# Chapter 3

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## Chapter 3

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1. Chapter 3 Section 1 Earth-Sun Relationships

2. Objectives • Explain the difference between climate and weather • Identify the significance of the Earth’s tilt, rotation, and revolution • Locate the Tropics of Cancer and Capricorn

3. Climate and Weather • Climate is often confused with weather, which is only one aspect of climate. • Weather is the condition of the atmosphere in one place during a limited period of time. • Climateis the term for the weather patterns that an area typically experiences over a long period of time.

4. Whether the climate in a particular region is cool and wet or hot and dry is determined by many factors, the most important of which is the earth’s position in relation to the sun. • The sun’s heat and light reach the earth as warmth and sunlight, but they reach it at different times and intensities.

5. Earth’s Tilt and Rotation • The earth’s tilt is one reason for variation in sunlight. • The earth’s axis, an imaginary line running from the North Pole to the South Pole through the planet’s center is currently tilted at an angle of about 23 ½ ⁰. • For this reason, the angle of tilt affects the temperature- the measure of how hot or cold a place is.

6. Temperature is usually measured indegrees on a set scale. The most common scales for measuring air temperature are Fahrenheit (⁰ F) or Celsius (⁰ C) • The Earth receiving light also depends on the side of the planet the sun is facing. • The Earth rotates every 24 hours. Rotating from west to east, the earth turns first one hemisphere then another towards the sun

7. Earth’s Revolution • While rotating on its axis, the earth travels in orbit around the sun, our nearest star. • It takes the earth a few hours more than 365 days- 1 year- to complete one revolution, or trip around the sun. • The seasons are reversed North and South of the equator. • Around March 21st, the sun’s rays fall directly on the Equator, this day is called an equinox because day and night times are equal.

8. Objectives • Explain the significance of the Poles • Analyze the importance of the Greenhouse Effect • Evaluate the different viewpoints of scientists regarding Global warming

9. The Tropics of Cancer and Capricorn • As the earth continues its revolution around the sun, it moves so that eventually the sun’s rays directly strike the latitude of 23 ½⁰ N- known as the Tropic of Cancer. • It hits the Tropic of Cancer about June 21st. • This gives the North the longest day of sunlight, known as the summer solstice. • By September 23 the sun hits the equator again, and marks the beginning of fall in the Northern Hemisphere.

10. As the sun’s rays go south, they reach their southernmost latitude, 23 ½⁰ S- The tropic of Capricorn- about December 22. • The winter solstice is the day of shortest daylight in the Northern Hemisphere. • This day is the beginning of winter.

11. The Poles • The amount of sunlight at the Poles varies as the earth’s revolution and tilt cause the changing seasons. • For six months of the year, one Pole is tilted towards the sun and receives constant sunlight while the other pole is tilted away. • At the North Pole, the sun never sets from about March 20 to September 23. • At the South Pole daylight is from September 23 to March 20th.

12. The tilt of the earth’s axis causes this natural phenomenon, known as midnight sun. • Parts of North America (including Alaska) and northern Europe in the Arctic have become popular tourist destinations because of this.

13. The Greenhouse Effect • The Earth’s atmosphere is like the glass in a greenhouse. • It traps the sun’s warmth for growing plants even in cold weather. • Without this greenhouse effect, the earth would be too cold for most living things. (Page 70) • The 50% of the sun’s radiation that reaches the earth is converted into infrared radiation, or heat.

14. Clouds and greenhouse gases such as water vapor and carbon dioxide (CO₂) absorbs the heat reflected by the earth and radiate it back again so that a balance is created. • Many scientists claim that in recent decades there has been a rise in atmospheric CO₂. • This has coincided with rising temperatures. This trend is known as global warming.

15. Global warming is believed to be a part of human activities. • Using computer models, some scientists predict that global warming will make weather patterns more extreme. • Scientists do not all agree on global warming and its effects. Some say it is a natural cycle, others say the evidence is inconclusive.

16. Discussion • What did you learn today?

17. Assessment • Page 58 1-6