# Charting Seasonal Changes

### Purpose:

To explore data related to the daily, monthly and yearly cycles of  the earth, moon, and sun.   To  create a variety of charts and graphs and evaluate different methods of  presenting numeric data.

### Overview:

Students will research the Earth's patterns of rotation and revolution, create a charts and graphs  of these patterns and use them to explain the causes of night and day and  summer and winter. The different graphical formats will be compared and evaluated.  The project can be extended to data on the phases of the moon and tides.

### Topics:

Scientific Visualization:
Earth Science (Astronomy):

### NC Scientific and Technical Visualization Objectives:

#### Level I:

2.00     Apply problem solving and design concepts.
4.01     Identify and explain the application of description systems for space and time.
4.04     Describe visual methods for representing data driven visualizations.
5.01     Design and evaluate a simple visualization.
5.03     Produce computer based data driven visualization projects.

### NC Earth and Environmental Science Goals and Objectives (1999 Revision)

6.02    Analyze planetary motion and the physical laws that explain that motion:

• Rotation
• Revolution
• Apparent diurnal motions of the sun and stars.
• Tilt of the earth's axis.
• Parallelism of the earth's axis.

### Tools

Research - Internet access is best but sample data for Raleigh, North Carolina and Santiago Chile is provided for those classes without internet access.
2D charts - Excel  or other spreadsheet

### Teacher Information

It is essential for teachers to realize that many people have serious misconceptions about the causes of phenomena such as seasons, lunar phases, tides, eclipses etc. For example,  a common misconception is that the earth is further from the sun in winter than in summer. (In fact the Earth is closest to the sun in December which is winter in the Northern hemispere.)  Research shows that these misconceptions are held even by many college graduates so do not expect your students to understand these phenomena without assistance!  These misconceptions sometimes arise from a combining personal experience with poorly understood previous instruction and  misinterpretation of pictorial drawings in Earth Science textbooks. These misconceptions  powerfully shape student  understanding of new material including diagrams, videos and teacher explanations.  Asking students to create their own visualizations can help the students overcome previous misconceptions and come to a more scientific understanding of phenomena.  Before beginning this project, teachers should be sure students have a basic understanding of the Earth's daily  and yearly cycles.  This can be accomplished by having students create  a 3D animation as outlined in  the Earth in Space lesson (link coming soon!) or by simulating this with a lamp and a globe in the classroom.  The teacher's role is to ask probing questions challenging misconceptions.  This is an essential role - otherwise the student may create a visualization that reinforces a misconception.   Question students carefully to be sure they understand before proceeding to work with numerical data!!! Some links to material about misconceptions are given below in the reference section.

Here is a sample of a type of graph students could make to compare daylength in three locations:

Students should be able to use this type of graph to discuss questions such as: When does Santiago, Chile have its shortest days? Which place experiences the shortest days?  Which place experiences the longest days? When do all three places have days that are about the same length?  Which place experiences the greatest change in daylength over the course of the year?  They should relate this to their 3D visualizations to explain why Chile is having its longest days when Raleigh's days are at their shortest and why Bangor has greater changes in daylength than Raleigh or Santiago.  The teacher or students can choose different locations of interest and the teacher might adjust the questions accordingly.

The sun's (or other heavenly body's) apparent position at any time can be given with two coordinates, it's altitude  and azimuth. To help students develop their understanding of these coordinates and the relation of the apparent position of the sun to the Earth's movements do the Altitude Azimuth Activity  (coming soon) before  graphing altitude and azimuth.

Altitude is the angle up from the horizon. Zero degrees altitude means exactly on your local horizon, and 90 degrees is "straight up".  A negative altitude indicates  that the center of the sun is below the horizon as in before sunrise or after sunset .  Azimuth is the degrees East of North along the horizon.  Thus when the sun is  rising due east,  the azimuth at sunrise is 90 degrees.  In the northern hemisphere the azimuth at sunrise will be greater than 90 in the winter and less than 90 in the summer.    The altitude and azimuth values given at the Naval Observatory site are for the center of the apparent disk of the Sun or Moon. The altitude values include the effect of  standard atmospheric refraction when the object is above the horizon. The azimuth values are computed with respect to true north (not  magnetic). For locations in the U.S.  times in the tables are given in standard local times,  not daylight savings times.  For locations outside the U.S. conversions from Greenwich Mean Time (Universal Time) must be entered.

Here is a sample Altitude Azimuth graph for Raleigh in 1999:  (Note:  there are many different effective ways to present this data.)

Close observation of the times of sunrise and sunset over the course of the year will reveal some interesting patterns beyond the obvious days longer in summer shorter in winter.   If your students wish to explore the reasons for this, direct them to search for information on the "equation of time."  Some good websites for this are listed below in the reference section.

This project offers a good scope of interesting data to analyze and present.   Although some data is provided here it will be much better for students to go to the web sites and download the data themselves if  web access is provided at your school.   A wide variety of  astronomical data is available from the U.S. Naval observatory at http://aa.usno.navy.mil/AA/ .  Importing and formatting this data into Excel is somewhat time consuming  but a useful exercise in developing understanding of data types.   We have provided step by step instructions for downloading this data,  formatting it in Excel, and creating charts.

This project can be assigned to individuals or groups of students.  It can easily be extended to a much more difficult level but it is important to be sure all students understand the basic concepts first.     Related topics which could be done by other groups or included in a large project include the relative sizes and distances of  the sun, planets, and moons in the solar system,  eclipses, Kepler's laws of planetary motion, precession of the earth's axis, etc.

Links to sample data for 1999:

• Sunrise and sunset in Raleigh, North Carolina, U.S.A.
• Azimuth at sunrise in Raleigh, North Carolina, U.S.A.
• Sunrise and sunset times in Santiago, Chile
• Azimuth at sunrise in Santiago, Chile

•

Some interesting questions to ask are below in the discussion questions section.  Students should figure out what data and graphs they need to answer their assigned question(s). Students will need time zone conversions and latitude and longitude, both of which are available as links from the Naval Observatory or in any good atlas.   With each question students should be asked to design a 2D graph to communicate these patterns to others.  Then they need to incorporate these graphs into a presentation which explains the patterns.   After everyone presents their projects the teacher should ask the students which charts and graphs conveyed which patterns most effectively and why.

#### Discussion Questions (for graphs)

 1 How does  the time and position of sunrise change during the year? What patterns can you observe? 2 What patterns does the amount of change from day to day follow? 3 How is Fall with the days getting shorter different from just the reverse of Winter when the days are getting longer? 4 How do these patterns vary in different places?  Different groups can make charts for different place so that comparisons from East to West  in one time zone (e.g. Wilmington to Asheville), from North to South in the Northern Hemisphere (e.g. North Carolina or further south  to Maine or further north), and from Northern to Southern Hemisphere are possible. 5 How does day length change from day to day?  Compare also the amount of change in the time of sunrise from one day to the next at different times of the year  and with the amount of change in the time of sunset. 6 How does the path that the sun takes through the sky different in summer and winter?  Graph Time and Azimuth at intervals throughout the day. 7 Compare the graph for question 6 for a North Carolina location  for June 21 and December 21 with other locations for those same days.

### Student Assignment Sheets

#### 2D Data Driven Visualization

Your group will be assigned to use the web to find data to answer one or more of the following questions.  A good web site to use is provided by the U.S. Naval Observatory at  http://aa.usno.navy.mil/AA/ .    After you find the data you will need to transfer it to Excel and then create charts that clearly show the patterns in the data.   If several charts are to be created in order to compare data for different times and places be sure that the choice of axis and scale allows for easy comparison between graphs.  Use your charts to explain what you found to your classmates.    You should also be able to explain the reasons for these patterns based on the Earth's patterns of movement around the sun.

 1 How does  the time and position of sunrise change during the year? This will require getting the times of sunrises and then finding the azimuth at that time for each day.  You might choose to find data for certain days such as the first and 15th of every month.  Then you will need to chart this data.  What patterns can you observe?. 2 What patterns do the amount of change from day to day follow? (For example is sunset one minute later each day in Spring or is there a more complicated pattern?) 3 How is Fall with the days getting shorter different from just the reverse of Winter when the days are getting longer? 4 How do these patterns vary in different places?  Different groups can make charts for different place so that comparisons from East to West  in one time zone (e.g. Wilmington to Asheville), from North to South in the Northern Hemisphere (e.g. North Carolina or further south  to Maine or further north), and from Northern to Southern Hemisphere are possible.  If the same scale is used the different graphs can be overlaid for comparison. 5 How does day length change from day to day?  Compare also the amount of change in the time of sunrise from one day to the next  in different places at different times of the year  and with the amount of change in the time of sunset. 6 How does the path that the sun takes through the sky differ in different places and in different seasons?   Graph altitude and azimuth at intervals throughout the day.  Overlay or combine with graphs from different times of  the year and from different locations.

### Evaluation Criteria:

Success will be measured by the following criteria:

 Find appropriate data to answer the question 5 Transfer the data to a spreadsheet 5 Create chart from data 5 Appropriate choice of chart type 5 Fonts chosen are clear and easy to read 5 Graphic has appropriate title 5 X and Y axes labeled clearly 10 Axes scaled to data 5 Grid lines aid graph clarity 5 Legends labeled clearly 5 Colors chosen to aid understanding 5 Data marks clear 5 Overall graph portrays pattern of data 10 Clear explanation of  reasons for pattern of data 20 Cooperation allows multiple graphs to be compared 5 Total 100

### Extensions:

Possible extensions include making charts and graphs of lunar and tidal data and showing how the moon's position affects tides,  presenting this to Earth Science classes or a younger audience, producing a CD ROM for other classes to use, or developing a class web site on  the Earth's motion in space.

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