Transcript Earth in Space

Earth in Space
Chap 15, Sec 1
Essential Questions – Chap 15,
Sec 1
1. How
does Earth move
in space?
2. What causes the
cycle of seasons on
Earth?
Astronomy
The study of the moon, stars, and other
objects in space
 Ancient Egyptians were some of the first
people to study astronomy in about 3000
B.C. – or 5000 years ago
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They understood the appearance of Sirius (a
very bright star) in the morning sky indicated it
was almost time for the Nile to flood and then
they could begin planting
How Earth Moves in Space
To us, it appears that both the Sun and
Moon move around the Earth each day.
We see them rise in the east and set in the
west.
 Long ago, people believed this was
exactly what happened – that
EVERYTHING in space circled around
Earth.
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Today we know better
Earth moves through space in
two major ways:
1.Rotation
2.Revolution
Rotation
The spinning of Earth on its axis
 Causes day and night
 One rotation takes approximately 24 hours
– this is called a DAY
 Rotation of the Earth eastward causes the
Sun to appear to move across the sky to
the west

Revolution
The movement of one object around another
 One complete revolution of Earth around the
Sun is called a year and takes 365 ¼ days
 The path of revolution is called orbit. Earth’s
orbit is an ellipse – slightly oval, not a perfect
circle
 Why do we have leap years?
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Every four years we add together the ¼ days and
make one extra day. It keeps us on schedule with
seasons. Otherwise, we would eventually be
having summer in December.
Can you remember . . .
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What causes seasons?
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How does the angle of sunlight affect heating?
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Earth is tilted on its axis
Sunlight hits the equator directly for long periods of time
(days are long)
Areas nearer the poles receive sunlight at a great angle
and for short periods of time (days are short), which
means they get less energy and less heat
What season is it if the southern hemisphere is
tilted towards the Sun?
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Southern hemisphere experiences summer, while we in
the northern hemisphere experience winter
Earth in June

The north end of Earth’s axis is tilted
toward the Sun – it is summer in the
Northern Hemisphere
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Noon sun is high in the sky and there are
more hours of daylight than dark
The Southern Hemisphere is tilted away
from the sun and they are having winter
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The sun is low in the sky and days are shorter
than nights
Earth in December
The Southern Hemisphere now receives
the Sun’s rays more directly and days are
longer than nights – it is summer there
 The Northern Hemisphere is receiving
sunlight at very steep angles and days are
shorter than nights – it is winter there
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Solstices
The two days each year when the sun
reaches its greatest distance north or
south of the equator.
 Around June 21 is OUR summer solstice:
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The sun is farthest north of the equator
 It is the longest day of the year for us in the
Northern Hemisphere
 At the same time, in the Southern
Hemisphere, it is their winter solstice
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Around December 21 is OUR winter
solstice:
The sun reaches farthest south of the equator
 It is the shortest day of the year for us in the
Northern Hemisphere
 At the same time, the Southern Hemisphere is
experiencing their summer solstice and
longest day of the year
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Equinoxes
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These are the two days each year when neither
hemisphere is tilted toward or away from the sun.
The noon sun is directly overhead at the equator
Equinox means “equal night”
Day and night are each about 12 hours long
everywhere on Earth
Around March 21 is spring equinox for the
Northern Hemisphere
Around September 22 is autumnal (fall) equinox
for the Northern Hemisphere
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Remember the seasons are reversed south of the
Equator, so they have spring equinox on Sept 22 and
fall equinox on March 21
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Go here to see a cool demo for this
section

www.phschool.com and enter code cfp-5012
Essential Questions – Answered
1.
How does Earth move in space?
Earth rotates on its axis. Earth
also revolves around the Sun.
2.
What causes the cycle of seasons
on Earth?
Earth is tilted on its axis. This
tilt causes the Sun’s rays to
strike the Earth at different
angles at different times of year.