300 Astronomical Objects: A Visual Reference to the Universe (Firefly Visual Reference) - Hardcover

Wilkins, Jamie; Dunn, Robert

Hardcover

ISBN 10: 1554071755 ISBN 13: 9781554071753

Publisher: Firefly Books, 2006

Synopsis

A handy and comprehensive reference to the 300 most interesting celestial objects.

This book provides a tour through the galaxy, from its solar core to its outer limits, with all the highlights and the very latest data about the universe.

Convenient data sidebars with each entry provide facts and figures on every object- including mass, magnitude, density, radius, rotation period, and surface and core temperatures. An annotated cross-section of the object enhances this information, and a full-page photograph brings the object to life.

Additional spreads bring together and explain related objects or phenomena. For example, the corresponding pages for the sun include solar power, sunspots and solar flares. Others examples include:

• Mercury: Mercury's surface
• The asteroid belt: Eros 433
• Jupiter's moons: 10, Europa, Callista
• Uranus: Uranus' rings, Ariel and Titania
• Outer belts and comets: Halley's comet; Deep Impact
• Space telescopes: International Space Station.

300 Astronomical Objects is a handy reference for the amateur astronomer.

About this title

About the Author

Jamie Wilkins has a degree in astrophysics from Cambridge University.

Robert Dunn has a degree in natural sciences, specializing in physics, from Cambridge University, where he is a researcher at the Institute of Astronomy.

Excerpt. © Reprinted by permission. All rights reserved.

Introduction

0ne of the biggest challenges to humanity in understanding the universe is coming to terms with the immense scales involved. Our minds have developed to deal with local geography, such as the rivers and hills around a settlement. As we made the transition from a tribal to a global species, we explored Earth. About 3,000 years ago, at the time of the Greek poet Homer, maps of the world consisted only of the Mediterranean and its neighboring land. Earth itself was thought to be a flat body of land surrounded by unknown seas.

Scientific advancement pushed back the geographical boundaries. While investigating shadows cast by sticks at noon on a summer solstice at two places 500 miles (800 km) apart, Greek philosopher Eratosthenes (c.276-c.194 B.C.) determined that Earth's surface must be curved. On a flat Earth, the sticks' shadows would have been equal, but they were not. Furthermore, he was able to estimate Earth's circumference to be about 25,000 miles (40,000 km). This new understanding of the world prompted sailors and explorers to imagine circumnavigating the globe.

Of course humanity looked not only north, south, east, and west, but also up into the sky. The regularity of the passage of the Sun, the Moon, and the stars was understood well before people began keeping records. This led to an understanding of time and the passage of the seasons. Ancient monuments such as Stonehenge in England are aligned in a way that suggests they were used to calculate the annual calendar.

The motion of the skies was crucial to the survival of early societies and they attached great significance to them. Changes in the skies were thought to be omens. The practice of interpreting omens from the heavens is known as astrology. Throughout most of their recorded history, rulers in China paid great attention to their court astrologers. Huge effort was put into observing the heavens and recording the various phenomena, and China produced the earliest known records of events such as solar eclipses and comets. Texts describing every return of Halley's Comet for 2,000 years have helped modern astronomers refine their understanding of its orbit. References to sunspots provide us with information on potential long-term variations in the output of power from the Sun. The famous Crab Nebula is the remnant of a supernova explosion that was documented by Chinese court astronomers in 1054.

Earth-Centered Universe

Astrology was by no means unique to the Chinese. Scientific study of the universe was typically driven by a desire to understand the future rather than the universe itself. The Ancient Greek philosophers used the stars to predict events. One of the greatest was Aristotle (384-322 BC), who studied almost every subject known at the time and produced many books in which he put forward his views. His concept of the universe was geocentric: Earth was stationary at the center, and the planets, the Moon, and the Sun were in orbit around it. He stated that the heavens (the sky) were perfect and incorruptible, unlike Earth. The path of the planets must therefore take the form of a circle, which was the most perfect shape known. Not all of Aristotle's pronouncements relied on real evidence, and in this case the observed motion of the planets was incompatible with his simple model. Viewed over several weeks, the path of a planet in Aristotle's system would simply trace a curved line across the sky. In reality, Mars, Jupiter, and Saturn all appear to slow down at times in their prescribed routes, and even go backward for a while (retrograde motion). To reconcile this apparent discontinuity, the concept of epicycles was proposed, whereby each planet moved in a circle (an epicycle), the center of which (known as the deferent) itself described a larger circle around Earth. This theory of the universe was codified by Ptolemy (c.100-c.1 70) in his treatise on astrology.

Arabic Astrology

The line of Greek philosophers died out at this point, and Europe underwent a period known as the Dark Ages. The great library at Alexandria, the storehouse of ancient knowledge, was lost. Ptolemy's treatise survived, however, as an Arabic translation entitled the Almagest. Arabic civilizations drew on Ptolemy's work to refine their own brand of astrology and to achieve accurate timekeeping that was essential for their prayer times. Elaborate and accurate astrolabes followed, enabling followers of Islam to know the direction of Mecca.

Arabic astronomers soon improved on the Almagest, especially in the area of star catalogs. Most of the names we use for stars today come from the Arabic language, although often corrupted by the passage of time. (For example, the name Acubens, the Alpha star of Cancer, comes from the Arabic al zubanah, meaning "the claws.") While the precision of astronomical knowledge was greatly enhanced during this time, the geocentric cornerstone of the Ptolemaic system was not successfully challenged. After the chaos resulting from the fall of the Roman Empire had cleared, astronomical knowledge flooded back into Europe through texts translated from Arabic. The survival of Greek geometry alongside Arabic numerals and algebra was essential for what followed.

Sun-Centered Universe

Although Polish astronomer Nicolaus Copernicus (1473-1543) was not the first person to conceive of a heliocentric (Sun-centered) universe, he is credited away from the beliefs of Ptolemy and Aristotle. In his controversial book De Revolutionibus he argued that the Earth moved, rotating on its own axis as well as orbiting the Sun. The other planets also orbited the Sun, and Copernicus correctly calculated their order, placing Earth between Venus and Mars. This simple alteration solved several of the issues surrounding the Ptolemaic system, which had remained the accepted model for 1,700 years. Unsurprisingly, it was not well received, and Copernicus was criticized in print by many who believed his theories to be an attack on religion itself.

Elliptical Orbits of the Planets

Despite the advances made after Ptolemy's time, the charts and tables that were used to predict planetary motions were still inaccurate, partly because they used circular orbits and partly because they were based on imprecise observations. A Danish astronomer, Tycho Brahe (1546-1601), improved on previous attempts, in particular with measurements of the movement of Mars. His accuracy was all the more amazing since the telescope had not yet been invented. He was also a witness to the supernova of 1572, known thereafter as Tycho's Star. It was another nail in the Ptolemaic view of the world -- the Ancient Greeks had taught that the heavens were constant and unchanging (comets were seen as simply atmospheric phenomena).

Shortly before he died, Tycho was joined by an assistant, the German mathematician Johannes Kepler (1571-1630). Armed with Tycho's observational data, Kepler was able to construct a new model of the universe. Kepler's breakthrough was the realization that the orbits of the planets are not perfect circles but are slightly elliptical. He formulated his ideas as a set of mathematical laws that also related each planet's orbital period to its distance from the Sun.

Galileo

Overlapping the careers of Tycho and Kepler was the life of Italian scientist Galileo Galilei (1564-1642). His use of experimentation and observation was in direct contrast to the Aristotelian methods of arguing the nature of reality from pure reason. Sometime in the first decade of the 17th century the telescope was invented in Holland. Galileo heard about this new invention and proceeded to construct telescopes of his own, improving the quality and power in each one he built.

The increased vision from the telescopes showed Galileo that there were many more stars in the sky than any unaided observer would ever have guessed. The Milky Way was resolved into a dense region of stars rather than the cloudlike object it was previously believed to be. Galileo sa

Edition details

• Publisher: Firefly Books
• Publication date: 2006
• ISBN 10: 1554071755
• ISBN 13: 9781554071753
• Binding: Hardcover
• Language: English
• Number of pages: 528