Applied Science: Unit 14 A- astronomy and space science

Astronomy And Space Science: Stellar Astronomy Scientific Thought: In Context COPYRIGHT 2009 Gale Astronomy and Space Science: Stellar Astronomy Introduction Stellar astronomy is the study of the sun and the stars: what they are, how they move, and how they are born, live, and die. The major challenge of this field is the staggering distance to even the closest stars. Scientists had great difficulty understanding stars without being able to touch them and experiment upon them. This difficulty required radical, creative thinking and a constant willingness to embrace new ideas and techniques. Historical Background and Scientific Foundations The motion of the sun, both on a daily and annual basis, is one of the most basic human observations of the sky. Most ancient civilizations developed techniques of varying sophistication for tracking, recording, and predicting these motions for agricultural and ritual purposes. Some devices have survived in the form of structures, such as Stonehenge in England. Buy Solar Panel Accessories ­ Orders Over $50 Ship Free Find All The Solar Panel Accessories Products You Need at Z! Orders Over $50 Ship Free on All Solar Panel Accessories at Z! | Sponsored▼ Greek astronomers only investigated the stars as points against which to measure the motion of the planets. Despite their limited ASTRONOMY AND SPACE SCIENCE tools, Greek astronomers were able to make impressive estimates of the size and distance to the sun. Aristarchus of Samos (c.310– c.230 BC) used the geometry of eclipses to calculate that the sun was roughly 19 times as far away from Earth as the moon, and that the sun was about 6fl the size of Earth. These numbers are far smaller than modern values, but represent a significant achievement of mathematics for their day. Report Advertisement Physical understandings of the sun and stars were codified by the Greek philosopher Aristotle (384–322 BC), whose cosmological system remained intact and in use for nearly two thousand years. Aristotle described the universe as a series of nested spheres, with Earth at the center and the fixed stars at the outside. A critical element of Aristotle's system was the lunar boundary: below the boundary was the world of earth, air, fire, and water—a world that was marked by constant change—and above it everything was perfect and unchanging in every way. Thus both the sun and the stars, being above the boundary, were thought to not change over time (other than their circular motion). Any changes in the sky, such as meteors, were assumed to be atmospheric phenomena. Best Automatic Chicken Door ­ Solar or plug­in options Best selling. Aluminum construction. Fast delivery & great customer service. | Sponsored▼ The Sun at the Center Two factors, conceptual and observational, combined in the sixteenth and seventeenth centuries to make the sun a focus of interest. The first was the emergence of the idea that the sun was in some way special. The stimulus for this elevation of the sun's significance is usually attributed to the Polish astronomer Nicolas Copernicus (1473–1543), whose cosmological system placed the sun at the center of the universe. Copernicus' motivations were complex, but he argued that the sun was the most important celestial body and that a central location was more fitting: “At rest, in the middle of everything, is the Sun. For in this most beautiful temple, who would place this lamp in another or better position than that from which it can light up everything at the same time?” One of Copernicus' most ardent followers, the German astronomer Johannes Kepler (1571–1630), thought the central location of the sun had important physical and theological significance. He thought it might provide a physical force that moved the planets. He made little progress with this idea, but it provided the foundational concept that the sun had physical effects on the planets. From his cultural background, Kepler also saw Christian theological meaning in the structure of the Copernican cosmos. The Parallax Problem Report Advertisement Few of the early Copernicans gave serious thought to the nature of the stars, but their cosmology did make an important prediction about their appearance. If, as Copernicus claimed, the Earth moved, then astronomers should be able to observe a phenomenon known as stellar parallax. Parallax is the apparent motion of a nearby object relative to a distant one as viewed by an observer who is also in motion. An observer on a moving Earth should be able to see nearby stars moving relative to distant stars on an annual basis. This was not observed, however, and that meant either that Copernicus was wrong, or the universe was vastly larger than previously assumed, since parallax decreases with the distance of the observed objects. In the years between Copernicus and Kepler, dramatic advances were made in astronomical technology and technique that helped overturn the Aristotelian understandings of stars and the sun. One of the major figures was the Danish astronomer and aristocrat Tycho Brahe (1546–1601). Tycho acquired an entire island and used tremendous resources to build a sophisticated observatory with massive versions of traditional instruments such as the quadrant. His observations were vastly more accurate than any made before, and two observations made a particular impact. The first was in 1572 when he saw that a new star had appeared in the sky (a nova); the second was a comet in 1577. Using his uniquely precise tools and methods, Tycho was able to convincingly demonstrate that both of these phenomena Must have been above the moon. This indicated the celestial realm was not unchanging as Aristotle had predicted. It is interesting to note that the 1572 nova was the first recorded in western astronomy, but several novae had been previously observed and recorded by Chinese astronomers. This is a striking example of how sometimes people, even trained astronomers, see only what they expect to see: since Aristotle said changes among the stars were impossible, observations of such changes were simply rejected. Report Advertisement A generation after Tycho, the Italian astronomer Galileo Galilei (1564–1642) improved the design of the telescope, a new tool invented in the Netherlands. He turned his telescope to the night sky, observing a variety of phenomena not previously recorded. He found that where the planets appeared as disks in the telescope, the stars remained as tiny points. He interpreted this to mean that they were much farther away than the planets, which he used to explain his failure to detect the stellar parallax expected by Copernicus' theory. Through his telescope he also saw new stars that dramatically expanded the scope of the universe. While examining the sun, Galileo found that it was not perfect, as the Aristotelian system demanded. In the summer of 1612 he followed in the footsteps of the Jesuit astronomer Christoph Scheiner (1573–1650) and others by using his telescope to explore the surface of the sun. All of these men saw strange dark patches On the sun, which came to be called sunspots. These spots traveled across the sun, sometimes breaking into smaller spots or disappearing entirely. Galileo argued that this was evidence that the sun was imperfect and changing, while Scheiner provided a variety of alternative interpretations. Galileo's investigations persuaded many people that the Aristotelian explanations of the sun and stars were lacking. The seventeenth century saw a number of important figures advancing completely new views regarding the composition of the sun and of its place in the solar system. Most important was the French philosopher René Descartes (1596–1650) who postulated that the sun sat at the center of an enormous vortex of moving particles that carried the planets in their orbits. He also proposed that the stars seen in the night sky were identical to our sun and sat at the center of their own vortices filled with planets. Descartes' vision expanded the scope of the universe to infinity, even implying that there could be many inhabited worlds around other stars.