1. Rotating Earth
Sunlight
animations © Swinburne

2. Star Trails due to Earth’s Rotation

3. The Celestial Sphere and Celestial Poles
north celestial pole
The Celestial Sphere and Celestial Poles
Celestial Sphere
south celestial pole

4. … which is an extension of the Earth’s equator.
north celestial pole
“celestial equator”
… which is an extension of the Earth’s equator.
south celestial pole

5. We can also project the Earth’s imaginary longitude
north celestial pole
We can also project the Earth’s imaginary longitude
and latitude lines onto the celestial sphere
The corresponding celestial coordinates are:
Longitude  right ascension (RA)
Latitude  declination (dec)
south celestial pole

6. Phases as seen from Earth
Phases of the Moon
Third quarter A B C D E F G H
Sun’s
rays
New moon
Full moon
First quarter
A B C D E F G H
Phases as seen from Earth

7. The Earth Orbits Around the Sun
The Earth takes one year to make a complete orbit around the Sun.

8. 1 AU = distance between Earth and Sun = 1.495979 x 108 km

9. zodiacal constellations

13. The Earth’s rotational axis is tilted by 23
The Earth’s rotational axis is tilted by 23.5° with respect to a line drawn perpendicular to the plane of the ecliptic.
23.5°
Earth’s rotation axis
plane of the ecliptic

14. Let’s have a look how it works during the course of a year:
northern spring
northern summer
northern hemisphere winter
southern autumn
southern winter
northern autumn
southern hemisphere summer
southern spring

15. Northern hemisphere in summer ...
equator
rotation axis
sunlight