Earth, Moon, and Sun – Course 3 5-1 Earth in Space

Vocabulary Axis- An imaginary line that passes through a planet’s center and its north and south poles, about which the planet rotates. Rotation- The spinning motion of a planet on its axis. Revolution- The movement of an object around another object. Calendar- A system of organizing time that defines the beginning, length, and divisions of a year. Solstice- Either of the two days of the year on which the sun reaches its greatest distance north or south of the equator. Equinox- Either of the two days of the year on which neither hemisphere is tilted toward or away from the sun.

My Planet Diary pg. 182 The Seasons: Misconception: The seasons change because Earth’s distance from the sun changes. Fact: Seasons are the result of Earth’s tilted axis. Evidence: Earth’s distance from the sun does change, but that’s not why Earth has seasons. If that were the cause, people in the Northern and Southern hemispheres would have the same seasons at the same time. Instead, seasons in the Northern and Southern hemispheres are reversed. As Earth moves around the sun, sometimes the Northern Hemisphere is tilted toward the sun. At other times the Southern Hemisphere is tilted toward the sun. Why are summers generally warmer than winters? Why are the winters warmer in Florida than in Massachusetts?

rotation and revolution How Does Earth Move? Pg. 183 Until a few hundred years ago, most people thought that Earth stood still and the sun, moon, and stars moved around it. But today, Scientists know that Earth itself moves and that objects seem to move across the sky because of Earth’s motion. Earth moves in space in two major ways: rotation and revolution

Rotation pg. 183 Earth moves in space in two major ways: rotation and revolution. Rotation is the spinning of Earth on its axis. Earth’s axis is an imaginary line that passes through Earth’s center and the North and South poles. The rotation of Earth causes day and night. Draw an arrow to show the Direction In which the Earth rotates. Draw a line separating day from Night. Sequence- In which city will the Sun set next?__________________ Challenge- Where on Earth is it Noon? Midnight?________________ ______________________________

Revolution pg. 184 Revolution is the movement of one object around another. One revolution of Earth around the sun is one year. Earth’s path, or orbit, around the sun is an ellipse. The ellipse brings the planet closest to the sun in January. People of many cultures have used the motions of Earth and the moon to establish calendars.

Calendar pg. 184 A calendar is a system of organizing time that defines the beginning, length, and divisions of a year.

Assess Your Understanding pg. 185 1a. Identify- Earth’s ________________causes day and night. b. Explain- How does the sun’s gravitational attraction impact Earth’s motion? ____________________________________ ___________________________________________________ c. Infer- Why do people use Earth’s motions to determine units of time? ____________________________________________ I get it! Now I know that Earth moves by ___________________

How Sunlight Hits Earth Pg. 186 Near the equator, sunlight hits Earth’s surface from almost overhead. Near the poles, sunlight arrives at a steep angle. As a result, near the poles sunlight is spread out over a greater area. That’s why it is warmer near the equator than near the poles. INFER- DRAW A CIRCLE AROUND THE AREA WHERE SUNLIGHT IS MOST DIRECT. MARK AN X ON THE PLACES THAT SUNLIGHT REACHES, BUT WHERE IT IS LESS DIRECT.

Earth’s Tilted Axis pg. 186 If Earth’s axis were straight up and down relative to its orbit, temperatures in an area would remain fairly constant year-round. There would be no seasons. However, Earth’s axis is tilted at an angle of 23.5˚ from the vertical. So as Earth revolves around the sun, the north end of its axis is tilted away from the sun for part of the year and toward the sun for part of the year. Earth has seasons because its axis is tilted as it revolves around the sun. The diagram shows how Earth moves during the Year. It is not drawn to Scale. Compare the weather and Sunlight in the Northern And Southern hemisperes In March and September.

Solstices pg. 188 The sun appears farthest north or south of the equator twice each year. Each of these days is called a solstice. In the Northern Hemisphere, the summer solstice occurs around June 21. That is the longest day of the year in the Northern Hemisphere and the shortest day in the Southern Hemisphere. Similarly, around December 21, the winter solstice occurs in the Northern Hemisphere, while the summer solstice occurs in the Southern Hemisphere.

Equinoxes pg. 188 Halfway between the solstices, neither hemisphere is tilted toward the sun. Each of these days is called an equinox. On an equinox, the noon sun is directly overhead at the equator, rises due east, and sets due west.

Solstices and Equinoxes The diagrams show the apparent path of the sun at the solstices and equinoxes in the Northern Hemisphere. What is the sun’s path at the equinoxes and the December solstice for the Southern Hemisphere? Draw the sun’s Path at the Equinoxes And the Winter solstice For the Southern Hemisphere.

Do the Math! Calculating Percents The table shows the number of hours of sunlight in three cities at different times of year. What percentage of a 24-hour day has sunlight in Miami on January 1? Step 1- Divide the number of hours of sunlight by the total number of hours Step 2- Multiply by 100 to find the percent Calculate- What percentage Of a day has sunlight in Helsinki on July 1 ? ___________________________ 2. Calculate- What is the Difference in the percentage of The day that has sunlight in Helsinki and in Toronto on January 1? 3. Infer- What percentage of the Day would you expect to have Sunlight at the equator in January? In June?

Assess Your Understanding pg. 189 2a. Define- The noon sun is directly overhead at the equator during (a solstice/an equinox). b. What causes the seasons?_______________________________ __________________________________________________________________________________________________________ c. How would the seasons be different if Earth were not tilted on its axis? Explain. ________________________________________ I get it! Now I know that Earth’s seasons are caused by __________ ______________________________________________________