The Science Of Astronomy

Definition

· Astronomy is the study of all matter and energy in the universe, with emphasis on the concentration of this matter and energy in evolving bodies such as planets, stars, and galaxies. Moreover, the science of astronomy helps us to recognize that humanity is part of the universe, and that our home, the Earth, is only one of the many places in the universe, but also the special point from which our voyage of exploration begins 1.

· The word astronomy is built on Greek roots: “astron” meaning star and “nomos” meaning arrangement, order, or law.

Origin

· Astronomy is the oldest of the sciences, with roots extending as far back as recorded history. Ancient people made careful and detailed observations of the sky. In part, it was probably because they were just as curious and intelligent as we are now. In the daytime, they surely recognized the importance of the Sun to their lives. At night, without electric lights, they were much more aware of the starry sky than we are today. (“Light pollution” produced by electric lights seriously interferes with astronomical observations 2.) Therefore, it’s not surprising that they paid attention to patterns of motion in the sky and developed ideas and stories to explain what they observed. In fact, events in the sky affected ancient people more so than they influence us today.

· Time Keeping – Astronomy played a practical role in ancient societies by enabling them to keep track of time and seasons, a crucial skill for people who depended on agriculture (planting and harvesting of crops) for survival. This ability may seem outdated today, when digital watches tell us the precise time and date, but it required considerable knowledge and skill in ancient times, when the only clocks and calendars were in the sky.

· Modern measures of time still reflect their ancient astronomical roots. Our 24-hour day is the time its takes the Sun to circle the sky. The length of the month comes from the Moon’s cycle of phases, and our calendar is based on the cycle of the seasons. The days of the week are named after the seven naked-eye objects that appear to move among the constellations: the Sun, the Moon, and the five planets (Mercury, Venus, Mars, Jupiter, and Saturn) recognized in ancient times.

· Celestial Navigation – Celestial navigation utilizes the Sun and the stars to find one’s position on Earth. For example, hundreds of years ago, the peoples of Polynesia and Micronesia were among the most skilled navigators in the world. They were able to guide their wooden vessels accurately across vast stretches of the Pacific, far beyond the sight of land. Their secret was to watch the positions of certain stars such as Alpha and Beta Centauri and the Southern Cross. Each of these stars rises and sets at the same points on the horizon every night. Pacific navigators used these rising and setting points much as a modern sailor uses the points of a compass.

· The full Moon lit the way for travelers at night. Today with nighttime lighting such as streetlights and automobile headlights, it is not necessary to depend on the Moon’s light to travel at night.

· Astrology – Astronomy is a science, whereas astrology is not. Today the two subjects are very different from one another, but hundreds of years ago astronomy and astrology were linked. Astrology began about 4000 years ago in the religions of Babylonia that believed the future of the nation and ruling class depended on the planets, Sun, and Moon and their motions. Astrology spread through most of the western world when the Greeks became the world power and incorporated the Babylonian culture into their own. The application of astrology expanded to all social classes. Eventually, people came to believe that the position of the planets, Sun, and Moon at a person’s birth was especially significant. Astronomy broke away from astrology and developed into a science when it became more important to explain what made the planets move the way they do and not in predicting the future and interactions of individuals.

Tools

· Ancient Structures – Remains of structures indicate an awareness of naked-eye astronomy by the peoples of many ancient cultures. For example, four to five thousand years ago, the inhabitants of the British Isles erected stone structures, such as Stonehenge 3, that suggest a preoccupation with the motions of the sky. Alignments of these stones appear to show where the Sun rose and set at key times during the year. Another example was built a thousand years ago in the Mayan city of Chichén Itzá, on the Yucatán Peninsula. The Caracol’s cylindrical tower 4 contains windows aligned with the northernmost and southernmost rising and setting points of both the Sun and the planet Venus.

· Before such structures could be built, careful observations had to be made and repeated over and over to ensure validity. Careful, repeatable observations also underlie the modern scientific method. To this extent, elements of modern science were present in many early cultures.

· Telescopes – The telescope is by far the most useful tool that astronomers have for collecting data about the universe. Large telescopes, such as those atop Mauna Kea in Hawaii 5, make images that are far brighter and sharper than the images formed by our eyes. A number of modern telescopes can even adjust for the “twinkling” of starlight, which occurs when light passes through turbulent air (adaptive optics). Some telescopes deal with this problem by avoiding it altogether; the most famous example is the Hubble Space Telescope 6, which orbits high above the blurring effects of the atmosphere. Other telescopes on Earth and in orbit explore the electromagnetic spectrum at wavelengths outside the visible range, such as radio and x-ray telescopes. Optical telescopes come in two basic designs: refracting and reflecting.

· Refracting Telescope – A refracting telescope operates much like an eye, using transparent glass lenses to focus the light from distant objects. The earliest telescopes were refracting telescopes. The largest refracting telescope is located at Yerkes Observatory in Chicago 7. It has a lens that is 40 inches in diameter and a telescope tube that is 64 feet long.

· Reflecting Telescope – A reflecting telescope uses a precisely curved mirror to gather and focus light. The largest reflecting telescope (single-piece) is the Subaru telescope located at top of Hawaii’s Mauna Kea 8. It has a mirror that is 27.25 feet in diameter. Today, most astronomical research involves reflecting telescopes.

· Spacecraft – With few exceptions, such as the Space Shuttle, the Space Station, and the Apollo missions to the Moon, nearly all spacecraft are robotic, meaning that no humans are aboard. Their operations are partly automated and partly controlled by scientists who send instructions via radio signals from Earth. Most robotic spacecraft fall into three main categories: flybys, orbiters, and probes and landers.

· Flybys – A flyby is a spacecraft that flies past a world just once and then continues on its way. For example, Voyager 2’s 9 flight path allowed it to make flybys of Jupiter, Saturn, Uranus, and Neptune.

· Orbiters – An orbiter is a spacecraft that goes into orbit around a world. For example, Cassini orbiter 10 began a four-year mission in July of 2004 that includes more than 70 orbits around the planet Saturn and its moons.

· Probes and Landers – The most “up close and personal” study of other worlds comes from spacecraft that sends probes into their atmospheres or landers to their surfaces. For example, the Mars Exploration Rovers 11 act as robot geologists on the surface of Mars.

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