In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the … See more

Celestial spheres (or celestial orbs) were envisioned to be perfect and divine entities initially from Greek astronomers such as Aristotle. He composed a set of principles called See more

These concepts are important for understanding celestial coordinate systems, frameworks for measuring the positions of objects in the sky. Certain reference lines and See more

A celestial sphere can also refer to a physical model of the celestial sphere or celestial globe. Such globes map the constellations on the outside of a sphere, resulting in a mirror … See more

Because astronomical objects are at such remote distances, casual observation of the sky offers no information on their actual distances. All celestial objects seem equally far away, as if fixed onto the inside of a sphere with a large but unknown radius, which See more

The ancient Greeks assumed the literal truth of stars attached to a celestial sphere, revolving about the Earth in one day, and a fixed Earth. The Eudoxan planetary model, … See more

Observers on other worlds would, of course, see objects in that sky under much the same conditions – as if projected onto a dome. Coordinate systems based on the sky of that world could be constructed. These could be based on the equivalent "ecliptic", poles and … See more