1. Seasons on Earth Butler Middle School 8th Grade Science
Bob, Paul, Ms Adams, Oct 25, 2012

2. The Observed Data: 4 Seasons
Autumn or Fall
Winter
Spring
Summer
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3. We can explain the 4 seasons using Models of the Earth and Sun

4. Scientific Model
Representation of an object for study and understanding (very common in Science)
Models can be physical and/or conceptual Model leg in 7th grade life science Computer model of a large weather system

5. Spherical Earth Model
Equator
Earth rotates on N-S axis once per day

6. Earth-Sun Model (evolved over 100’s maybe 1000‘s of years)
Earth revolves around the sun once per year + a little bit

7. Earth’s Orbital Plane to Polaris perpendicular to orbital plane
Points to Polaris
(North Star)
to Polaris
orbital plane
perpendicular
to orbital plane 7

8. Rotate and Revolve
Rotation: spinning like a top Earth rotates on its axis once per 24hr Causes day & night
Revolution: 1 object moving around a 2nd object Earth revolves around sun once per year: days + 1/4 day
Leap Year Every 4 years February has an extra day
4 years = ( ) = 1461 days

9. Comparing Diameters Earth Sun
Sun ≈ 109 x Earth

10. Sun illuminates Earth
The Sun is a huge ball of fire - sends energy (light & heat) to the earth
- 1/2 of earth is always illuminated - day - 1/2 of earth is always in the dark - night

11. Energy distribution from Sun
slanted hit
large area
(cooler) U
direct hit
small area
(warmer) N

12. Energy distribution from Sun

13. Understanding the Seasons
It’s all in the tilt
Summer: - Earth is tilted toward the sun, we get a more direct hit, so it’s warmer
Winter: Earth is tilted away from the sun, we get a slanted hit, so it’s cooler
No tilt means 1 Season!

14. Understanding Summer and Winter
Summer in the North
Winter in the North ☺ ☹ S ☺ ☹ U
night
day N
South
South
From summer to winter earth
revolves half-way around Sun

15. Special Days Vernal Equinox March 20 Winter Solstice Dec 21 Summer
June 21
Autumnal Equinox
Sept 22
Vernal Equinox
March 20

16. Earth Sun Model