Earth Science Lab: the Apparent Path of the Sun

Name: ______Period: ______

Earth Science Lab: The Apparent Path of the Sun

Directions: The purpose of this lab activity is to have you become familiar with the apparent path the sun takes across the celestial sphere. The apparent pathway of the sun across the celestial sphere is ever-changing depending on the latitude of the observer; time of day and the date the observation was made.

Introduction: View the photograph below, which is a composite image showing three positions of the Sun in the Southern sky at solar noon, for an observer in the Northern Hemisphere. At each of the Sun’s positions, a date has been provided. Answer the two questions that follow!

1. Make a hypothesis: why do you think the Sun has different altitudes at different times of the year?

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______2. During which date does the Sun “appear” to be larger in the sky? What might cause this apparent change in its size?

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______Procedure: Visit the website given below: http://astro.unl.edu/naap/motion3/animations/sunmotions.html

The website provides an interactive tool for visitors to manipulate in their understanding of apparent motions of the Sun. Before you begin, please be certain the following adjustments have been made to this tool:

1. Under ANIMATION CONTROLS, select “Loop Day” 2. Under GENERAL SETTINGS, select “Show the Sun’s Declination Circle”, “Show Stick Figure and its Shadow” and “Time of Day”.

Part I: Apparent Pathways of the Sun at Various Locations Throughout the Year:

1. Design the apparent pathways the Sun will take at each of the four locations represented by the celestial spheres shown. You will need to draw the apparent path of the Sun during the Summer Solstice, Winter Solstice and Vernal/Autumnal Equinox. Under TIME AND LOCATION CONTROLS adjust “the observer’s latitude” and “the day of the year” to obtain the correct pathways needed. 2. Remember the following dates for the seasonal events listed and use the color key provided to design your sun-paths on the five celestial spheres: a. Summer Solstice = June 21st ---(RED) b. Winter Solstice = December 21st ----(BLUE) c. Vernal/Autumnal Equinoxes = March 21st/September 23rd--- (GREEN)

Part III: The Celestial Sphere – 41˚N latitude (Long Island) Directions: Answer the questions below based on the diagram provided.

The diagram above represents the apparent path of the Sun at three different dates during the year for an observer at 42˚N latitude. The Sun’s paths are labeled I, II, III. The letters “A” through “I” are points on the paths. The numbers “1” through “4” represent compass directions.

1. What date is represented by each of the paths? Explain your answer! (Hint – Describe the path length and position of the Sun at sunrise/sunset)

a. Path I: ______

b. Path II: ______

c. Path III: ______

2. What is the cause of the apparent daily motion of the Sun along each one of the paths shown? ______

3. Which number represents north on the horizon? Explain your answer! ______

4. Which path represents a day where there are 12 hours of daylight and 12 hours of darkness and what are the possible dates for this sun path? ______

5. Which path will give the observer a minimum amount of solar energy? How do you know this? ______

6. Which letter represents the Sun at 3:00 pm on March 21st? ______

7. Which letter represents solar noon on June 21st? ______

8. As the Sun moves along “Path I” from A to B to C the length of the shadow cast by the observer will change. Explain how the shadow will change and why it will change? ______

9. Draw and label the Sun’s apparent path on the celestial sphere on Thanksgiving Day .

Part IV: Calculating the Altitude of Solar Noon Directions: An observer can calculate the altitude of the Sun at solar noon in the Northern hemisphere. During the Summer and Winter Solstices and both Equinoxes (Fall and Spring), an observer can calculate the Sun’s altitude at solar noon using the following equations:

***NOTE – The number 23.5 is an important value in the equation. This value accounts for the 23.5˚ tilt of Earth’s axis. This is significant when determining the altitude of the Sun at solar noon. If the angle of Earth’s tilt should change, the number 23.5 in the equation would change and be replaced by the new angle of Earth’s tilt. ***

1. Ralph is located at 33˚N latitude. What would be the altitude of the Sun at solar noon on September 23rd? ______

2. Denise is enjoying her cruise through the Caribbean Sea on June 21st. If she is located at 19˚N latitude what is the altitude of the Sun at solar noon? ______

3. What is the altitude of the Sun at solar noon during the Winter Solstice for an observer in Elmira, NY? ______

Part V: Conclusion

What if the tilt of the Earth changed? Scientists have reason to believe that the Earth has not always been tilted 23 ½ ˚. Different celestial events, such as the impact of a large asteroid with the Earth or the gravitational pull of a passing comet may cause a slight variance in the Earth’s tilt. What if there was a substantial change in the tilt of the Earth…perhaps a tilt of 40˚?

“How would the apparent path of the Sun across the New York sky change if the Earth were tilted 40˚?” 1. Calculate the altitude of the Sun at solar noon for New York City (41˚N) for the Summer and Winter Solstices should the Earth’s tilt be at 40˚ angle.

Be certain to use information from Part IV of this lab to assist you. Pay close attention to the NOTE. This information will assist you with your calculations. Show your work below:

a. Angle of the Sun at solar noon in New York City during the Summer Solstice with an Earth’s tilt of 40˚

b. Angle of the Sun at solar noon in New York City during the Winter Solstice with an Earth’s tilt of 40˚

2. Plot and draw your calculated Summer and Winter Solstices onto the celestial sphere provided. Be certain to use a RED colored pencil to show the Sun’s apparent path during the Summer Solstice and a BLUE colored pencil to show the Sun’s apparent path during the Winter Solstice. 3. Extension Question:

“What type of seasonal change would New Yorkers experience in the summer and winter if the Earth’s tilt had changed from 23.5˚ to 40˚? Use the celestial sphere diagram to help support your idea.”