What do Virginia Woolf, the rotation of hurricanes, Babylonian kings and Einstein's General Theory Relativity all have in common? Eclipses. Always spectacular and, today, precisely predicable, eclipses have allowed us to know when the first Olympic games were played and, long before the first space probe, that the Moon was covered by dust. Eclipses have stunned, frightened, emboldened and mesmerized people for thousands of years. They were recorded on ancient turtle shells discovered in the Wastes of Yin in China, on clay tablets from Mesopotamia and on the Mayan "Dresden Codex." They are mentioned in Homer's Iliad and Odyssey and at least eight times in the Bible. Columbus used them to trick people, while Renaissance painter Taddeo Gaddi was blinded by one. Sorcery was banished within the Catholic Church after astrologers used an eclipse to predict a pope's death. In Mask of the Sun, acclaimed writer John Dvorak the importance of the number 177 and why the ancient Romans thought it was bad to have sexual intercourse during an eclipse (whereas other cultures thought it would be good luck). Even today, pregnant women in Mexico wear safety pins on their underwear during an eclipse. Eclipses are an amazing phenomena-unique to Earth-that have provided the key to much of what we now know and understand about the sun, our moon, gravity, and the workings of the universe. Both entertaining and authoritative, Mask of the Sun reveals the humanism behind the science of both lunar and solar eclipses. With insightful detail and vividly accessible prose, Dvorak provides explanations as to how and why eclipses occur-as well as insight into the forthcoming eclipse of 2017 that will be visible across North America.

Knowledge of the structure of the cosmos, Plato suggests, is important in organizing a human community which aims at happiness. This book investigates this theme in Plato's later works, the Timaeus, Statesman, and Laws. Dominic J. O'Meara proposes fresh readings of these texts, starting from the religious festivals and technical and artistic skills in the context of which Plato elaborates his cosmological and political theories, for example the Greek architect's use of models as applied by Plato in describing the making of the world. O'Meara gives an account of the model of which Plato's world is an image; of the mathematics used in producing the world; and of the relation between the cosmic model and the political science and legislation involved in designing a model state in the Laws. Non-specialist scholars and students will be able to access and profit from the book.

The quest to find a theory of quantum gravity that could potentially explain everything. Nearly 60 years ago, Nobel Prize-winners Arno Penzias and Robert Wilson stumbled across a mysterious hiss of faint radio static that was interfering with their observations. They had found the key to unravelling the story of the Big Bang and the origin of our universe. That signal was the Cosmic Microwave Background (CMB), the earliest light in the universe, released 379,000 years after the Big Bang. It contains secrets about what happened during the very first tiny increments of time, which had consequences that have rippled throughout cosmic history, leading to the universe of stars and galaxies that we live in today. This is the enthralling story of the quest to understand the CMB radiation and what it can tell us of the origins of time and space, from bubble universes to a cyclical cosmos - and possibly leading to the elusive theory of quantum gravity itself.

Relativistic hydrodynamics is a very successful theoretical framework to describe the dynamics of matter from scales as small as those of colliding elementary particles, up to the largest scales in the universe. This book provides an up-to-date, lively, and approachable introduction to the mathematical formalism, numerical techniques, and applications of relativistic hydrodynamics. The topic is typically covered either by very formal or by very phenomenological books, but is instead presented here in a form that will be appreciated both by students and researchers in the field. The topics covered in the book are the results of work carried out over the last 40 years, which can be found in rather technical research articles with dissimilar notations and styles. The book is not just a collection of scattered information, but a well-organized description of relativistic hydrodynamics, from the basic principles of statistical kinetic theory, down to the technical aspects of numerical methods devised for the solution of the equations, and over to the applications in modern physics and astrophysics. Numerous figures, diagrams, and a variety of exercises aid the material in the book. The most obvious applications of this work range from astrophysics (black holes, neutron stars, gamma-ray bursts, and active galaxies) to cosmology (early-universe hydrodynamics and phase transitions) and particle physics (heavy-ion collisions). It is often said that fluids are either seen as solutions of partial differential equations or as "wet". Fluids in this book are definitely wet, but the mathematical beauty of differential equations is not washed out.

This manual takes a look at what we know about the 'red planet' that has fascinated man for centuries, and presents the next major challenge in the exploration of our solar system. From early telescopic observations through the dawn of the space age, do today's quest for life on Mars, using orbiters, landers and rovers, following the discovery of water ice below the planet's surface, this book explains the history of man's study and analysis of the planet, and how modern-day science has furthered out understanding of Mars.

When on a summer evening, astrophysicist Hubert Reeves went for a walk with his granddaughter, he was immediately assaulted by her questions: 'How big is the Universe? How far are the stars? Are there other universes like ours?'. This little book is the result of their discussion - a very clear and fulfilling explanation on where we come from and our place in the Universe. Here is a perfect occasion for everybody, and not only children, to revise their conceptions about the cosmos.

Is our universe dying?
Could there be other universes?
In "Parallel Worlds," world-renowned physicist and bestselling author Michio Kaku"--an" author who "has a knack for bringing the most ethereal ideas down to earth" "(Wall Street Journal)--takes readers on a fascinating tour of cosmology, M-theory, and its implications for the fate of the universe.
In his first book of physics since "Hyperspace, Michio Kaku begins by describing the extraordinary advances that have transformed cosmology over the last century, and particularly over the last decade, forcing scientists around the world to rethink our understanding of the birth of the universe, and its ultimate fate. In Dr. Kaku's eyes, we are living in a golden age of physics, as new discoveries from the WMAP and COBE satellites and the Hubble space telescope have given us unprecedented pictures of our universe in its infancy.
As astronomers wade through the avalanche of data from the WMAP satellite, a new cosmological picture is emerging. So far, the leading theory about the birth of the universe is the "inflationary universe theory," a major refinement on the big bang theory. In this theory, our universe may be but one in a multiverse, floating like a bubble in an infinite sea of bubble universes, with new universes being created all the time. A parallel universe may well hover a mere millimeter from our own.
The very idea of parallel universes and the string theory that can explain their existence was once viewed with suspicion by scientists, seen as the province of mystics, charlatans, and cranks. But today, physicists overwhelmingly support string-theory, and its latest iteration, M-theory, as it is this onetheory that, if proven correct, would reconcile the four forces of the universe simply and elegantly, and answer the question "What happened before the big bang?"
Already, Kaku explains, the world's foremost physicists and astronomers are searching for ways to test the theory of the multiverse using highly sophisticated wave detectors, gravity lenses, satellites, and telescopes. The implications of M-theory are fascinating and endless. If parallel worlds do exist, Kaku speculates, in time, perhaps a trillion years or more from now, as appears likely, when our universe grows cold and dark in what scientists describe as a big freeze, advanced civilizations may well find a way to escape our universe in a kind of "inter-dimensional lifeboat."
An unforgettable journey into black holes and time machines, alternate universes, and multidimensional space, "Parallel Worlds gives us a compelling portrait of the revolution sweeping the world of cosmology.

A groundbreaking textbook on twenty-first-century general relativity and cosmology Kip Thorne and Roger Blandford's monumental Modern Classical Physics is now available in five stand-alone volumes that make ideal textbooks for individual graduate or advanced undergraduate courses on statistical physics; optics; elasticity and fluid dynamics; plasma physics; and relativity and cosmology. Each volume teaches the fundamental concepts, emphasizes modern, real-world applications, and gives students a physical and intuitive understanding of the subject. Relativity and Cosmology is an essential introduction to the subject, including remarkable recent advances. Written by award-winning physicists who have made fundamental contributions to the field and taught it for decades, the book differs from most others on the subject in important ways. It highlights recent transformations in our understanding of black holes, gravitational waves, and the cosmos; it emphasizes the physical interpretation of general relativity in terms of measurements made by observers; it explains the physics of the Riemann tensor in terms of tidal forces, differential frame dragging, and associated field lines; it presents an astrophysically oriented description of spinning black holes; it gives a detailed analysis of an incoming gravitational wave's interaction with a detector such as LIGO; and it provides a comprehensive, in-depth account of the universe's evolution, from its earliest moments to the present. While the book is designed to be used for a one-quarter or full-semester course, it goes deep enough to provide a foundation for understanding and participating in some areas of cutting-edge research. Includes many exercise problems Features color figures, suggestions for further reading, extensive cross-references, and a detailed index Optional "Track 2" sections make this an ideal book for a one-quarter or one-semester course An online illustration package is available to professors The five volumes, which are available individually as paperbacks and ebooks, are Statistical Physics; Optics; Elasticity and Fluid Dynamics; Plasma Physics; and Relativity and Cosmology.

Over the last forty years, scientists have uncovered evidence that if the Universe had been forged with even slightly different properties, life as we know it - and life as we can imagine it - would be impossible. Join us on a journey through how we understand the Universe, from its most basic particles and forces, to planets, stars and galaxies, and back through cosmic history to the birth of the cosmos. Conflicting notions about our place in the Universe are defined, defended and critiqued from scientific, philosophical and religious viewpoints. The authors' engaging and witty style addresses what fine-tuning might mean for the future of physics and the search for the ultimate laws of nature. Tackling difficult questions and providing thought-provoking answers, this volumes challenges us to consider our place in the cosmos, regardless of our initial convictions.

Not long ago, the Solar System was the only example of a planetary system - a star and the bodies orbiting it - that we knew. Now, we know thousands of planetary systems, and have even been able to observe planetary systems at the moment of their birth. This Very Short Introduction explores this new frontier, incorporating the latest research. The book takes the reader on a journey through the grand sweep of time, from the moment galaxies begin to form after the Big Bang to trillions of years in the future when the Universe will be a dilute soup of dim galaxies populated mostly by red dwarf stars. Throughout, Raymond T. Pierrehumbert introduces the latest insights gained from a new generation of telescopes that catch planetary systems at the moment of formation, and to the theoretical advances that attempt to make sense of these observations. He explains how the elements that make up life and the planets on which life can live are forged in the interiors of dying stars, and make their way into rocky planets. He also explores the vast array of newly discovered planets orbiting stars other than our own, and explains the factors that determine their climates. Finally, he reveals what determines how long planetary systems can live, and what happens in their end-times. Very Short Introductions: Brilliant, Sharp, Inspiring ABOUT THE SERIES: The Very Short Introductions series from Oxford University Press contains hundreds of titles in almost every subject area. These pocket-sized books are the perfect way to get ahead in a new subject quickly. Our expert authors combine facts, analysis, perspective, new ideas, and enthusiasm to make interesting and challenging topics highly readable.

Following on from a previous volume on Special Relativity, Andrew Steane's second volume on General Relativity and Cosmology is aimed at advanced undergraduate or graduate students undertaking a physics course, and encourages them to expand their knowledge of Special Relativity. Beginning with a survey of the main ideas, the textbook goes on to give the methodological foundations to enable a working understanding of astronomy and gravitational waves (linearized approximation, differential geometry, covariant differentiation, physics in curved spacetime). It covers the generic properties of horizons and black holes, including Hawking radiation, introduces the key concepts in cosmology and gives a grounding in classical field theory, including spinors and the Dirac equation, and a Lagrangian approach to General Relativity. The textbook is designed for self-study and is aimed throughout at clarity, physical insight, and simplicity, presenting explanations and derivations in full, and providing many explicit examples.

Here is the essential companion to Welcome to the Universe, a New York Times bestseller that was inspired by the enormously popular introductory astronomy course for non-science majors that Neil deGrasse Tyson, Michael A. Strauss, and J. Richard Gott taught together at Princeton. This problem book features more than one hundred problems and exercises used in the original course--ideal for anyone who wants to deepen their understanding of the original material and to learn to think like an astrophysicist. Whether you're a student or teacher, citizen scientist or science enthusiast, your guided tour of the cosmos just got even more hands-on with Welcome to the Universe: The Problem Book. * The essential companion book to the acclaimed bestseller* Features the problems used in the original introductory astronomy course for non-science majors at Princeton University* Organized according to the structure of Welcome to the Universe, empowering readers to explore real astrophysical problems that are conceptually introduced in each chapter* Problems are designed to stimulate physical insight into the frontier of astrophysics* Problems develop quantitative skills, yet use math no more advanced than high school algebra* Problems are often multipart, building critical thinking and quantitative skills and developing readers' insight into what astrophysicists do* Ideal for course use--either in tandem with Welcome to the Universe or as a supplement to courses using standard astronomy textbooks--or self-study* Tested in the classroom over numerous semesters for more than a decade* Prefaced with a review of relevant concepts and equations* Full solutions and explanations are provided, allowing students and other readers to check their own understanding

Tom Van Flandern's book adds a new dimension to cosmology--not only does it present a novel approach to timeless issues, it stands up to the closest scientific scrutiny. Even the most respected scientists today will readily admit that the Big Bang Theory is full of holes. But it takes a new look, like "Dark Matter, Missing Planets, and New Comets," to explain not only why the theory is wrong but what to substitute in its place. If you are curious about such things as the nature of matter and the origin of the solar system, but feel inadequately equipped to grasp what modern science has to say about such things, read this book. You will not get the all too common condescending attempt to water down the mysteries' of modern science into a form intelligible to little non scientist you, but rather a straightforward new theory, logically derived in front of your eyes, which challenges the roots of many of today's complex accepted paradigms, yet whose essence is simple enough to be thoroughly communicated to the intelligent layman without "losing it in the translation."

Biocentrism shocked the world with a radical rethinking of the nature of reality. But that was just the beginning. In Beyond Biocentrism, acclaimed biologist Robert Lanza, one of TIME Magazine's "100 Most Influential People in 2014," and leading astronomer Bob Berman, take the reader on an intellectual thrill-ride as they re-examine everything we thought we knew about life, death, the universe, and the nature of reality itself. The first step is acknowledging that our existing model of reality is looking increasingly creaky in the face of recent scientific discoveries. Science tells us with some precision that the universe is 26.8 percent dark matter, 68.3 percent dark energy, and only 4.9 percent ordinary matter, but must confess that it doesn't really know what dark matter is and knows even less about dark energy. Science is increasingly pointing toward an infinite universe but has no ability to explain what that really means. Concepts such as time, space, and even causality are increasingly being demonstrated as meaningless. All of science is based on information passing through our consciousness but science hasn't the foggiest idea what consciousness is, and it can't explain the linkage between subatomic states and observation by conscious observers. Science describes life as a random occurrence in a dead universe but has no real understanding of how life began or why the universe appears to be exquisitely designed for the emergence of life. The biocentrism theory isn't a rejection of science. Quite the opposite. Biocentrism challenges us to fully accept the implications of the latest scientific findings in fields ranging from plant biology and cosmology to quantum entanglement and consciousness. By listening to what the science is telling us, it becomes increasingly clear that life and consciousness are fundamental to any true understanding of the universe. This forces a fundamental rethinking of everything we thought we knew about life, death, and our place in the universe.

This text gives an introduction to particle physics at a level accessible to advanced undergraduate students. It is based on lectures given to 4th year physics students over a number of years, and reflects the feedback from the students. The aim is to explain the theoretical and experimental basis of the Standard Model (SM) of Particle Physics with the simplest mathematical treatment possible. All the experimental discoveries that led to the understanding of the SM relied on particle detectors and most of them required advanced particle accelerators. A unique feature of this book is that it gives a serious introduction to the fundamental accelerator and detector physics, which is currently only available in advanced graduate textbooks. The mathematical tools that are required such as group theory are covered in one chapter. A modern treatment of the Dirac equation is given in which the free particle Dirac equation is seen as being equivalent to the Lorentz transformation. The idea of generating the SM interactions from fundamental gauge symmetries is explained. The core of the book covers the SM. The tools developed are used to explain its theoretical basis and a clear discussion is given of the critical experimental evidence which underpins it. A thorough account is given of quark flavour and neutrino oscillations based on published experimental results, including some from running experiments. A simple introduction to the Higgs sector of the SM is given. This explains the key idea of how spontaneous symmetry breaking can generate particle masses without violating the underlying gauge symmetry. A key feature of this book is that it gives an accessible explanation of the discovery of the Higgs boson, including the advanced statistical techniques required. The final chapter gives an introduction to LHC physics beyond the standard model and the techniques used in searches for new physics. There is an outline of the shortcomings of the SM and a discussion of possible solutions and future experiments to resolve these outstanding questions. For updates, new results, useful links as well as corrections to errata in this book, please see the book website maintained by the authors: https://pplhcera.physics.ox.ac.uk/

The first volume of "Cosmos," his five-volume survey of the universe, appeared in 1845, though Humboldt had labored on the entire work for nearly half a century. He scrupulously sent sections of the work to other experts for suggestions and corrections. The last volume, put together from his notes after his death, appeared in 1861. The volumes were translated almost as rapidly as they appeared. This paperback edition reprints the Harper & Brothers edition, published in New York in 1858-59.

Demonstrating the unity of Tolkien's created world across Middle-earth's Ages. An in-depth examination of the role of divine beings in Tolkien's work, Tolkien's Cosmology: Divine Beings and Middle-earth brings together Tolkien's many references to such beings and analyzes their involvement within his created world. Unlike many other commentators, Sam McBride asserts that a careful reading of the whole of the author's corpus shows a coherent, if sometimes contradictory, divine presence in the world.In The Silmarillion, an epic history of the First Age of Middle-earth, Tolkien describes the Ainur, angelic beings under the direction of Eru Iluvatar, the legendarium's god, as creators of physical reality. Some of these divine beings, the Valar and the Maiar, enter physical reality to oversee its development and prepare for the appearance of sentient life forms in Middle-earth: Elves and Humans, Dwarves, and eventually Hobbits. In the early stages of this history, the Valar and Maiar interact directly with Elves and Humans, opposing the work of evil beings led by Melkor. Yet Tolkien appears, at first glance, to have ignored this pantheon in The Hobbit and The Lord of the Rings, set in the Third Age of Middle-earth. Tolkien's letters, however, suggest the cosmological structure continues. And representatives of the Valar and Maiar can be seen at work, such as Gandalf and Saruman. Tolkien also introduces hints that his divine beings continue to influence events invisibly, as with the prominence of luck in The Hobbit and fortuitous weather conditions in The Lord of the Rings. In the end, McBride argues, Tolkien's cosmology allows room for everything from poor decision-making to evil, suffering, and death, all part of a belief system that will make the final victory of Good much more powerful.

This advanced undergraduate text introduces Einstein's general theory of relativity. The topics covered include geometric formulation of special relativity, the principle of equivalence, Einstein's field equation and its spherical-symmetric solution, as well as cosmology. An emphasis is placed on physical examples and simple applications without the full tensor apparatus. It begins by examining the physics of the equivalence principle and looks at how it inspired Einstein's idea of curved spacetime as the gravitational field. At a more mathematically accessible level, it provides a metric description of a warped space, allowing the reader to study many interesting phenomena such as gravitational time dilation, GPS operation, light deflection, precession of Mercury's perihelion, and black holes. Numerous modern topics in cosmology are discussed from primordial inflation and cosmic microwave background to the dark energy that propels an accelerating universe. Building on Cheng's previous book, 'Relativity, Gravitation and Cosmology: A Basic Introduction', this text has been tailored to the advanced student. It concentrates on the core elements of the subject making it suitable for a one-semester course at the undergraduate level. It can also serve as an accessible introduction of general relativity and cosmology for those readers who want to study the subject on their own. The proper tensor formulation of Einstein's field equation is presented in an appendix chapter for those wishing to glimpse further at the mathematical details.

Heart of Darkness describes the incredible saga of humankind's quest to unravel the deepest secrets of the universe. Over the past thirty years, scientists have learned that two little-understood components--dark matter and dark energy--comprise most of the known cosmos, explain the growth of all cosmic structure, and hold the key to the universe's fate. The story of how evidence for the so-called "Lambda-Cold Dark Matter" model of cosmology has been gathered by generations of scientists throughout the world is told here by one of the pioneers of the field, Jeremiah Ostriker, and his coauthor Simon Mitton. From humankind's early attempts to comprehend Earth's place in the solar system, to astronomers' exploration of the Milky Way galaxy and the realm of the nebulae beyond, to the detection of the primordial fluctuations of energy from which all subsequent structure developed, this book explains the physics and the history of how the current model of our universe arose and has passed every test hurled at it by the skeptics. Throughout this rich story, an essential theme is emphasized: how three aspects of rational inquiry--the application of direct measurement and observation, the introduction of mathematical modeling, and the requirement that hypotheses should be testable and verifiable--guide scientific progress and underpin our modern cosmological paradigm. This monumental puzzle is far from complete, however, as scientists confront the mysteries of the ultimate causes of cosmic structure formation and the real nature and origin of dark matter and dark energy.

Throughout history, people have tried to construct 'theories of everything': highly ambitious attempts to understand nature in its totality. This account presents these theories in their historical contexts, from little-known hypotheses from the past to modern developments such as the theory of superstrings, the anthropic principle, and ideas of many universes, and uses them to problematize the limits of scientific knowledge. Do claims to theories of everything belong to science at all? Which are the epistemic standards on which an alleged scientific theory of the universe - or the multiverse - is to be judged? Such questions are currently being discussed by physicists and cosmologists, but rarely within a historical perspective. This book argues that these questions have a history and that knowledge of the historical development of 'higher speculations' may inform and qualify the current debate on the nature and limits of scientific explanation.

'fascinating' Brian Cox This is the story of citizen science. Where once astronomers sat at the controls of giant telescopes in remote locations, praying for clear skies, now they have no need to budge from their desks, as data arrives in their inbox. And what they receive is overwhelming; projects now being built provide more data in a few nights than in the whole of humanity's history of observing the Universe. It's not just astronomy either-dealing with this deluge of data is the major challenge for scientists at CERN, and for biologists who use automated cameras to spy on animals in their natural habitats. Artificial intelligence is one part of the solution-but will it spell the end of human involvement in scientific discovery? No, argues Chris Lintott. We humans still have unique capabilities to bring to bear-our curiosity, our capacity for wonder, and, most importantly, our capacity for surprise. It seems that humans and computers working together do better than computers can on their own. But with so much scientific data, you need a lot of scientists-a crowd, in fact. Lintott found such a crowd in the Zooniverse, the web-based project that allows hundreds of thousands of enthusiastic volunteers to contribute to science. In this book, Lintott describes the exciting discoveries that people all over the world have made, from galaxies to pulsars, exoplanets to moons, and from penguin behaviour to old ship's logs. This approach builds on a long history of so-called 'citizen science', given new power by fast internet and distributed data. Discovery is no longer the remit only of scientists in specialist labs or academics in ivory towers. It's something we can all take part in. As Lintott shows, it's a wonderful way to engage with science, yielding new insights daily. You, too, can help explore the Universe in your lunch hour.

General Relativity is a beautiful geometric theory, simple in its mathematical formulation but leading to numerous consequences with striking physical interpretations: gravitational waves, black holes, cosmological models, and so on. This introductory textbook is written for mathematics students interested in physics and physics students interested in exact mathematical formulations (or for anyone with a scientific mind who is curious to know more of the world we live in), recent remarkable experimental and observational results which confirm the theory are clearly described and no specialised physics knowledge is required. The mathematical level of Part A is aimed at undergraduate students and could be the basis for a course on General Relativity. Part B is more advanced, but still does not require sophisticated mathematics. Based on Yvonne Choquet-Bruhat's more advanced text, General Relativity and the Einstein Equations, the aim of this book is to give with precision, but as simply as possible, the foundations and main consequences of General Relativity. The first five chapters from General Relativity and the Einstein Equations have been updated with new sections and chapters on black holes, gravitational waves, singularities, and the Reissner-Nordstroem and interior Schwarzchild solutions. The rigour behind this book will provide readers with the perfect preparation to follow the great mathematical progress in the actual development, as well as the ability to model, the latest astrophysical and cosmological observations. The book presents basic General Relativity and provides a basis for understanding and using the fundamental theory.

- Discover how the ancient language of astrology is completely relevant to your life today. - Appreciate how astrology is a language of meaning that helps you decode your inner reality and outer experience. - Understand how your birth moment encapsulates the `information seed for all that unfolds in your life. - Learn how understanding your birthchart can help you live a bigger life, as a true co-creator.

This book is about how big is the universe and how small are quarks, and what are the sizes of dozens of things between these two extremes. It describes the sizes of atoms and planets, quarks and galaxies, cells and sequoias. It is a romp through forty-five orders of magnitude from the smallest sub-nuclear particles we have measured, to the edge of the observed universe. It also looks at time, from the epic age of the cosmos to the fleeting lifetimes of ethereal particles. It is a narrative that trips its way from stellar magnitudes to the clocks on GPS satellites, from the nearly logarithmic scales of a piano keyboard through a system of numbers invented by Archimedes and on to the measurement of the size of an atom. Why do some things happen at certain scales? Why are cells a hundred thousandths of a meter across? Why are stars never smaller than about 100 million meters in diameter? Why are trees limited to about 120 meters in height? Why are planets spherical, but asteroids not? Often the size of an object is determined by something simple but quite unexpected. The size of a cell and a star depend in part on the ratio of surface area to volume. The divide between the size of a spherical planet and an irregular asteroid is the balance point between the gravitational forces and the chemical forces in nature. Most importantly, with a very few basic principles, it all makes sense. The world really is a most reasonable place.