5-1 Earth in Space

Earth, Moon, and Sun – Course 3

VocabularyAxis- 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. 182The 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.

1. Why are summers generally warmer than winters?

2. Why are the winters warmer in Florida than in Massachusetts?

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. 183Earth 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.

1. Sequence- In which city will the Sun set next?__________________

Challenge- Where on Earth is it Noon? Midnight?______________________________________________

Revolution pg. 184Revolution 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. 186Near 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. 186If 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 theYear. It is not drawn toScale.

Compare the weather andSunlight in the NorthernAnd Southern hemisperesIn March and September.

Solstices pg. 188The 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. 188Halfway 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 EquinoxesThe 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’sPath at the EquinoxesAnd the Winter solsticeFor the Southern Hemisphere.

Do the Math! Calculating PercentsThe 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

1. Calculate- What percentageOf a day has sunlight in Helsinki on July 1 ?___________________________

2. Calculate- What is the Difference in the percentage ofThe day that has sunlight in Helsinki and in Toronto on January 1?___________________________

3. Infer- What percentage of theDay would you expect to have Sunlight at the equator in January? In June?______________________________________________________

Assess Your Understanding pg. 1892a. 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 __________

______________________________________________________