In their role as teachers of the word and will of God, prophets occasion-ally mention natural processes or phenomena. Often these references are clearly symbolic or figurative, as when the scriptures speak of “the four quarters of the earth” to mean throughout the whole world. A nicely poetic example, “the earth rolls upon her wings” (D&C 88:45) is evocative, but hardly the basis for a scientific expedition to find those wings. Yet the Prophet Joseph Smith produced a significant corpus of writings in which are found statements regarding celestial objects. As an astronomer, I am drawn to ask: Do those statements indicate a correct understanding of nature—perhaps even beyond the science of his day? This article discusses the historical and scientific background of one such statement in the Pearl of Great Price.
Whenever conversations among Mormons turn to astronomy, many think of the Book of Abraham in the Pearl of Great Price, with its fascinating figures and the discussion of governing stars, set times, and a hierarchy of motions. Although that intriguing book is a natural springboard for all sorts of inquiries about history, language, and astronomy, this article focuses on a different part of the Pearl of Great Price, the Book of Moses.
Consider a series of statements written in June 1830 by Joseph Smith as he relived a vision given to Moses and published as chapter 1 of the Book of Moses, a sort of preface to the Joseph Smith Translation of the book of Genesis. Halfway through the chapter, Moses in vision appealed to God as to why he had made “these things” (many lands). Moses stood in the presence of God, and he heard God speak of many worlds:
And worlds without number have I created; and I also created them for mine own purpose; and by the Son I created them, which is mine Only Begotten. And the first man of all men have I called Adam, which is many. . . . For behold, there are many worlds that have passed away by the word of my power. And there are many that now stand, and innumerable are they unto man; but all things are numbered unto me, for they are mine and I know them. And it came to pass that Moses spake unto the Lord, saying: Be merciful unto thy servant, O God, and tell me concerning this earth, and the inhabitants thereof, and also the heavens, and then thy servant will be content. And the Lord God spake unto Moses, saying: The heavens, they are many, and they cannot be numbered unto man; but they are numbered unto me, for they are mine. And as one earth shall pass away, and the heavens thereof even so shall another come; and there is no end to my works, neither to
my words. For behold, this is my work and my glory—to bring to pass the immortality and eternal life of man. (Moses 1:33–39)
Since verse 39 outlines the goals of God himself, it is a favorite of many Mormons. Beyond that verse, LDS Church leaders and scholars have traditionally focused their attention on that part of the Moses statement relating to “worlds without number” as expressing the Mormon view that there are many inhabited worlds out in space. This discussion has been comprehensively treated by Erich Robert Paul.An anthology of statements by LDS Church leaders on almost every verse in the Pearl of Great Price has been given by author H. Donl Peterson. Regarding the verses cited above, however, LDS Church leaders (some of those cited or mentioned include James E. Talmage, Marion G. Romney, Orson Pratt, Joseph Smith, Spencer W. Kimball, John A. Widtsoe, Bruce R. McConkie, Parley P. Pratt, Brigham Young, and Joseph Fielding Smith) generally emphasized the content of the scriptures and have focused on the central message that other worlds (stars and planets) were created by God to be inhabited by his children.
Although the possibility of life in other stellar systems is indeed a fascinating topic and has been discussed by several authors, my focus here is on the statement by Joseph Smith that “worlds” come into existence, live for a time, and pass away (or, at least, pass into a different state). How does this statement accord with the astronomical knowledge of Joseph Smith’s day? This article attempts to answer that question.
While one must be careful not to read too much into a short statement, Joseph Smith seems to be taking a grand view of the universe. Although the words “worlds,” “earths,” and “heavens” are used, it is difficult to read this passage as referring to anything but stars and their accompanying planets. At a time when many people assumed stars were unchanging and the frontier of astronomical knowledge involved only the study of stellar positions and motions and even the basic facts about energy were still uncertain, the Prophet Joseph Smith wrote as Church doctrine of “earths,” “heavens,” and “worlds” coming into existence and passing away. As described in detail later, this statement is arguably the single best evidence that Joseph Smith glimpsed ideas not then clearly understood in the scientific world.
The Heavens Do Not Change
From time immemorial, people imagined that a flat earth sat immovably at the center of creation, and a hemispherical vault arched overhead (fig. 2). Sun, moon, stars, and planets were lights attached to the dome or holes in the dome through which heavenly light shone. As there was no reason to challenge this view, it held sway for ages. Even when, a few centuries before Christ, Greek scholars came to recognize the spherical nature of the earth, it still sat comfortably at the center of the solar system for centuries.
Ancient sky watchers who mastered the movements of the stars and constellations came to be regarded as scholars, priests, or wise men. Planets (literally, “wanderers”), including the sun and moon, presented a sterner test since the planets move slowly among the stars, and fanciful stories grew up in every tribe and clan about them: they were gods, or the abodes of gods, or symbols of gods. In Europe, everyday observations reinforced the teachings of the Christian Church that the heavens were unchanging.To many people, the heavens were also God’s signboards, on which, through planetary movements and frightening comets, God sent messages (usually warnings) to mortals.
Scholars or priests among the Babylonians, Egyptians, and Chinese carefully recorded the appearance and movements of celestial objects. However, available documents indicate that the Greeks were the first to ponder the mechanisms behind the movements of the celestial bodies; in modern terminology, they were the first theoretical model builders. Some of their speculations were wildly incorrect, but they nevertheless took important steps forward. For example, Eratosthenes (ca. 276–ca. 195 BC) measured the size of the earth; several scholars, among them Heraclides of Pontus (ca. 390–ca. 339 BC), taught that the earth rotated on its axis (instead of the supposed daily rotation of the heavens as maintained by Plato and Aristotle); Aristarchus of Samos (ca. 310–230 BC) estimated the relative distances and sizes of the sun and moon and even dared to suggest the huge, bright sun was the center of the solar system; Hipparchus (ca. 190–ca. 120 BC) actually discovered the precession of the equinoxes (due to the wobble of the earth’s axis); and Ptolemy (ca. AD 90–ca. AD 168) famously attempted (in his Almagest) to account for the motions of the planets through a complicated system of spheres and epicycles (small spheres upon larger spheres).
Aristotle (384–322 BC) summarized Greek thought, and his teachings about nature and the universe held sway for eighteen centuries in Europe, where he was “The Philosopher.” Aristotle divided the world into “terrestrial” and “celestial” realms, the latter consisting of everything outside “the sphere of the moon,” that is, the hypothesized crystalline sphere that carried the moon in its orbit around the stationary earth. Everything on earth consisted of the four elements—earth, water, air, and fire—while heavenly things consisted of the fifth element, “quintessence.” Motion arose as elements sought their “natural” places. Comets (and even the sun), Aristotle taught, were terrestrial exhalations that ignited when they reached the celestial sphere.
The works of Aristotle were translated into Arabic and then re-entered Europe in the twelfth and thirteenth centuries, where they were amalgamated with Christian theology, most notably by Albertus Magnus (1193/1206–1280) and especially by his most famous student, St. Thomas Aquinas (1225–1274).The result, often called scholasticism, came to be accepted almost as scripture. As one source puts it: “It was no fault of the writer [Aristotle] that his books were accorded almost divine authority.” To oppose Aristotle was to oppose the Roman Catholic Church (as Bruno, with his infinite universe, and Galileo, with his telescopic observations, discovered), and the unchangeableness of celestial objects became an article of faith.
Although Christian theologians had long discussed the attributes of God, on one point most everyone agreed: God is changeless. If God is unchanging, his celestial creations must be unchanging as well. Objects on earth—stones, trees, and humans—naturally change, but heavenly things are as unchanging as is God. So runs the logic. Surely the moon, sun, and planets are unchangeable—they are the epitome of constancy.
The unchanging nature of heavenly bodies has probably remained the belief of most people from the dawn of human existence. Philosopher-mathematician René Descartes (1596–1650) presented this idea in its extreme form: the immutable nature of God requires that objects he created must also be immutable.Physicist Timothy Ferris adds, “If we were to express in a single word the principal liability of the prescientific philosophies of nature—if, to put it another way, we were to name the one among their shortcomings that science has done the most to repair—I think it would be that they presumed that the universe was static. Many thinkers dismissed change as an illusion.” Large fractions of the population throughout the world and especially in the United States cling to these medieval beliefs: that the earth and heavens were created in the last ten thousand years or so and things have remained more or less unchanged since then.
It may have been William Herschel (1738–1822) who first speculated about the birth of stars. Born in Germany, he became a musician, moved
to England to further his career, became interested in astronomy, learned to cast and polish metal mirrors, and constructed the largest and best telescopes then in the world. With the assistance of his remarkable sister, Caroline, Herschel systematically observed the sky, discovered the planet Uranus along with several comets, made the first attempt to measure the size and shape of the star system (our galaxy) and studied numerous hazy celestial clouds (nebulae). For the first time, Herschel was able to resolve some of these clouds into clusters of stars, and he at first assumed all were composed of stars. However, even with increasingly powerful telescopes, certain of these fuzzy clouds could not be resolved but remained “shining fluid.” Herschel speculated in 1811 and 1814 that “cloudy” stars might be an early stage of star formation, and these might later condense into stars or star clusters.
Other philosophers and scientists of that day may also have speculated about the lives of stars, but Joseph Smith differed by announcing the coming and going (formation and dying out) of stars as a matter of Church doctrine.
What Is a Star?
To untangle the complicated story of the birth, life, and death of a star and its planetary system, if any, required a good deal of scientific knowledge about the distance, size, mass, temperature, and chemical composition of a star, and that task required decades of effort on the part of many scientists. In 1830, when Joseph Smith wrote what has become chapter 1 in the Book of Moses, there was practically no scientific understanding of these quantities even for the sun, much less the stars.
If the earth moves in an orbit around the sun, its motion must be reflected in a similar slight movement of nearby stars against the distant starry background. Such tiny changes were sought in vain by Galileo (1564–1642), who was therefore unable to answer satisfactorily his critics who maintained the earth was stationary. Finally, in 1838, the German astronomer F. W. Bessel (1784–1846)was able to measure the apparent movement (called the parallax) of a faint star in the constellation Cygnus. Combining the parallax with the known size of earth’s orbit immediately gave the distance to the star. Determination of the distance to other nearby stars continues to the present, for only when the distance is known can absolute quantities such as mass, size, and power output be determined.
On the theoretical side, Immanuel Kant (1724–1804) had proposed in 1755 that the solar system originated from a huge gaseous cloud that flattened as it rotated and contracted under natural forces to produce the solar system, and Pierre-Simon de Laplace (1749–1827) made the first dynamical calculation of such a process. Although based on simplified models, these were the first scientific attempts to explain the origin and evolution of the solar system.
Two intertwined problems then stood in the way of further scientific progress on the nature of stars and their life cycles: (1) to discover a star’s energy stores and (2) to infer the life story (evolution) of a star. These in turn required (a) an understanding of the nature of energy and its relation to work and heat, (b) a fair estimate of the total power output of the sun and stars, and (c) knowledge of the chemical composition of the stars. These endeavors required decades of research. An understanding of the relations between electrical energy, heat, and mechanical work developed slowly through the period of 1820 to 1850; solar radiation was first measured roughly by 1837 but much more accurately by 1900;and the chemical composition of the sun was discovered through spectroscopy during the period 1860 to 1920. Not until 1869 did the Russian chemist Dmitri Mendelayev (1834–1907) publish the periodic table of the chemical elements, but even that was incomplete. For example, the element helium—crucial for stellar energy production—was first detected in spectral lines of an eclipsed sun in 1868 and was finally found on earth in 1895.
It is easy to overlook the fact that astrophysics is a new science, the birth of which is often dated from the advent of quantitative spectroscopy in the early 1900s.
Source of the Sun’s Energy
In the century following Newton, a few thinkers wondered whether the energy of the sun might need replenishment from time to time.If so, one first thought of combustion or other chemical reactions, but this source was shown to be insufficient by the German physician and physicist Julius Robert Mayer (1814–1878), who agreed with others that comets (whose mass was then unknown) and meteorites striking the sun could supply the needed energy.
One science historian divides considerations of the sources of stellar energy after Newton into four periods: (1) from Newton to about the middle of the 1800s, during which time a few thinkers wondered about possible sources for replenishing the sun’s energy, should they be needed; (2) an understanding of energy and the conservation of energy, put forward in the 1840s and 1850s by Julius Robert Mayer, James Prescott Joule (1818–1889), John James Waterston (1811–1883), William Thomson (also known as Lord Kelvin, 1824–1907), Ludwig Boltzmann (1844–1906), and others,who investigated quantitatively the energy stores of the sun for the first time; (3) the discovery of radioactivity in the late 1890s, which presented a possible new (nuclear) energy source—this stage reached its culmination with the discovery by Hans Bethe (1906–2005) in the 1930s of an actual nuclear pathway that produced energy from the conversion of hydrogen to helium (now called the CNO cycle); and (4) the modern synthesis, since about 1950, which depends on much more knowledge of nuclear reaction rates, more complete observations, and very fast computers.
In 1854, the German physicist Hermann von Helmholtz (1821–1894) proposed a new theory for the sun’s energy stores: gravitational contraction of the sun would supply the required energy for a few tens of millions of years,and this erroneous suggestion was widely accepted as the solution to the solar energy problem. For example, a popular American astronomy book of 1902 (revised in 1910) states: “One of the most interesting and important problems of modern science relates to the explanation of the method by which the sun’s heat is maintained. . . . Positively, the solar radiation can be accounted for on the hypothesis, proposed first by Helmholtz, that the sun is shrinking slowly but continuously.” As time passed, however, discoveries by geologists, biologists, and physicists demanded a much greater age for the solar system than could be supplied by gravitational contraction.
After Einstein’s theory of relativity showed that matter and energy were two sides of the same coin, it was suggested that matter annihilation might maintain the solar energy. Also, several physicists in the early 1900s proposed the fusion of hydrogen to helium as the source of stellar energy, and fierce debate ensued between the partisans of annihilation and those of fusion. Contributions to the solution of the problem came from several scientists and was finally settled in the 1930s when the German-American physicist Hans Bethe found a viable pathway for the fusion of hydrogen to helium in stellar interiors (which garnered him a Nobel Prize).
The other half of the story is the evolution of stars. It is even more fascinating, but the modern understanding of stellar evolution has developed almost entirely since 1900 and therefore long after the time of interest for our study of the statements of Joseph Smith.
In the early 1900s, two astronomers (Ejnar Hertzsprung from Denmark and Henry Norris Russell from America) independently plotted color and luminosity for a few dozen stars and found they fell into two groups—a large group now called the main sequence and a smaller group now called the red giants (fig. 4). The main sequence includes stars that cover the full range of absolute magnitude (a measure of brightness), but the red-giant stars are all red and bright. It was impossible to resist the notion that the largest group (the main sequence) was an evolutionary sequence, and that erroneous idea dominated the field of astrophysics for several decades. Gradually, however, astrophysicists realized that stars on the main sequence differed in mass, and mass determined a star’s entire evolutionary history. Stellar birth, evolution, and death are now well understood, especially so because detailed theoretical and observational studies have proceeded hand in glove for decades.
Here’s the rest of the story. For convenience, let’s divide the life of a star such as the sun into four stages:
1. As gigantic clouds of gas and dust particles in the Milky Way Galaxy swirl around and collide under the action of fierce winds and ultraviolet radiation from supernovas, red giants, and young massive stars, they expand, collapse, or fragment. On occasion the resulting cloudlets become self-gravitating so that they maintain their integrity. Gravitation then quickly compresses the cloud until the outward pressure of hot gas and radiation generated by the compression and subsequent nuclear reactions balances the inward gravitational force. At that point, a star is born. Stars generally form in groups, and clouds illuminated by young, hot stars (stellar nurseries) form many of the breathtaking photographs from the Hubble and Spitzer space telescopes (figs. 1, 3, and back cover).
2. A star spends most of its life (neglecting its long end state) as a stable gaseous globe that burns hydrogen in its core—a phase astronomers call the main sequence. This is the current stage of the sun. (Scientists use the phrase “hydrogen burning” to refer to nuclear fusion; that is, the fusing of four hydrogen atoms to one helium atom with the emission of a great deal of energy.) Our sun has enough hydrogen fuel in its core to maintain its current energy output for 10 to 11 billion years, about 4.6 billion years of which have already passed.
Stars with a mass greater than that of the sun burn their nuclear fuel so much more vigorously that their main-sequence lifetimes are correspondingly shorter. Many generations of high-mass stars have therefore already come and gone. On the other hand, all stars ever formed with masses less than about one-tenth of a solar mass are still shining dimly in our skies.
3. When core hydrogen has been fused into helium, hydrogen burning takes place only in a shell around the core. Because there is no longer an outward force in the core to balance gravity, the core contracts and the energy liberated is deposited in the envelope, which swells and cools to create a red-giant star. In the red-giant stage, stars such as the sun can also burn helium to carbon and oxygen, but these fuels burn rapidly, and the red-giant stage lasts only a few hundred million years. Finally, as the star swells to an enormous size (for example, the sun will become as big as earth’s orbit), convection dredges up to the surface part of the material that has been processed by nuclear reactions. Toward the end of the red-giant stage, the star throws off its outer layer, revealing an intensely hot inner core, called a white-dwarf star.
4. A star’s life is governed by its mass, and mass difference is striking in the “end game.” Stars with masses similar to the sun go through the stages outlined above, throw off their envelope, and leave behind hot, compact cores. Having no burnable nuclear fuel, these white dwarfs slowly radiate away their thermal energy and gradually cool down. More massive stars are able to burn heavier fuels (heavier atoms); however, no energy can be extracted from iron by nuclear burning. A star more massive than about eight solar masses burns fuel up to iron and explodes as a supernova (fig. 6). It crushes its extremely compact core into a pile of neutrons—a neutron star. Even more massive stars (greater than fifteen to twenty solar masses) explode as supernovas and leave as a remnant a black hole.
How trustworthy are the evolutionary scenarios sketched above? Theory and observation complement each other beautifully in the endeavor to understand the birth and life story of a star. Many stars in all stages of evolution have been examined, and these are always available for inspection by everyone. For example, newly formed (pre-main-sequence) stars, stable main-sequence stars (in the same phase as our sun) of all masses, red-giant stars, post-red-giant stars that have just thrown off their envelopes to reveal the white dwarf star underneath, binary stars, and even exploding stars have been carefully observed with a variety of instruments. Examples even of such short-lived phenomena as supernovae have been observed, and their remnants are scattered over the sky. Careful observations of the sun at all wavelengths, methodical observations of stars of different masses, systematic observations of star clusters (where all stars are formed of about the same material at about the same time), and detailed observations of binary stars are all used to check the extensive calculations of stellar models with different masses, temperatures, and chemical compositions.
Beyond their fascinating life story, stars are valuable for another reason: they are atom factories. Hydrogen, helium, and a bit of lithium were created in the Big Bang, but heavier elements such as carbon, nitrogen, oxygen, silicon, iron, and all the rest were created from hydrogen and helium deep inside stars. Astronomers are fond of pointing out that, outside the tiny amounts of the three elements created in the Big Bang, everything on or in the earth, and even our own bodies, is made of stardust.
Do planets circle these stars? Are they inhabited? If so, what will happen to them? Systematic searches for planets around stars outside our solar system represent a relatively new field of astronomy, but more than five hundred exoplanets (planets outside the solar system) have already been confirmed.Until 2010, only large, Jupiter-like planets had been found, and these tend to be in eccentric orbits and to pass surprisingly close to their stars. Then, in September 2010, astronomers in the Lick-Carnegie Exoplanet Survey announced that they had detected an earthlike planet in the Gliese 581 planetary system. They estimated this planet’s mass to be “three to four times that of earth.” This discovery is as yet unconfirmed, and another group of astronomers has questioned the discovery. But five months after this announcement, on February 2, 2011, NASA’s Jet Propulsion Laboratory in Pasadena, California, announced that NASA’s Kepler mission has discovered several hundred new planet candidates, bringing the total planet candidates Kepler has found up to 1,235. Of these, sixty-eight are approximately the size of earth, and fifty-four lie in a habitable zone (neither too near to nor too far from their stars). Again, these discovered planet candidates are not yet confirmed (this process should take another three years), but all were found in Kepler’s field of view, which covers only one four-hundredth of the sky. “In one generation,” said NASA Administrator Charles Bolden, “we have gone from extraterrestrial planets being a mainstay of science fiction, to the present, where Kepler has helped turn science fiction into today’s reality.” Undoubtedly, as better instruments are built, more and smaller planets will be found. Yes, as the scriptures cited above indicate, in our galaxy alone there are stars without number and likely planets without number. However, in spite of intensive searches with ever-increasing sensitivity, no signal of any kind has yet been detected from any intelligent civilization.
Astronomy in America
What was the state of affairs in American astronomy in 1830? The Louisiana Purchase had been made in 1803, Meriwether Lewis and George Rogers Clark had made their famous wilderness journey to the Pacific coast from 1804 to 1806, and the War of 1812 was still a vivid memory. Astronomy was almost unknown in pioneer America.
Lectures in astronomy (then generally considered a subfield of mathematics because it dealt almost exclusively with the motions of the planets and stars) had been given at Harvard College since its founding in 1642,but much of the college was destroyed by a fire in a fierce snowstorm in January 1764. Although the idea of an observatory, to be the first observatory in America, was certainly discussed, lack of interest and money prevented any concrete action. Later, the matter was taken up again, and Harvard College Observatory was established in 1839. It was not until 1847, however, that their hoped-for fine telescope arrived—a refractor with a lens fifteen inches in diameter—the largest in America and perhaps in the world.
Meanwhile, other astronomical observatories were being built in several eastern states, though telescopes often came later. The first observatory building was constructed at the University of North Carolina in 1831. Other early observatories, with their dates of completion, were: Yale in 1831, Williams College in 1836, West Point in 1839, Philadelphia High School (yes, a high school) in 1840, and the public observatory in Cincinnati in 1845. Other early observatories were established in Tuscaloosa, Alabama, in 1843; Georgetown, 1843; Amherst, 1847; and Shelby College, 1847.Not a single observatory existed in America at the time Joseph Smith made his statement regarding the birth and death of stars.
In this article, we have examined the state of knowledge of stars and stellar evolution in 1830 when Joseph Smith wrote that old stars or worlds “pass away” and new stars are formed or “come” into being.This idea is arguably one of the most prescient contributions of the Pearl of Great Price and of Joseph Smith. It contains a clear hint of stellar birth and death that appears to be ahead of common knowledge and even scientific knowledge of that time. Modern understanding of stellar evolution rests firmly upon a foundation of observational facts and a well-developed theoretical understanding, naturally accepted by all scientists even while they continue to search for deeper understanding. The formation, life, and eventual end of stars are now well understood.
The life story of a star is a grand tale, very little of which was known at the time Joseph Smith made the statements that appear in the Book of Moses in the Pearl of Great Price.
About the Author
1. For a thorough discussion of the possibility of life on other worlds, see Erich Robert Paul, Science, Religion, and Mormon Cosmology (Urbana, Ill.: University of Illinois Press, 1992).
2. H. Donl Peterson, The Pearl of Great Price: A History and Commentary (Salt Lake City: Deseret Book, 1987), 102–8; of similar effect, see Jeffrey M. Bradshaw, In God’s Image and Likeness: Ancient and Modern Perspectives on the Book of Mormon (Salt Lake City: Eborn, 2010), 65–68.
3. David Millar, Ian Millar, John Millar, and Margaret Millar, The Cambridge Dictionary of Scientists, 2d ed. (Cambridge, UK: Cambridge University Press, 2002), 11.
4. Sara J. Schechner, Comets, Popular Culture, and the Birth of Modern Cosmology (Princeton, N.J.: Princeton University Press, 1997), 50.
5. Michael Hoskin, ed., The Cambridge Concise History of Astronomy (Cambridge, UK: Cambridge University Press, 1999), 26, 33–34, 38–40.
6. Hoskin, Cambridge Concise History of Astronomy, 75.
7. Millar, Cambridge Dictionary of Scientists, 11.
8. John Hedley Brooke, Science and Religion: Some Historical Perspectives (Cambridge, UK: Cambridge University Press, 1991), 75; Hoskin, Cambridge Concise History of Astronomy, 119, 122.
9. Timothy Ferris, The Whole Shebang: A State-of-the-Universe(s) Report (New York: Simon Touchstone, 1997), 170.
10. Herschel’s original paper is reprinted in Marcia Bartusiak, Archives of the Universe: 100 Discoveries That Transformed Our Understanding of the Cosmos (New York: Vintage Books, 2004), 130–31.
11. Arthur Berry, A Short History of Astronomy (New York: Charles Scribner’s Sons, 1899), 323–24, 340, 420.
12. Charles Singer, A Short History of Scientific Ideas to 1900 (Oxford: Oxford University Press, 1959), 248 n. 1; 313; Millar, Cambridge Dictionary of Scientists, 36.
13. Berry, Short History of Astronomy, 397.
14. Millar, Cambridge Dictionary of Scientists, 248.
15. Singer, Short History of Scientific Ideas, 442–43.
16. Karl Hufbauer, “Stellar Energy Problem,” in History of Astronomy: An Encyclopedia, ed. John Lankford (New York: Garland Publishing, 1997), 490–93.
17. David Dewhirst and Michael Hoskin, “The Message of Starlight: The Rise of Astrophysics,” in Hoskin, Cambridge Concise History of Astronomy, 234.
18. See, for example, David Lindley, Degrees Kelvin: A Tale of Genius, Invention, and Tragedy (Washington, D.C.: Joseph Henry Press, 2004), 260–308.
19. Hoskin, Cambridge Concise History of Astronomy, 266–67.
20. Hermann von Helmholtz, “On the Source of the Sun’s Heat,” adapted from “On the Origin of the Planetary System,” in Popular Scientific Lectures, vol. 2 (1908), as quoted in Harlow Shapley and Helen E. Howarth, A Source Book on Astronomy (New York: McGraw-Hill, 1929), 311–15.
21. Charles A. Young, Manual of Astronomy: A Text-Book (Boston: Ginn and Co., 1902), 254.
22. The count by the Jet Propulsion Laboratory at the California Institute of Technology, online at http://planetquest.jpl.nasa.gov/atlas/atlas_index.cfm, was 528 on February 25, 2011.
23. “NASA and NSF-Funded Research Finds First Potentially Habitable Exoplanet,” NASA, http://www.nasa.gov/topics/universe/features/gliese_581_feature.html.
24. See Leslie Mullen, “Doubt Cast on Existence of Possibly Habitable Alien Planet,” October 12, 2010, available at http://www.msnbc.msn.com/id/39640401/ns/technology_and_science-space.
25. “Earth-Size Planet Candidates Found in Habitable Zone,” NASA, Jet Propulsion Laboratory, February 2, 2011, http://www.jpl.nasa.gov/news/news.cfm?release=2011-036.
26. Bessie Zaban Jones and Lyle Gifford Boyd, The Harvard College Observatory: The First Four Directorships, 1839–1919 (Cambridge, Mass.: Harvard University Press, 1971), 1.
27. Jones and Boyd, Harvard College Observatory, 12, 42, 67–68.
28. Jones and Boyd, Harvard College Observatory, 36–38.
29. Thanks to Professor B. Kent Harrison, Brigham Young University, for helpful comments on the manuscript.