# mgunter_177_3457866041

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```					Chapter 19, Section 1
Earth in Space
Wednesday, April 28, 2010
Pages 636 -- 643
Objectives
Identify the effects of Earth’s rotation and
revolution.
Explain the causes of the seasons on Earth.
Vocabulary Words
 Astronomy       Latitude
 Axis            Solstice
 Rotation        Equinox
 Revolution      Vernal equinox
 orbit           Autumnal equinox
Astronomy
Ancient Egyptians were among the first
people to study the stars.
They relied on the stars to predict the annual
flood.
They relied on the stars to plant their crops
Astronomy is the study of the moon, stars,
and other objects in space.
Rotation
 Earth’s axis is an
imaginary line that passes
through the Earth’s
center and the North and
QuickTime™ and a
South Poles.
decompressor
are neede d to see this picture.
 The North end points
toward Polaris
 The Earth spinning on its
axis is called rotation.
 Earth’s rotation on its axis
is what causes day and
night.
Revolution
the Earth also travels
around the sun.
QuickTime™ and a
decompressor
are need ed to see this picture.         The Earth’s movement
around the sun is
called a revolution.
 One complete
revolution around the
sun is called an orbit.
Earth’s orbit around the sun -- notice that the
orbit is not quite a circle -- it’s oval shape!
 The Egyptians were                    Calendars
one of the first
civilizations to use a
calendar.
 Egyptian astronomers
would count the
number of days                  QuickTime™ a nd a
decompressor
between each first       are need ed to see this picture.
appearance of the star
Sirius.
 They found that 365
passed between each
sighting
Calendar -- cont’d
 Earth’s orbit around
365 1/4 days.
 We view this as 3
years of 365 days and             QuickTime™ and a
decompressor

1 year of 366 days
are neede d to see this picture.

(leap year)
Seasons
 Most places have 4
distinct seasons.
 Winter
 Spring
 Summer
 Autumn (Fall)
QuickTime™ and a

 While there are 4               decompressor
are neede d to se e this picture.

distinct seasons, the
temperature will vary
depending on where
you live.
Seasons -- cont’d
 Earth has seasons
because its axis is
tilted as it moves
around the sun.

It’s warmer near the equator because sunlight
hits Earth’s surface at a direct angle. The sunlight
is spread out more in the other areas.
Earth in June
 In late June, the Earth’s axis is tilted toward the
sun.
 The hemisphere that’s tilted toward the sun has
more hours of daylight.
 The combination of direct sunlight and longer
hours gives us summer in the Northern
Hemisphere.
 At the same time, there is less sunlight and fewer
hours, giving us winter in the Southern
Hemisphere.
Earth in December
People in the Southern Hemisphere
receives the most sunlight giving them
summer.
indirect sunlight giving us winter.
Solstice
There are two days each year when the
noon sun is overhead at either 23.5 degrees
south or 23.5 degrees north.
These days are called solstice.
23.5 degrees south is called winter solstice
( around 12/21 is shortest day of the year)
and 23.5 degrees north is called summer
solstice (around June 21 is longest day of
the year).
Earth in March and
September
Halfway between the winter and summer
solstices, neither hemisphere is tilted
toward or away from the sun.
This happens on only two days each year.
The noon sun is directly overhead at the
equator.
These days are called equinox
Earth in March and
September -- cont’d
Vernal equinox is also known as spring
equinox and it’s usually on March 21.
The vernal equinox marks the beginning of
spring in the Northern Hemisphere.
Autumnal equinox is usually around
September 23 and marks the beginning of
fall in the Northern Hemisphere.
QuickTime™ and a
decompressor
are neede d to see this picture.
Review Questions
Explain the process that causes day and
night.
What two factors cause the cycle of the
seasons?
Compare rotation and revolution.
What is solstice? How does solstice relate
to the position of the Earth’s axis?
What is equinox? How does equinox relate
to the position of the Earth’s axis?
Homework
Workbook 19.1 (4/30)
Vocabulary quiz 19.1 (4/30)

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