Reason for the Seasons Notes
Seasons Vocabulary
Seasons - Due to the tilt of earth as it travels around the Sun, we have spring, summer,
fall, and winter.
Source: http://www.srh.noaa.gov/abq/features/WhatCausesTheSeasons/SummerSolstice2008.php
Earth’s Revolution - The circling of the Earth around the Sun. (The Moon also revolves
around the Earth.) It takes 365 days (one year) for the Earth to revolve once around the
Sun.
Axis
Source: http://www.learner.org/jnorth/tm/ReasonsBack.html
Axis of Rotation - An imaginary line going from the North Pole to the South Pole.
The earth spins on this line.
Earth’s Rotation – The Earth spinning on its axis. It takes the Earth 24 hours (one day)
to revolve one time around its axis.
Source: http://www.physicalgeography.net/fundamentals/6h.html
Earth’s Tilt - The earth’s axis is not straight up and down, instead it leans at a
23.5-degree angle.
Orbit - The path that a planet travels as it goes around the Sun or a moon takes as
it goes around a planet.
Source: http://www.aerospaceweb.org/question/astronomy/q0262.shtml
Direct Sunlight (heat energy) - Covers a small surface area; heat is concentrated and
warmer; Sun is high in the sky; summer heat energy is direct.
Source: http://www.astronomy.org/programs/seasons/
Indirect Sunlight (heat energy) - Covers a large surface area; heat is spread out and
colder; Sun is low in the sky; winter heat energy is indirect.
Source: http://www.astronomy.org/programs/seasons/
http://ag.arizona.edu/watershedsteward/resources/module/Climate/climate-intro_pg2.htm
Why do we have seasons?
 Because the Earth tilts.
 Earth tilts 23.5o.
How does tilt cause seasons?
 Earth Revolves Around Sun.
 Earth tilts towards or away from Sun.
 Earth tilts towards Sun in summer.
 Earth tilts away from Sun in winter.
 Earth doesn’t tilt towards or away from the Sun in spring and fall/autumn.
Very important facts about the seasons.
Earth is closest to the Sun in January (winter).
Earth is farthest from the Sun in July (summer).
The Earth’s distance to the Sun has NO EFFECT ON
WHY WE HAVE SEASONS
Direct and Indirect Sunlight (Heat Energy)
 Direct sunlight (heat energy) is received in the summer.
 Indirect sunlight (heat energy) is received in the winter.
Direct Sunlight
Source: http://www.astronomy.org/programs/seasons/
 We receive direct sunlight (heat energy) when Earth tilts towards the Sun.
 Sunlight (heat energy) is concentrated (it covers a small area of the Earth’s
surface).
 Heat energy warmer.
 Sun is high in the sky.
Indirect Sunlight
Source: http://www.astronomy.org/programs/seasons/
 We receive indirect sunlight (heat energy) when Earth tilts away from the
Sun.
 Sunlight (heat energy) is not concentrated (it covers a large area of the
Earth’s surface).
 Heat energy colder.
 Sun is low in the sky.
Key Season Dates
Event
Date
Seasons
Winter Solstice
December 21st
First Day of Winter
Spring Equinox
March 21st
First Day of Spring
Summer Solstice
June 21st
First Day of Summer
Autumnal Equinox
September 21st
First Day of Autumn/Fall
Key Terms
 Solstice – Dates the Sun is the highest or the lowest in the sky.
 Equinox – “Equal Nights” – Daylight and nighttime hours are equal – about twelve
hours of daylight and about twelve hours of nighttime.
 Winter Solstice – Sun is at the lowest point in the sky. Has the fewest hours of
daylight (“shortest day”) – about eight hours of daylight.
 Summer Solstice - Sun is at the highest point in the sky. Has the most hours of
daylight (“longest day”) – about sixteen hours of daylight.
Seasons Are Reversed
 When Northern Hemisphere is tilting towards the Sun (summer), the Southern
Hemisphere is tilting away from the Sun (winter).
 When Northern Hemisphere is tilting away from the Sun (winter), the Southern
Hemisphere is tilting towards the Sun (summer).
Earth’s Position Around
How Northern and Southern
Season in Northern and
Sun
Hemisphere Tilt
Southern Hemisphere
North– Tilts way from Sun.
South – Tilts towards from Sun.
North – Winter
South – Summer
Neither Hemisphere tilts
towards/away from Sun.
North – Spring
South – Autumn/Fall
Seasons Are Reversed
 When Northern Hemisphere is tilting towards the Sun (summer), the Southern
Hemisphere is tilting away from the Sun (winter).
 When Northern Hemisphere is tilting away from the Sun (winter), the Southern
Hemisphere is tilting towards the Sun (summer).
Earth’s Position Around
How Northern and Southern
Season in Northern and
Sun
Hemisphere Tilt
Southern Hemisphere
North– Tilts toward Sun.
South – Tilts away from Sun.
North – Summer
South – Winter
Neither Hemisphere tilts
towards/away from Sun.
North – Autumn/Fall
South – Spring