THE SKY ABOVE
Our senses suggest to us that Earth is that the center of the universe—the hub around which the heavens turn. This geocentric (Earth-centered) view was what almost everyone believed until the ecu Renaissance. After all, it’s simple, logical, and seemingly self-evident. Furthermore, the geocentric perspective reinforced those philosophical and non secular systems that taught the unique role of citizenry because of the central focus of the cosmos. However, the geocentric view happens to be wrong. One of the good themes of our intellectual history is that the overthrow of the geocentric perspective. Let us, therefore, take a glance at the steps by which we reevaluated the place of our world within the cosmic order.
The Celestial Sphere
If you continue a camping trip or live far away from city lights, your view of the sky on a transparent night is just about just like that seen by people all over the world before the invention of the telescope. Gazing up, you get the impression that the sky may be a great hollow dome with you in the middle , and every one the celebs are an equal distance from you on the surface of the dome. The top of that dome, the purpose directly above your head, is named the zenith, and where the dome meets Earth is named the horizon. From the ocean or a flat prairie, it’s easy to ascertain the horizon as a revolve around you, but from most places where people live today, the horizon is at least partially hidden by mountains, trees, buildings, or smog.
If you lie back in an open field and observe the night sky for hours, as ancient shepherds and travelers regularly did, you’ll see stars rising on the eastern horizon (just because the Sun and Moon do), moving across the dome of the sky within the course of the night, and setting on the western horizon. Watching the sky turn like tonight after night, you would possibly eventually get the thought that the dome of the sky is basically a part of an excellent sphere that is turning around you, bringing different stars into deem it turns. The early Greeks regarded the sky as just such a sphere . Some thought of it as an actual sphere of transparent crystalline material, with the celebs embedded in it like tiny jewels.
Celestial Poles and Celestial Equator
To help orient us within the turning sky, astronomers use a system that extends Earth’s axis points into the sky. Imagine a line browsing Earth, connecting the North and South Poles. This is Earth’s axis, and Earth rotates about this line. If we extend this imaginary line outward from Earth, the points where this line intersects the sphere are called the north pole and therefore the south pole . As Earth rotates about its axis, the sky appears to show within the other way around those celestial poles. We also (in our imagination) throw Earth’s equator onto the sky and call this the equinoctial circle . It lies halfway between the celestial poles, even as Earth’s equator lies halfway between our planet’s poles.
Now let’s imagine how riding on different parts of our spinning Earth affects our view of the sky. The motion of the sphere depends on your latitude (position north or south of the equator). First of all, notice that Earth’s axis is pointing at the celestial poles, so these two points within the sky don’t appear to show . If you stood at the North Pole of Earth, for instance , you’d see the north pole overhead, at your zenith. The equinoctial circle , 90° from the celestial poles, would lie along your horizon. As you watched the celebs during the course of the night, they might all revolve around the pole , with none rising or setting. Only that half the sky north of the equinoctial circle is ever visible to an observer at the North Pole . Similarly, an observer at the South Pole would see only the southern half the sky.