Transcript SeasonsPPT
Seasons on Earth
Butler Middle School 8th Grade Science Bob, Paul, Ms Adams, Oct 25, 2012
8th Grade Science
The Observed Data: 4 Seasons
Autumn or Fall Winter Spring Summer
We can explain the 4 seasons using Models of the Earth and Sun
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
Spherical Earth Model
Equator Earth rotates on N-S axis once per day
Earth-Sun Model
(evolved over 100’s maybe 1000‘s of years) Earth revolves around the sun once per year + a little bit
Earth
’
s Orbital Plane Points to Polaris (North Star) to Polaris orbital plane 7 perpendicular to orbital plane
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: 365 days + 1/4 day Leap Year - Every 4 years February has an extra day 4 years = (365 + 365 + 365 + 366) = 1461 days
Comparing Diameters Earth Sun
Sun ≈ 109 x Earth
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
Energy distribution from Sun
S
slanted hit
U
direct hit
N
large area (cooler) small area (warmer)
Energy distribution from Sun
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!
Understanding Summer and Winter Summer in the North ☺
S
Winter in the North ☹ ☺ night day
U
☹ South
N
South From summer to winter earth revolves half-way around Sun
Special Days
Vernal Equinox March 20 Winter Solstice Dec 21 Summer Solstice June 21 Vernal Equinox Autumnal Equinox Sept 22
Earth Sun Model
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