Changing distance between the earth and the sun causes seasonal changes
(With the two closer in summer and farther apart in winter.)
Truth-
Seasons change on earth throughout the year due to the amount of direct sunlight that the hemispheres are receiving. The earth has a 23.5-degree tilt on its axis towards the North Star. When the Northern hemisphere is receiving more direct sunlight, it is summer in the Northern Hemisphere. At this same time, it is winter for the Southern hemisphere. As the earth revolves around the sun, the direct sunlight shifts, therefore changing the seasons in both northern and southern hemispheres.
Benchmark-
Area- Earth Science
Category- Solar System, Galaxy, and Universe
Benchmarks-
-Elementary #1: Compare and contrast characteristics of the sun, moon, and the earth.
Key concepts: planets, star, sphere, solar system, heat, light.
-Elementary #2: Describe the motion of the each around the sun and the moon around the earth.
Key Concepts: Spin, orbit, length of day, nighttime, month, year, observed movement of the sun and stats across the sky.
- Middle School #2: Describe, compare, and explain the motions of solar system objects. Key Concepts: Orbit, rotation (spin), axis, gravity, seasons. Tilt of the earth on its axis, direct/indirect rays.
Activity: (as taken from SME class)
Materials:
- Masking tape
- A light source (light bulb)
- 1 large Styrofoam ball
- 1 small rubber band
- 1 skinny stick (cabob stick)
- 2 push pins
- post it notes
- Construction paper
Directions:
Set Up
1. Set up the light source in the middle of a table. This will be the sun in the model.
2. Use the masking tape to create an “orbit” around the sun. Tape the masking tape to the table around the “sun”. The orbit should be round, but does not have to be perfect.
3. Place the rubber band around the Styrofoam ball in the center. This will be the equator on the earth
4. Stick the cabob stick into the “earth” so that the equator is horizontal.
5. Stick one push pin approximately where
6. Cut out a picture of a star that will serve as the North Star in this activity. It will be places on the wall, so that the earth will have a reference point for its axis tilt.
Activity
1. Turn on the “Sun”.
2. Take the earth that has been created and tilt the axis (the cabob stick) towards the North Star at approximately 23.5 degrees.
3. In a counter clockwise direction following the masking tape orbit, observe what happens to the sunlight as the earth revolves around the sun. (remembering always to keep the axis always pointed at the North Star)
4. Then, observe the Southern Hemisphere’s seasons at the pin, at the Northern Hemisphere pin’s first days of seasons and observe the amount of daylight each hemisphere receives at each of the first days of the seasons.
Results:
1. You will visually observe the same amount of sunlight is always striking the earth, but the sunlight strikes different parts of the earth at different times during the year.
2. You will also see that in the Northern Hemisphere, when the sun is most direct, that is summer. The number of sun hours per day is also at a maximum for the year.
3. You see that in the Northern Hemisphere, when the sun is least direct, that is winter. In this season, the hemisphere gets the least amount of sunlight hours.
4. You will observe that the seasons of Spring and Fall each receive the same directness of sunlight and both have about 12 hours per day and 12 hours per night.
5. Also you will notice that the Southern Hemisphere’s seasons are exactly opposite from the Northern Hemisphere. When the North is experiencing summer, the southern is experiencing winter. And when the Southern is experiencing spring, the northern is experiencing fall. This is true for all four seasons.
Explanation:
The activity shows a variety of information necessary to understanding the misconception that seasons happen because of the distance away from the sun. First, the orbit around the table in the activity shows that although earth’s orbit around the sun is not a perfect circle, there is barely any change in distance. There is most definitely not enough change in distance throughout the year to change the seasons on earth. Then the activity shows just how and why the seasons progress through the year. As the earth revolves around the sun, the axis always remains facing the North Star at a 23.5 degree angle. This tilt is what changes the directness of sunlight on the hemispheres. When the Northern Hemisphere tilts towards the sun, it is the season of summer. At this exact time, the Southern hemisphere is experiencing winter, because its half of the earth is not receiving direct sunlight, and the south has short days. As the Styrofoam ball moves around the orbit around the sun, with its axis tilted at the North Star, it is easy to observe summer (lots of direct sunlight), winter (little direct sunlight), and both Fall and Spring. On the Styrofoam ball, spring and fall happen when there is equal amounts of direct sunlight on both the northern and the southern hemisphere. This activity with the Styrofoam ball shows exactly how the sunlight is more direct during the summer and less direct in the winter. It also very accurately shows the opposite relationship of seasons in the Northern Hemisphere and the Southern Hemisphere. The directness of sunlight is the reason that the seasons change.
It is crucial to understand the tilt of the earth at its axis to understand how the seasons happen. If the earth did not have this 23.5 degree tilt, the earth would have no seasons. Every place on earth would always have one season, all the time. This tilt gives the earth the wobble-like movement that changes the seasons. As the earth revolves around the sun in a counterclockwise fashion, the wobbling of the earth happens at different times of the year, but they happen exactly the same time every year. The Southern hemisphere and the Northern hemisphere have the same seasons, only opposite one another. For example, when it is summer in the north, it is winter in the south. When the Northern hemisphere is pointed more directly toward the sun, it is obvious that the Southern Hemisphere is not. In the Northern hemisphere, it is summer when the earth has revolved so the tilt will give the north more direct sunlight. The hour of sunlight is about 15 hours. In the winter, sun appears to move down in the sky, and there is less direct sunlight. In the winter, there is only about 9 hours of sunlight. In spring, the sun light begins to be more direct, and the hours of light increase to about 12 hours. The sunlight continues to be more direct, and it becomes summer. The sunlight then becomes less direct, and the season becomes fall. Fall has about 12 hours of sunlight. The seasons do not just happen on the first days. It is a gradual process of the directness of sunlight moving from north to south and back up to the north. When the Northern hemisphere begins to lose direct sunlight, at the same time, the Southern hemisphere is gaining that directness of sunlight. The full cycle takes a year, which is how long it takes the earth to travel around the sun in its orbit.
Real World Examples-
EARTH-A real world example of the seasons changing is watching a deciduous tree during a one-year period. In the summer, the tree has green leaves and it very healthy and alive. The tree is getting a large amount of sunlight, because the sunlight is more direct, and the hours of sunlight is about 15 hours. The tree is also healthy because of all the rain that the tree has received. Rain was made possible as the Northern Hemisphere warmed up from the more direct sunlight as the earth revolves around the sun. As the earth continues to revolve, it becomes fall. The Northern hemisphere and the Southern Hemisphere receive the same amount of sunlight, and both hemispheres get the same amount of direct sunlight. The tree’s leaves begin to turn brown and red. The Northern Hemisphere is beginning to cool, and the tree is not as healthy as it was during the summer. As winter comes, the tree loses all of its leaves, and appears to have died. The cold and lack of sunlight forces the tree to lose its leaves, and stay that way throughout the winter. As the earth revolves, the Northern Hemisphere begins to turn towards the sun. The hours of sunlight increases, and so does the directness of that sunlight. The temperature starts to warm up, and instead of snow, the precipitation is rain. This rain helps replenish the tree. The tree begins to bud with leaves. These buds will continue to grow throughout spring into summer. Then the cycle of the tree repeats itself, just as the progression of seasons repeats its cycle.
MOON- Another real life example that I could never explain before was the idea of a new moon. I could never grasp why we could not see any part of the moon at all. I now understand that this is because the moon is always half lit by the sun. And when a new moon is taking place, the moon is in-between the earth and the sun, and we are seeing the un-lit side of the moon. So the sun is actually seeing the lit side of the moon.
PLANETS & STARS- A third real life explanation is the idea of constellations and signs being related to each month. This is because these stars make up a constellation that appears to look like some kind of design in the sky. These designs are not however in the night sky during that month, they are in the day sky. So for instance, a Capricorn (January baby) sees their constellation in July. Likewise for July, it sees its sign in the night sky in January. Before this lesson I have never understood that.
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