Experimenting with rotation, revolution and Earth's tilt on its axis.
GRADE - EXPLORING NIGHT/DAY AND SEASONS
The Solar System and all its planets are in constant motion. Each of the planets revolves around the Sun. The planets also rotate, or spin, around an internal axis. One manifestation of rotation is the cycle of night and day. Day after day, month after month, year after year, the alternation of night and day continues. Sometimes it is sunny outside, and other times it is dark. In addition to rotation, day and night occur because the Earth is spherical. When a portion of the Earth faces the Sun, it is daytime. When the same are rotates away from the Sun, it is nighttime. The cycle of light and dark is continuous except near the North and South Pole. During the Northern Hemisphere summer, the North Pole always faces the Sun, so daytime is continuous for several weeks. At the same time, the South Pole faces away from the Sun (Southern Hemisphere winter) and is in continuous night.
The origin of night and day is very difficult for children to understand. The idea that the dark side is really a shadow of the planet as it rotates away from the Sun’s rays is difficult to imagine. The rotation of the Earth on its axis, is also not easy to understand, because we cannot feel this motion.
Light rays from the Sun touch only the side of the Earth that is facing the Sun. While the Earth is spinning on its axis, it is also revolving around the Sun. The Earth is always rotating, spinning eastward. We do not sense this motion, however, because everything else on the Earth’s surface is moving as well. There is no independent frame of reference for observing rotation. Viewed from space, however, the Earth is clearly spinning. A point on Earth takes 24 hours to complete one rotation and come back to its starting point. The Earth spins completely once in 24 hours or in 1 day. The axis is the internal line around which the Earth rotates. The axis is tilted 23.5o from an imaginary vertical line drawn through the Earth.
Light rays from the Sun touch only the side of the Earth that is facing the Sun. While the Earth is spinning on its axis, it is also revolving around the Sun.
1. Last time we talked about what produced light in the sky (like … stars) and what reflects light in the sky (like the moon and the planets, etc.). Today we are going to put it together and talk about why we have day and night, a year and seasons.
First you need to know two words “rotate” and “revolve”. Rotate means to turn around on an axis. Imagine there is a stick going down my body and I turn around on it. That is rotating (demonstrate). Show them the globe rotating on its axis. Revolve means to go around something. Use the earth sun model to show the earth revolving around the sun. You can also demonstrate by calling a student up and going around them. So the earth is both rotating and revolving around the sun at the same time.To illustrate rotation and revolution, show students slide 4 of the Solar System and Beyond slideshow. Explain that the Earth rotates on its axis, but revolves around the Sun at the same time. Explain that night and day is caused by rotation, and that the seasons are caused by the tilt of the axis and the revolution around the Sun
2. Play the rotation and revolution song.
3. Have the students stand up, and rotate or spin. Make sure they understand that this is rotation.
4. Have students work in pairs. Have one student revolve around the other. Explain that this is revolution.
Tell the students that the Earth rotates as it revolves around the Sun.
Ask them to figure out what these motions will look like, using one pair
of students. Don’t let them do these activities for too long or else you
will have many dizzy students! (optional)
6. Explain why the Earth has night and day. Divide the students into groups
of two. Give each group a flashlight. Instruct them to think about
creating day and night. Have one student be the Sun by holding the
flashlight. The other student is the Earth (Earth Ball).
7. Ask the students to create day in the United States, then night. If one country is day, which country is in night? Go through as many locations as it takes for the students to understand the concept of day and night.
8. What causes day and night? The shadow from one side of the Earth. So the rotation of the earth is what causes …..(pause and let them answer)… day and night since one side gets the light and the other is in shadow. And the revolution of the earth around the sun causes ….. (a year).
9. What causes the seasons??? Turns out it is the tilt of the earth on its axis!
10. Play video Bill Nye and Seasons (this is just 4 minutes of a longer video but covers all important parts)
11. Use the earth sun model in the lab. When the northern hemisphere is pointed toward the sun, it is summer there and winter in the south. Then demonstrate the reverse. Then show fall and spring are in between. Tell them you now get to act out the seasons using a flashlight and a Styrofoam ball on a stick. Show them that if the northern hemisphere is pointed toward the sun is it summer in the northern hemisphere (and winter in the southern hemisphere). When the northern hemisphere is pointed away it is winter in the north and summer in the south. Call out seasons and have them position their sun and earth balls correctly.
12. Next, Stick a pushpin in the middle or the northern hemisphere (~ where we are) on the Styrofoam ball with the stick. Have one person use a flashlight and face it directly at the ball. Have them watch the shadows on the ball. When is the shadow shorter? (summer, when the axis is pointed toward the sun/flashlight). When is the shadow longer (winter, when the axis is pointed away from the sun/flashlight). How are the length of the shadows during spring and fall? (in between length).
13. Tell them this is what is happening in their measurements of the shadows in their long term project they have been doing in class. The shadows are longest in the winter when the northern hemisphere is pointed away from the sun and shorter when the northern hemisphere is pointed toward the sun. This is why the days are longest in summer but the shadows are the shortest and the days are shortest in winter but the shadows are the longest.
14. FINAL REVIEW (these can be phrased as questions)
Rotation of the earth causes day and night
Revolution around the sun is our year.
Earth’s tilt is why we have seasons.