Because astronomical objects are at such remote distances, casual observation of the sky offers no information on … 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 Aristotelian physics that outlined the natural ord… 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 planes on Earth, when projected onto the celestia… See more

The ancients 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, on which the Aristotelian and Ptolemaic models wer… 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 image of the constellatio… 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 coul… See more

• Horizontal coordinate system
• Equatorial coordinate system
• Equinox (celestial coordinates)
• Spherical astronomy… See more