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Chapter 19, Section 1 Earth in Space Wednesday, April 28, 2010 Pages 636 -- 643.

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Presentation on theme: "Chapter 19, Section 1 Earth in Space Wednesday, April 28, 2010 Pages 636 -- 643."— Presentation transcript:

1 Chapter 19, Section 1 Earth in Space Wednesday, April 28, 2010 Pages 636 -- 643

2 Objectives  Identify the effects of Earth’s rotation and revolution.  Explain the causes of the seasons on Earth.

3 Vocabulary Words  Astronomy  Axis  Rotation  Revolution  orbit  Latitude  Solstice  Equinox  Vernal equinox  Autumnal equinox

4 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.

5 Rotation  Earth’s axis is an imaginary line that passes through the Earth’s center and the North and South Poles.  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.

6 Revolution  In addition to rotation, the Earth also travels around the sun.  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!

7 Calendars  The Egyptians were one of the first civilizations to use a calendar.  Egyptian astronomers would count the number of days between each first appearance of the star Sirius.  They found that 365 passed between each sighting

8 Calendar -- cont’d  Earth’s orbit around the sun takes about 365 1/4 days.  We view this as 3 years of 365 days and 1 year of 366 days (leap year)

9 Seasons  Most places have 4 distinct seasons.  Winter  Spring  Summer  Autumn (Fall)  While there are 4 distinct seasons, the temperature will vary depending on where you live.

10 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.

11 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.

12 Earth in December  People in the Southern Hemisphere receives the most sunlight giving them summer.  The Northern Hemisphere will receive indirect sunlight giving us winter.

13 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).

14 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

15 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.

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17 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?

18 Homework  Workbook 19.1 (4/30)  Vocabulary quiz 19.1 (4/30)

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