The celestial sphere, the coordinates system, seasons ...

The celestial sphere, the coordinates system, seasons, phases of the moon and eclipses

Chapters 2 and S1

The celestial sphere and the coordinates system

Chapter S1

How to find our way in the sky? Let's start with the Earth Coordinate System

Latitude: N-S of the equator, Longitude: E-W along equator

From Earth to Space

The Celestial Sphere

? The Celestial Sphere: An

imaginary sphere of infinite

radius centered on Earth. ? The extensions of the Earth

North Celestial Pole

North and South Pole define

the North and South celestial

poles.

? The projection of Earth equator defines the Celestial equator.

? Celestial Sphere can then be divided into a grid, just like the Earth is divided into a grid of latitude and longitude.

North celestial poleNorth

Celestial Equato r

South Celestial Pole

The Celestial Sphere: Motions

? Stars, planets and Sun are "attached" to this imaginary sphere.

? As the Earth rotates, the celestial sphere (with the stars attached to it) appears to rotate in the opposite direction.

? To explain the daily motions of the sky you can imagine the sphere rotating once in 23 hours 56 minutes (using a star as reference).

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