Seasons

The Zodiac throughout the Year

Example: In Winter sun in Sagittarius, Gemini at night sky; in summer sun in Gemini, Sagittarius at night sky

The Seasons• Change of seasons

is a result of the tilt of the Earth’s rotation axis with respect to the plane of the ecliptic

• Sun, moon, planets run along the ecliptic

Ecliptic horizontal, Celestial equator and Earth axis tilted

Demos

• TeacherTube video• Season apparatus• Wikipedia Icecover

What changes?

• Sun is closer to the celestial north pole in the northern summer– Therefore it is higher in the sky

• Therefore the sunlight hits us more directly– Therefore the energy deposit per unit area is higher

» Therefore the temperature goes up

– Therefore the sun is above the horizon longer• Therefore there is more sunlight per day

– Therefore the temperature goes up

Illumination Angle and Energy density

From Wikipedia

What does not change

• The direction of the Earth’s axis (still points to the CNP)

• The distance to the sun (there is a 1.7% change of the distance to the Sun, but we get closest to the Sun in early January!)

• The fact that we are about an Earth radius closer to the Sun at noon in the summer is negligible (6300km compared to 150 mill.km is 0.004%)