Charting The Heavens

The Foundation of Astronomy

One of the most awe-inspiring sights in the universe is that of a spiral galaxy. Here, this face-on view of the galaxy NGC 1232, located in the southern constellation Eridanus, shows its spread of stars, gas, and dust over a vast expanse some 150,000 light-years across. Despite its distance of about 100 million light-years, modern telescopes allow study of its intricate details—including the older, reddish stars in the central regions and the younger, bluish stars in its spiral arms. (ESO)

The Big Picture: Galaxies are candidates for the grandest, most beautiful structures in the universe. They are colossal collections of typically a hundred billion stars, held together by gravity within one loose structure. There are approximately 40 billion galaxies in the observable universe. One of the great unsolved mysteries in science is the fact that astronomers do not fully understand how galaxies originated.

LEARNING GOALS

Studying this section will enable you to:

Explain the concept of the celestial sphere and the conventions of angular measurement that enable us to locate objects in the sky.

Describe how the Sun, the Moon, and the stars appear to change their positions from night to night and from month to month.

Account for these apparent motions in terms of the actual motions of Earth and the Moon.

Show how the relative motions of Earth, the Sun, and the Moon lead to eclipses.

Explain the simple geometric reasoning that allows astronomers to measure the distances and sizes of faraway objects.

Nature offers no greater splendor than the starry sky on a clear, dark night. Silent and jeweled with the constellations of ancient myth and legend, the night sky has inspired wonder throughout the ages—a wonder that leads our imaginations far from the confines of Earth and the pace of the present day, and out into the distant reaches of space and cosmic time itself. Astronomy, born in response to that wonder, is built on two of the most basic traits of human nature: the need to explore and the need to understand. Through the interplay of curiosity, discovery, and analysis—the keys to exploration and understanding—people have sought answers to questions about the universe since the earliest times. Astronomy is the oldest of all the sciences, yet never has it been more exciting than it is today.