Calculating Photoperiods (Lengths of Days)

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SWBAT calculate the length of a day by looking up the sunrise and sunset times, recording the data and graphing the data.

Big Idea

The length of a day or photoperiod, changes depending on the time of year. Students will look for patterns in these changes and understand why these changes occur.

Lesson Overview-5 E Lesson Planning

5 minutes

Unit 2:Sun-Earth Connection (Solar System)

Lesson 5: Calculating Photoperiods

5E Lesson Planning:

I plan most of my science lessons using the BSCS 5E Lesson Model: Engage, Explore, Explain, Elaborate, and Evaluate.For a quick overview of the model, take a look at this video.

I use this lesson model because it peaks the students' interest in the beginning during the "Engage" portion and allows for the students to actively participate in the investigations throughout the subsequent steps. The “Evaluate” component of the 5E Lesson Model can be used in many ways by the teacher and by the students.

A great resource for lesson plan frameworks and explanations is the Community Resources for Science. The 5E Lesson Planning Template and 5E Lesson Planning Prompts come from this website. 

Unit Overview:

In this Unit students will learn about the solar system by studying the sun, the moon, planets and stars. In the first three lessons the students will learn about the Sun. Lessons 4 through 7 focus on the movement of the Earth around the Sun. Lessons 8 is lesson about Orreries, lessons 9 and 10 cover solar eclipses, lessons 11 and 12 are about the moon, lesson 13 discusses the other planets in the Solar System, and the last 3 lessons; 14-16 are about stars and constellations.  

Lesson Overview:

In this lesson, students will collect and graph data about Photoperiods- lengths of days,  to look for patterns and changes related to how long we have daylight. I decided to use data that has already been collected for the students to practice their calculations and then we will collect data over several weeks to look for patterns.

The materials needed for this lesson are:

  • handouts of data
  • recording sheet to collect new data
  • graph paper 
  • class graph
  • pencils
  • colored pencils
  • markers for class graph

 Next Generation Science Standards:

This lesson focuses on NGSS Standard 5-ESS1-2- Represent data in graphical displays to reveal patterns of daily changes in length and direction of shadows, day and night, and the seasonal appearance of some stars in the night sky.

The Disciplinary Core Ideas and Crosscutting Concepts of the NGSS that this lesson covers are described below. 

Disciplinary Core Ideas: This lesson aligns to the Disciplinary Core Idea from the Earth and Space Science:

ESS1.B: Earth and the Solar System. The Earth’s orbit and rotation,and the orbit of the moonaround the Earth cause observable patterns.

Crosscutting Concepts:


Similarities and differences in patterns can be used to sort, classify, communicate and analyze simple rates of change for natural phenomena. (5-ESS1-2) 

Analyzing and Interpreting Data

Analyzing data in 3-5 builds on K-2 experiences and progresses to introducing quantitative approaches to collecting data and conducting multiple trials of qualitative observations. When possible and feasible, digital tools should be used.

  • Represent data in graphical displays (bar graphs, pictographs and/or pie charts) to reveal patterns that indicate relationships. (5-ESS1-2)


10 minutes

After we have learned about What Makes Day and Night?, I ask the students how long they think the Sun is up during the day? I tell them to make a best guess or prediction and have them write this in their Science Notebook. 

I tell the students to share their guesses with their Science Group in a Round Robin for about one minute. I use the Round Robin cooperative learning strategy for several reasons. First, it gets the students talking about a concept we are learning. Some students tend to sit back and not participate in discussions during a whole group discussion, but they are usually more comfortable talking in a smaller group.

I then ask the groups to share what they think their best guesses are and I record these on the board. I then explain that we are going to learn about calculating the length of a day or photoperiod. I talk to the students about how scientists use the term photoperiod to determine how much sunlight a plant or animal needs and that patterns of migration for most animals is based on this. I remind the students that using the language that a scientist uses is using what is called "Language of the Discipline" which is one of the  Depth and Complexity Prompts developed by Dr. Sandra Kaplan from USC. I show the students the prompt and we discuss the meaning of photoperiod. 

I then pose the Big Idea to them (or Big Question) and have them write it in their Science Notebooks.

Why would scientists want to know about a photoperiod or how much sunlight there is in a day? Why would this be important? 



30 minutes

Before we start looking up and recording our own data, I have the students practice calculating photoperiods. I give them a handout that has data from another project called the "Mystery Class" that gives sunrise and sunset data from 2009. This is the Practice Packet and I give the students pages 3 and 4 from the packet to practice the calculations. This resource comes from the Annenberg Foundation and from a program called "Journey North".

I tell them that we will first figure out the best way to calculate the photoperiod for each of these days and that it would be best to change the times to "military time" or by using the 24 hour clock. Several students don't understand what a 24 hour clock means so I draw an example on the board and explain it to them. 

I model how to calculate the first few days for the students and then check to see if there's any challenges for them. I give them 10 minutes to finish the calculations. Here are students working on calculations and students calculating photoperiods

Next, I show the students how to look up the sunrise and sunset times for our city by going to this website. I do this during a class time in the computer lab so that all of the students can practice using this website and recording the data. We use this same website to look up the phases of the moon so this lesson can be done in conjunction with the Moon Observations lesson.


15 minutes

The next part of the investigation is done over the next few months (or it can be done throughout the school year). I explain to the students that we are now going to collect sunrise and sunset data for the next three months (or longer) and that we could record this data once a week on a class data sheet as well as a data sheet in their notebooks. There are several ways that this can be managed:

  • Students can look up the data on an individual basis and record it in their notebooks
  • One student can be designated to look up the data each week and he or she can record the information on the class data sheet
  • This can be assigned as a weekly homework task
  • One person from each table or science group can be designated to look up and record the data.

Each student is responsible for recording the sunrise and sunset data on his or her recording sheet and calculating the photoperiod. They will also graph the data that they have calculated.

The data also will be graphed on a large class graph posted near the data sheet. Students also graph the photoperiod lengths on graph paper. Here is another photoperiod class data graph.

As we look at the data together, I bring the students back to the initial question I ask about why would a scientist want to know how much sunlight there is in a day and why would calculating this be important? Several students respond with that scientists need to know when seasons are, they need to know when to plant things, they need to know when living things use the sun. 

I also explain to them that scientists collect data and graph it so that they can use these graphs to explain their findings. 

I tell them that they will be answering some questions about this investigation (in the Evaluate section of this lesson) and I tell them that what we have learned about photoperiods will connect to later units we will doing.


20 minutes

After the students have figured out the photoperiods and graphed their data for the last few months, I have them look at the patterns they observe in the graph we have created and from their data collection and graphs.  

After our designated data collection time period we look at the graphs and discuss any patterns we see. Are the photoperiods longer or shorter? Was Daylight Savings Time a factor in calculating photoperiods?

What could scientists conclude from these patterns of photoperiods? 

I have the students look back to the original question I asked at the beginning of this lesson: 

Why would scientists want to know about a photoperiod or how much sunlight there is in a day? Why would this be important? 

I tell the student to use what they learned about collecting photoperiod data and answer this question in their science notebooks. I use their responses as an evaluation of their learning at the end of this lesson.

Several students notice that the photoperiods were getting longer as the weeks went on. There were 2 weeks when the length of the day was shorter, but then it got longer again. Some mention how Daylight Savings Time showed a shift in the sunrise and sunset times. 

My students also write about the importance of studying photoperiods by scientists which includes that they need to know about planting and when the best time to plant is. They also need to know about animal migration and why some animals are nocturnal while others are diurnal.