Seasons Lab

From GeoClasses

The Reasons for the Seasons

Question

Why do we have seasons?

Survey

• Fill out the initial survey. You should be able to answer these questions better when you are done with this lab.

Elipticity

Animation of an elliptical orbit. The ellipticity here is 0.5.

Observations

• The Earth's orbit is elliptical, therefore the distance between the Earth and the Sun changes over the course of a year.
  • Apheilion is when the planet is furthest from the sun, while perihelion occurs when the planet is closest to the Sun.
  • Pictures of the Sun at perihelion and aphelion show the slight difference that can be seen in the size of the Sun as the Earth moves further away from th Sun.
• The further away you move from the Sun, the less solar radiation you receive.

Showing aphelion and prihelion. The ellipticity is 0.3.

Hypothesis

The seasons are caused by the ellipticity of the Earth's orbit.

Testing

• Prediction - When the Earth is closer to the Sun the Earth receives more/less solar radiation so the Earth should experience summer/winter.
  • Observation - When is the Earth at its perihelion?

The earth is at its perihilion on June 21st which is the day that it is closest to the sun.

• Prediction - Based on the hypothesis, when the Northern Hemisphere has its summer, the southern hemisphere should have its summer/winter.
  • Observation - What season is it in the southern hemisphere when it is winter in the northern hemisphere?

When it is winter in the northern hemisphere is it summer in the southern hemisphere. This is so because each point is at the exactr oppostie of the other point. Each place experinces the extreme opposite of the other place.

Conclusion

Would you accept, reject or modify the hypothesis? ________________

Explain why.

I would except this hypothesis because it just makes scientific sense. If the north an the south hemisphere at the exacr opposite place place of each other then it only makes sense that they experice the exact opposite things. 

Axial tilt

Observations

• The two hemispheres experience the opposite seasons. For example, when it is summer in the Northern Hemisphere it is winter in the south.
• The Earth's axis is tilted relative to the plane of the ecliptic by 23.5 degrees.
• Thoughout the entire orbit of the Earth around the Sun the axial tilt remains the same. The fact that the axial tilt does not change is referred to as axial parallelism.
  • Movie showing the tilt of the Earth's axis and axial parallelism.

What does the word parallelism refer to?

Parallism refers to the imaginary line that the earth revolves around throughout each year. The earth stays aligned at the same place. 

Axial parallelism. The Earth is shown at the solstices.

• The solstices are the times when the Earth's axis is pointed most directly away from or toward the Sun, therefore there are two solstices every year. The winter solstice in the northern hemisphere (which is the summer solstice in the southern hemisphere) occurs on December 21 or December 22 every year, while the summer solstice (for the northern hemisphere) occurs on June 21/June 22.
  • The winter solstice is the shortest day of the year, and the summer solstice the longest.

The axial parallelism animation shows two images of the Earth. The image of the Earth on the left in the picture shows which solstice?

The image on the left shows the earth at its summer solstice.

• The equinoxes occur when the Earth is half-way between the solstices in its orbit around the Sun. At the equinox almost all regions of the Earth experience 12 hours of daylight and 12 hours of night.
  • This

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When do the equinoxes occur? (Show your calculations. No Googling it.) (Hint: consider when the solstices occur.)

Fall and the spring
The fall equinox which occurs on or around September 22nd occurs about half way in between the winter solstice and the summer solstice and the spring equinox occurs on or around March 20 occurs about half way in between the winter solstice and the summer solstice. 

 

Hypothesis

Because of axial parallelism, different parts of the Earth receive differing amounts of sunlight at different times of the year. When one part of the Earth receives more sunlight, it will be summer in that area. Therefore, axial parallelism is responsible for the seasons.

Testing

• Prediction - When the northern hemisphere is most directly facing the Sun it will be the warmest time of the year in the northern hemisphere and coldest in the southern hemisphere.

• Observations

When (on what date) is the northern hemisphere most oriented toward the Sun?

The Northern Hemisphere is most oriented towards the sun during the summer solstice.

When (on what date/month) is it warmest in the northern hemisphere?

The warmest date in the Northern Hemisphere is June 21st.

Conclusion

Would you accept, reject or modify the hypothesis? ________________

Explain why.

I would except the hypothesis for the same reasons stated above. First and formost it makes scientific sense. Because the North and South are at extreme place on earth they must experice very different things. And because of that each place recieves 6 months of darkness and 6 months of light. 

Past climate change

In the past, the Earth's climate has been significantly warmer and cooler than it is today. At the last glacial maximum (18,000 years ago) ice sheets covered much of North America.

Image of the Earth at the last glacial maximum. In this image you can see the maximum extent of the North American Ice Sheet. Image from Scotese, C.R., 2002, http://www.scotese.com, (PALEOMAP website).

Currently the best theory to explain these climatic fluctuations is the Milankovitch theory or orbital cycles. While inprisoned in an internment camp during World War I, Milankovitch used careful astronomical observations to predict changes in the Earth's orbit over 10's and 100's of thousands of years. He used this information to calculate the changes in solar insolation at the surface of the Earth over time.

Milankovitch observed changes in;

1. The ellipticity of the Earth's orbit
2. The axial tilt of the orbit
3. The orientation of the Earth's axis (and the precession of the equinoxes relative to perihelion and aphelion).

Questions

1a. If the ellipticity of the Earth's orbit increased, how would that affect the length and intensity of the seasons?. Be sure to explain your reasoning.

If the ellipticity of the Earth's orbit increased the seasons lenght and intensity would be effected gradually bit greatly. It would take a large amount of years to detect or to see the change but the seasons would become shorter and much more intense. It the earth speeds up on its orbit then each hemisphere would there seasons much quicker and go through much more quickly. 

1b. Would the amount of solar radiation received by the Earth in one year increase or decrease with a change in the ellipticity of the Earth's orbit. (Hint: Using the Ellipticity model might help.) Be sure to explain your reasoning.

The amount of soloar radiation would incerease because if some goes towards something faster and quicker the heat would increase and if the earth circle around the sun more quickly the intensity of the heat would definitely increase.

2a. How would an increase in the axial tilt of the Earth affect the length and intensity of the seasons? Be sure to explain your answer.

2b. How would an increase in the axial tilt of the Earth affect the total annual insolation reaching the Earth? Be sure to explain your answer.

3a. If the summer solstice in the Northern hemisphere were to occur at aphelion, how would the length and intensity of the seasons differ from the current condition where the summer solstice occurs close to perihelion.

3b. If the summer solstice in the Northern hemisphere were to occur at aphelion, how would total solar radiation received by the Earth (in a year) change?

Making a movie about the seasons

Create a movie explaining why we have seasons. Create the movie that you would like to have seen explaining the seasons.

Rules

1. Your final movie must have at least 12 clips. (Yes you can delete some of the original clips). If you wish to use less clips get permission from you instructor.
2. All clips must have at least one line of captions.
3. In your movie you must use the following terms at least once. (It may help to cross off the term after you've used it once):
   • Apheilion
   • Perihelion
   • Ellipticity
   • Summer
   • Winter
   • Axial tilt
   • axial parallelism
   • solstice
   • equinoxes
   • insolation
4. Bonus: if you can also explain why the Earth has had ice ages in the past.

Instructions

1. Log in to the MovieClassroom
2. Go to the bottom of your newly created homepage and click on the "BROWSE MOVIE CATALOG" button.
3. Find the movie titled "Seasons Lab" and press its "IMPORT" button.
   • This will take you back to the homepage.
4. On the homepage enter your name in <enter description here. text box, click the "UPDATE DESCRIPTION" button, and then click the "EDIT MOVIE" botton.
   • This will take you to the movie page which has all the video clips in the movie.
5. Rearrange the clips and enter captions for all the video clips to create a movie explaining why we have seasons.
   • Hit the EDIT SUBTITLES button every time you enter a caption, otherwise you might loose what you have entered.
   • When you are done press the "CREATE MOVIE" button to create a movie that will look something like the

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1. • Be sure to hit the Enter key after every two lines of captions, otherwise the captions will run off the page in the movie.
   • If you want to see what each clip looks like with the captions, hit the "EDIT SUBTITLES" button then click on the thumbnail image to see the clip.
2. SUBMIT the movie to your instructor by entering your instructor's USERNAME in the "SEND TO USERNAME" area.
3. OPTIONAL: If you would like, you can "PUBLISH" your movie. If you do then you are allowing anyone to see (and edit) it on the internet.

Lab Evaluation

1. Please answer these questions to help us improve this lab in the future.
2. See if you actually can give better answers on the initial survey you took at the beginning of this lab.