The Questions That Astronomy Asks

As a discipline, astronomy does not impact society in the obvious ways that chemistry (pharmaceuticals), biology (ethics of genetic engineering), or computer science (the Internet) do. Yet astronomy is one of humanity's oldest scientific disciplines. Some of the earliestwrit-ten records are the writings of Babylonian astronomer-priests recording the motions of the planets with respect to the background stars. These early efforts were made by societies that did not have large amounts of leisure time, so clearly there must have been some social usefulness to such astronomical observations. In what ways was astronomy useful to society in those ancient times, say, in Babylon, circa 1000 b.c.e.? One obvious answer is that the heavens were remarkably good keepers of time, and they reflected the seasonal cycles that were of the utmost importance to agricultural societies. Much as the U.S. Naval Observatory keeps the official time for the nation today, synchronizing the Internet, business transactions, and some other aspects of day-to-day life, so too did ancient astronomer-priests keep time for their societies, predicting seasonal change, establishing festival dates, and advising leaders of auspicious times to begin military campaigns.

Archaeoastronomy is the study of the astronomical efforts of ancient peoples as evidenced by alignments at archaeological sites and anthropological studies of the people who lived at or near such sites. This endeavor has shown us that early societies were clearly aware of events like the summer and winter solstices, fall and spring equinoxes, and the cyclical motions of the planets and the moon. For both practical and ceremonial reasons, this form of timekeeping was important. One practical reason was to know when during the year to plant and harvest crops. The ceremonial reasons may have been to anticipate (as is clear from some archaeological sites) and celebrate such events as the end of the sun's dipping low in the sky and the start of its ascent to its greatest height in late June at the summer solstice.

Alignments of stones from Europe to the Americas show clearly that societies kept track and cared about the positions and motions of the sun. It would have been easy for a careful observer to note, for example, that in the course of a year the sun sets farther and farther to the south each day as the winter months approach. It then appears to stand still on the winter solstice and move to the north each day until about June 21, when it stands still and begins its motion to the south once again.

The first day of each lunar month was fixed by the first observation of the new moon. It is possible that the regular observation of the bright moon and its phases—which fixed months for purposes of business and government—led to early astronomers noticing other regular motions. The Sumerians invented cuneiform script, and some of the earliest written records of astronomy are found in this form. Texts survive from the time of the first Babylonian dynasty (c. 2000 B.C.E.) recording the positions of the sun and moon, names of constellations, and the position of the planet Venus with respect to the stars. Observations like these made by early societies and the pseudoscientific inferences derived from them are the origin of astrology. While most people today dismiss astrology as mere superstition, the presence of horoscopes in daily newspapers attests to the fact that many of us still find comfort in the fantasy that the future can be predicted by the configuration of the heavens. In fact, one might argue that astrology impacts the daily life of more people on the Earth than astronomy.

The keeping of the calendar by means of astronomical observations was clearly of use to early societies. By about 1000 b.c.e., astronomical observations reveal a deeper concern with astrology, interpreting the positions of the planets and stars to predict the future. By this time, astronomers had clearly noticed the relative movements of the moon, stars, and bright planets, and they were chronicling them. There is also evidence that, by about 800 b.c.e., astrologers had noticed the regularity of lunar eclipses and were able to predict them. Late Babylonian texts further indicate an ability to predict solar eclipses, which means that astronomers were accumulating data over periods of many years and looking for patterns in the data. While many of the conclusions that these ancient observers drew were astrological, their observations and techniques were often the products of sound scientific method. By 1000 b.c.e., Chinese astronomers were keeping careful records of the daily motion of the stars and such transient phenomena as comets.

Until the advent of the Greek philosophers, all astronomical efforts that we know about were confined to a priestly class. As J.L.E. Dreyer comments, "[Speculations on the origin and construction of the world were always interwoven with mythological fancies to the exclusion of independent thought. Astronomy may be said to have sprung from Babylon, but cosmology . . . dates only from Greece." Trade and conquest at the time ofAlexander brought the Greek people into contact with those farther to the east, where astronomy and astrology had developed greatly in the previous two millennia. Greek astronomers began to move beyond record keeping and soothsaying to taking a measure of the world around them. Thales of Miletus (624-547 b.c.e.) apparently predicted a solar eclipse in 584 b.c.e. The Greek astronomer Aristarchus (310-230 B.c.E.)first suggested that the Earth was not at the center of the universe but that it orbited the sun and rotated on its axis. The daily motion of the sun and stars, then, were the result of the Earth's motion through space. So out of keeping with everyday experience was this suggestion, however, that it was not until the time of Nicolaus Copernicus (1473-1543), 1,700 years later, that the heliocentric idea became widely accepted. The writings of Copernicus began a revolution in our concept of where we fit into the universe, which proceeded through the work of Johannes Kepler (15711630), Galileo Galilei (1564-1642), and finally Isaac Newton (16421727). Newton's conception of the mechanics of the universe remained basically unchallenged until the twentieth century.

Greek astronomers were apparently the first people to have suggested that the Earth was not flat, as it appears to be on local scales, but spherical. The astronomer Eratosthenes (c. 250 b.c.e.) performed a simple but ingenious experiment, which not only showed that the surface of the Earth is curved but also yielded an accurate measurement of its circumference. When Eratosthenes made his estimate of the size of the Earth, he placed humans on the surface of a very large sphere, around which (apparently) the entire universe revolved. Suddenly, the world over which humans had dominion was a much larger place, its local flatness an illusion caused by our tiny size. Were we large enough, the curvature of the Earth would have been obvious all along. It is not clear, though, that Eratosthenes's conclusions reached a wide audience. In fact, we only know of his work because of references in later scientific and philosophical texts.

Early societies were surely more concerned with when to plant the crops than with the observation that the Earth was an enormous sphere. Much of the knowledge of the natural world put forth by

Greek astronomers and mathematicians was set aside until it was rediscovered in Europe during the Renaissance.

We know far more about the personalities of more recent astronomers and scientists than we do about their ancient counterparts. Isaac Newton, for example, was notoriously antisocial, and many great astronomers through time seem to have had little patience for the societies in which they lived. Astronomers tend to keep strange hours, staying up all night either to make their observations (at least, such is the case with optical astronomers) or to make sense of their data. Yet it is impossible to ignore that, since the earliest historical times, in addition to keeping the calendar, reading the future, and measuring the extent of the world we inhabit and of the universe, astronomers have been looking for answers to some of the most fundamental questions that humans ask. And recently, astronomers have been rather successful at finding observationally based answers to many of these questions. Some of the fundamental questions that face science and society today may eventually be answered by observations yet to be made by astronomers in coming centuries.

What are some of the questions, how have astronomers addressed them, and how might they continue to approach them in the future?

Why are we here and how did we get here? One might argue that some of the first people to make systematic observations of the night sky and record them, the astrologers, were looking for answers to this question. The question of the purpose of existence is perhaps as old as the consciousness of existence itself. While there are many levels to this question, astronomy has laid out a fairly detailed explanation of why we are here or, perhaps more accurately, how we got here. In the fullest sense, the question of why may not be a question for astronomers at all but for theologians and philosophers.

How long have we got? It is only natural to wonder how long we as a species will survive, and predictions that the world is coming to an end are surely older than astronomy. Astronomers have explored this question on many levels, from the lifetime of the Earth to that of the sun and even the lifetime of the universe. Astronomers are also deeply involved in the ongoing effort to track the orbits of potentially dangerous asteroids.

Are we unique? The Chinese have long referred to their land as the Middle Kingdom, and it is understandable that we all tend to think of our own location as the center of it all. Some of the most dramatic shifts in our understanding of exactly where we are located (in the solar system, in the galaxy, in the universe) have come about as a result of careful observations by astronomers.

Are we alone? One of the most frequent connections between astronomy and society comes from this fundamental question. From the profound discoveries of planets orbiting other stars to the ludicrous tabloid headlines seen at the grocery store checkout line, this topic— more than any other—garners attention from people who, otherwise, would not give astronomy a second thought.

We now turn to each of these questions in more detail and explore the ways in which astronomy forges connections to society by addressing some of its most fundamental questions.

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