Name: ________________________________
TILTING INTO THE SEASONS
Do you live in a place with well-defined seasons? Do you appreciate the change of the seasons, from cold and
dark to hot and bright, over the months? In other words, are you happy that Earth's axis is tilted?
Earth’s Seasons
A common misconception is that the Sun is closer to Earth in the summer and farther away from it during the
winter. Although it is true that the distance between Earth and the sun changes during the course of a year
(remember: Earth’s orbit is an ellipse, not a circle), this does not cause seasons. Think about it, if the distance
between the Earth and the sun would determine seasons, it would be summer on both hemispheres during the
same part of the year. However, we know that when it is summer in the United States, it is winter in Australia.
Instead, the seasons are caused by the 23.5o tilt of Earth’s axis
(Figure 1). The Earth’s tilt on its axis leads to one hemisphere facing
the Sun more than the other hemisphere and gives rise to seasons.
Earth’Draw the axis of Earth’s rotation in Figure 1.
Solar Radiation on Earth
Different parts of the Earth receive different amounts of solar
radiation. Which part of the planet receives the most solar radiation?
The Sun's rays strike the surface most directly at the equator which is
the dotted line located across the center of the Earth (Figure 1).
Figure 1
Different areas also receive different amounts of sunlight in different seasons. What causes the seasons? The
seasons are caused by the direction Earth's axis is pointing compared to the Sun’s location. The Earth revolves
around the Sun once each year and spins on its axis of rotation once each day. This axis of rotation is tilted
23.5o relative to its plane of orbit around the Sun. Draw the plane of Earth’s orbit in Figure 1.
Northern Hemisphere Summer
The North Pole is tilted towards the Sun and the Sun's rays strike the Northern Hemisphere more directly in
summer (Figure 2). At the summer solstice, June 21, the Sun's rays hit the Earth most directly (Figure 3) along
the Tropic of Cancer (23.5oN). These sun rays are strong and heat up that part of the Earth more. When it is
summer solstice in the Northern Hemisphere, it is winter solstice in the Southern Hemisphere.
Figure 2: Summer solstice in the Northern Hemisphere.
Northern Hemisphere Winter
Winter solstice for the Northern Hemisphere happens on
December 21. The tilt of Earth's axis points away from the
Sun (Figure 4). Light from the Sun is spread out over a larger
area, so that area isn't heated as much. With fewer daylight
hours in winter, there is also less time for the Sun to warm the
area.
When it is winter in the Northern Hemisphere, it is summer in
the Southern Hemisphere. In Southern Hemisphere summer,
the Sun’s rays directly strike the Tropic of Capricorn (23.5oS).
Sunlight is spread across a large area near the South Pole. No
sunlight reaches the North Pole.
Figure 4: Winter solstice in Northern Hemisphere.
Equinox
Halfway between the two solstices, the Sun's rays shine most directly at
the equator, called an equinox (Figure 5). The daylight and nighttime
hours are exactly equal on an equinox. The autumnal, or fall equinox
happens on September 22 or 23 and the vernal, or spring, equinox happens
March 21 or 22 in the Northern Hemisphere.
During the summer, areas north of the equator experience longer days and
shorter nights. This is because at this time the Northen Hemisphere is
tilted towards the sun and receives more direct rays. At the same time in
the Southern Hemisphere it is winter and locations will have longer nights
and shorter days. This is because this Hemisphere is pointed away from the
sun and receives less direct rays.
Figure 5: Spring/ Fall Equinox
Season Summary
CAUSE
Earth’s rotational axis is tilted, ________, compared to the plane of revolution.
EFFECT
During one half year Earth’s Northern hemisphere is
tilted ____________ the sun
RESULT
EFFECT
During the other half year the Northern hemisphere
is tilted __________ from the sun
RESULT
The sun’s rays strike the NH more directly and these
_____________________ heat up the NH more.
The sun’s rays strike the NH more indirectly and
these ________________ heat up the NH much less.
(NH receives more than 12 hours of sunlight per day)
(NH receives less than 12 hours of sunlight per day)
SEASONS
__________________&_____________________
SEASONS
__________________ & ___________________
1. If Earth were NOT tilted would we have seasons in Schaumburg or anywhere on Earth? Explain why or
why not.
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2. On what DAY is the North Pole tilted toward the sun the most? ___________________
3. On what DAY is the North Pole tilted away from the sun the most? _________________
4. On what DAY does Spring start in the Northern hemisphere? _____________________
5. On what DAY does Fall start in the Northern hemisphere? _______________________
Read each hypothesis for the occurrence of seasons and explain why they are incorrect. Use
evidence from the text in your answer. (Use A and C in ACE)
6. Seasons are caused by the Earth being closer to the sun in the summer and farther in the winter due to
Earth’s elliptical orbit.
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7. Seasons are caused by the Earth being tilted. In the summer in the Northern hemisphere , Earth is tilted
toward the sun which brings it closer to the sun’s indirect rays of light.
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8. The amount of sunlight each part of Earth receives is constant throughout Earth.
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What causes Earth to have seasons?
Describe two results that are caused by the tilt in earth’s axis and explain
which result is mostly responsible for seasons on Earth.
Use ACE to answer the question. Please use one piece of evidence from the video and the other from the text.
http://ed.ted.com/lessons/reasons-for-the-seasons-rebecca-kaplan
a.
b.
c.
d.
e.
Answer: (Answer and restate the question)
Cite Evidence from video: (In the video it states, …….…)
Cite Evidence from text: (In the text it states, …….…)
Explain: (This means that …)
Connect: (Tie back your answer with what you have learned)
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