, lead to a desire over the centuries to account for or explain away the observed irregularities of planetary motions with their stations and retrogradations. This intention “to save the phenomena,”— that is, to preserve the fundamental circularity—was said to have originated with Plato. While arithmetical schemes had sufficed in Babylonia for such calculation, it was a Greek innovation to devise increasingly complex geometric theories of circular motions (eccentrics and epicycles) in an effort to understand how the sun, moon, and planets moved, so as to place them more precisely in time and space.
The Moon in Meso-America
What is known about the Moon among the ancient Maya of southern Mexico and Guatemala and the Nahuatl-speaking people of central Mexico, especially the Aztecs who lived in the Valley of Mexico and their neighbors in Puebla-Tlaxcala Valley, has been obtained from records related to astronomy and lunar cycles inscribed on Classic Maya monuments dating between ad 250 and 850/900. Modern scholarship focusing on the mathematical units and glyphic writing has helped in deciphering the records. Postclassic Maya codices dating from 1300 to 1500, sent to Europe shortly after the Spanish conquest, also have lunar tables that have been decoded by study of the lunar cycles and glyphs. Painted books dating prior to the conquest in 1521 are also known from central Mexico, but these can only be understood with the help of books that were painted by native artists later in the 16th century and annotated with texts written in Spanish and Nahuatl. These glosses provide information about lunar deities and beliefs about the Moon. Furthermore, knowledge of the Moon in Meso-America is greatly enhanced by ethnographic studies and study of iconographic representations of deities representing different lunar roles and phases.