Here we show the (imaginary) celestial sphere around Earth, on which objects are fixed, and which rotates around Earth on an axis. From the sea or a flat prairie, it is easy to see the horizon as a circle around you, but from most places where people live today, the horizon is at least partially hidden by mountains, trees, buildings, or smog.įigure 2.3 Circles on the Celestial Sphere. The top of that dome, the point directly above your head, is called the zenith, and where the dome meets Earth is called the horizon. Gazing up, you get the impression that the sky is a great hollow dome with you at the center ( Figure 2.2), and all the stars are an equal distance from you on the surface of the dome. If you go on a camping trip or live far from city lights, your view of the sky on a clear night is pretty much identical to that seen by people all over the world before the invention of the telescope. Let us, therefore, take a look at the steps by which we reevaluated the place of our world in the cosmic order. One of the great themes of our intellectual history is the overthrow of the geocentric perspective. However, the geocentric view happens to be wrong. Furthermore, the geocentric perspective reinforced those philosophical and religious systems that taught the unique role of human beings as the central focus of the cosmos. After all, it is simple, logical, and seemingly self-evident. This geocentric (Earth-centered) view was what almost everyone believed until the European Renaissance. Our senses suggest to us that Earth is the center of the universe-the hub around which the heavens turn. Understand the modern meaning of the term constellation.Describe how motions of the Sun, Moon, and planets appear to us on Earth.
Describe how motions of the stars appear to us on Earth.Explain the system astronomers use to describe the sky.Define the main features of the celestial sphere.By the end of this section, you will be able to:
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