Investigating Star Brightness & Distance

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SWBAT explain how distance affects the appeared brightness of stars.

Big Idea

In this lesson, students explore the brightness of stars by examining a photo of the night sky. Then, students use flashlights to investigate how distance impacts star brightness.

Lesson Overview

Inquiry Based Instructional Model

To intertwine scientific knowledge and practices and to empower students to learn through exploration, it is essential for scientific inquiry to be embedded in science education. While there are many types of inquiry-based models, one model that I've grown to appreciate and use is called the FERA Learning Cycle, developed by the National Science Resources Center (NSRC):

1. Focus

2. Explore

3. Reflect

4. Apply

A framework for implementation can be found here

I absolutely love how the Center for Inquiry Science at the Institute for Systems Biology explains that this is "not a locked-step method" but "rather a cyclical process," meaning that some lessons may start off at the focus phase while others may begin at the explore phase. 

Finally, an amazing article found at, How Inquiry-Based Learning Works with STEM, very clearly outlines how inquiry based learning "paves the way for effective learning in science" and supports College and Career Readiness, particularly in the area of STEM career choices. 

Unit Explanation

In this unit, students begin by studying the location of the Earth in the Universe. Then, students learn about the brightness of stars through investigations and research. At the end of this unit, students explore the patterns on Earth, such as day/night and the length of shadows. 

Summary of Lesson

Today, I open the lesson by introducing key vocabulary words and coaching students as they come up with today's guiding question. Students then explore star brightness by analyzing a picture of the night sky. At the end of the lesson, students also explore how distance affects the apparent brightness of a star. Finally, students reflect and apply their new understanding of star brightness and distances by constructing a explanation. 

Next Generation Science Standards  

This lesson will support the following NGSS Standard(s):

5-ESS1-1. Support an argument that the apparent brightness of the sun and stars is due to their relative distances from Earth.  

Scientific & Engineering Practices

For this lesson, students are engaged in Science & Engineering Practice:

Science & Engineering Practice 2: Developing and Using Models

Students use a picture of the night sky and flashlights to analyze the brightness and distances of stars. 

Crosscutting Concepts

To relate ideas across disciplinary content, during this lesson I focus on the following Crosscutting Concept

Crosscutting Concept 2: Cause and Effect 

Students examine how closer stars can inaccurately appear to be brighter than stars that are located further away from the Earth. 

Disciplinary Core Ideas

In addition, this lesson also aligns with the following Disciplinary Core Ideas

ESS1.A:  The Universe and its Stars

The sun is a star that appears larger and brighter than other stars because it is closer. Stars range greatly in their distance from Earth. (5-ESS1-1)

ELA Integration

To add depth to student understanding, when I can, I'll often integrate ELA standards with science lessons. Today, students will work on meeting CCSS.ELA-LITERACY.W.5.2: Write informative/explanatory texts to examine a topic and convey ideas and information clearly. In this lesson, students will construct an explanation about star brightness and distance.

Choosing Science Teams

With science, it is often difficult to find a balance between providing students with as many hands-on experiences as possible, having plenty of science materials, and offering students a collaborative setting to solve problems. Any time groups have four or more students, the opportunities for individual students to speak and take part in the exploration process decreases. With groups of two, I often struggle to find enough science materials to go around. So this year, I chose to place students in teams of two or three! Picking science teams is always easy as I already have students placed in desk groups based upon behavior, abilities, and communication skills. Each desk group has about six kids, so I simply divide this larger group in half or thirds. 

Gathering Supplies & Assigning Roles

To encourage a smooth running classroom, I ask students to decide who is a 1, 2, or 3 in their groups of three students (without talking). In no time, each student has a number in the air. I'll then ask the "threes" to get certain supplies, "ones" to grab their computers, and "twos" to hand out papers (or whatever is needed for the lesson). This management strategy has proven to be effective when cleaning up and returning supplies as well!  


15 minutes

Partners & Computers

During today's lesson, students will be working in teams of two students (elbow partners). Each team of students will have one laptop computer to share. While we have enough computers for all students, I have found that partners are more successful collaborators when they are sharing one device. 

Envelope Book

For the Sun and Earth's Patterns Unit, students are creating an envelope book to help organize new information and to support an inquiry approach during the learning process. Prior to the unit, I used a plastic comb binding machine (pictured below) to create envelope books using 10 envelopes for each student's book: Envelope Books. During today's lesson, students will be working with the third envelope in their books. 

Vocabulary Cards

For each envelope, students are provided with up to 3 vocabulary cards: Vocabulary Cards (I copied these onto green card stock paper & cut each page into 10 cards): Vocabulary Cards. For easy distribution, I placed these cards into ziplock baggies so that each group of students could easily take cards out as needed: Vocabulary Cards in Bags. As an opening to the lesson, I write the following vocabulary words on the board: apparent magnitude and absolute magnitude.

Students work together with their partners to discover the meaning of each word, using their computers and/or dictionaries as resources. As students are ready, they share definitions out loud with the rest of the class. We discuss student findings and then I construct a student-friendly definition (using student input) for all students to record on their cards. This process is important for two reasons: (1) sometimes students record definitions that are difficult to understand due to complex language and (2) this also allows students to see how important it is to use multiple sources when conducting research. 

Here's an example of student vocabulary cards: Student Vocabulary Cards.

Developing a Guiding Question 

To support an inquiry-based learning model and Science & Engineering Practice 1 (Asking Questions and Defining Problems), I explain: Today, you will be learning about the brightness of stars. First, let's talk about the questions you have about star brightness. Think about the vocabulary words that we've discussed so far and think about what they have to do with stars and their brightness. What guiding question do you think we should research today? Student questions include:

  • When it says actual brightness, what does it mean by that... because is what we are seeing not its actual brightness? 
  • Can we measure the actual brightness of a star? 
  • How bright are most stars? 

As students share their thinking, I'm hoping that with some teacher guidance, students will reflect upon the vocabulary words and ask, "What effect does the distance form Earth have on the appeared brightness of stars?" Sure enough, after I give students a hint by mentioning the word, distance, one student asks, "Does it matter how far away a star is for how bright it is?" 

Here's a video of this question-development process in action: Students Developing a Guiding Question.

Lesson Introduction & Goal 

Now that students have helped develop a guiding question, I introduce today's learning goal: I can explain how distance affects the appeared brightness of stars. 

Envelope Cover 

I continue on by passing out an envelope picture to each student: Envelope 3 Pictures. Pictures add an element of excitement to learning and they provide support for students who learn best using visual aids. 

On the front cover of the third envelope in student envelope books, I model how to paste the picture and write the investigative question for today's lesson: What effect does the distance form Earth have on the appeared brightness of stars? (Student Example of Envelope).

As students are ready, we move on to exploring the brightness of stars and how distance affects the apparent brightness. 


30 minutes

For the exploration portion of this lesson, students will observe how the brightness of stars varies in the night sky by classifying stars and constructing a graph. 

Getting Ready

I want to provide students with the opportunity to study star brightness so I pass out a copy of page 37 of the following resource to each student: NASA: Sun as a Star Resource as well as a Star Brightness Tally Chart & Graph and a pink card (Pink Squares).

Before beginning, I ask students to turn and talk: What do you observe in this picture? Some students wonder if some of the bright objects are planets reflecting the sun's light. Others point out the different colors and sizes of the stars. Here, two students discuss why some stars are brighter than others: Students Making Observations.

Choosing a Sample

I ask: What would you say if I asked you to count and sort all of the stars in this picture? Students respond, "That would take forever!"

Sometimes, when an actual count will take too much time, scientists will look at a sample of all the stars. When choosing samples, scientists try to use a sample that represents the whole group of stars in the sky. Each of you have a pink square to help with selecting a sample. You'll select a sample of the stars in the picture by drawing an outline of the pink square (Teacher Model of Square). Will you want to choose a sample that includes all the brightest stars in the picture? Or a sample with only dim stars? Or will you want to find a spot on the paper that represents the night sky the best with some bright and some dim stars? This is important to go over as a sample should be representative of the population of stars as a whole. 

At this time, students outline their pink squares (Student Tracing Card) and start determining which stars are faint, medium, and bright.

Classifying Stars & Drawing Conclusions

As students are ready, they use the tally chart on the Star Brightness Tally Chart & Graph handout, to Classify the Stars within their sample (inside their outlined square) according to brightness. We discuss different methods of making sure the stars are counted accurately. Some students cross off the stars as they record their brightness. Others students divide their square into a 3 x 3 array so that the can analyze one portion of the sample at a time. 

When students finish classifying the stars in their sample, I ask partners to begin drawing conclusions based upon their findings.

Monitoring Student Understanding

During this time, I conference with as many students as possible. My goal is to support students by asking guiding questions (listed below). I also want to encourage students to engage in Science & Engineering Practice 7: Engaging in Argument from Evidence

  1. What patterns have you noticed? 
  2. Why do you suppose ____? 
  3. What have you found so far? 
  4. Has your thinking changed? 
  5. What evidence do you have? 
  6. How did you decide _____?
  7. What conclusion can you draw about ____?


Here, Students Draw Conclusions about Data, a student explains how there appears to be a lot more faint stars than bright stars. 

Graphing the Brightness of Stars

Next, students construct a graph using their recorded data. We begin by discussing how to choose an appropriate scale for the vertical axis by considering the highest data point. One student shares that her highest data point is 66 stars. I explain: The distance between one tick mark to the next is called the scale interval. What if the scale interval is two. Would we be able to fit our highest data point, such as 66 stars, on this graph? (No... we would only be able to graph data points at or below 14) How about if the scale interval is 5? (No... this would only take us up to 35) One student then offered, "I think we need to count by 10s!" We discuss how this scale interval allows us to graph any data with a value up to 70.

Students graph the number of faint, medium, and bright stars from their tally charts. This helps students visualize the brightness of stars in the sky. 

Reflect & Apply

30 minutes

At this point, many students believe that faint stars are smaller than bright stars. However, this isn't always the case! Before students reflect and apply on today's findings, I want students to also explore how distance can affect the brightness of stars! For this reason, I set up a quick demonstration for students to investigate how one flashlight can appear to be brighter than another, even though the two flashlights are of the same size and brightness. Today, students will complete Flashlight Investigation #1 and tomorrow, students will complete Flashlight Investigation #2. 

Flashlight Investigation Set Up

Prior to this lesson, I found Two Flashlights of the same size. I also made sure that each flashlight had new batteries as battery power can impact the brightness of flashlights and throw your entire demonstration off! 

I invite students to create the following t-chart on a lined sheet of paper: Flashlight Investigation T-Chart to encourage students to visualize the investigation using a diagram and to think about the investigation by drawing conclusions. Here's what the teacher model will look like when this investigation is complete: Flashlight Investigation #1 Teacher Model. As I model how to complete the t-chart throughout the investigative process, students also complete their own t-charts during this time: Example of Student Flashlight Investigation.

Flashlight Demonstration

For the First Part of the Investigation, two student volunteers hold the identical flashlights at an equal distance from the white board: Two Flashlights, Same Distances. I ask students to turn and talk: What do you notice? What conclusions can you draw about two stars that are the same brightness? After some time, we record a conclusion as a class (per student suggestions), "When two stars are the same size, they have the same absolute magnitude, or actual brightness." 

For the Second Part of the Investigation, two student volunteers hold the identical flashlights at two different distances: Two Flaslights, Different Distances. Students observe than the flashlight that is closer to the white board appears to be brighter that the flashlight that is further away from the whiteboard. Students agree to draw the following conclusion, "The closer the star is to Earth, the brighter it appears (apparent magnitude)." One student mentions, "That's why the sun seems bigger than other stars that are the same size or bigger... because it is closer to Earth!" 

This is pivotal moment in the unit as students are beginning to understand the Disciplinary Core Idea, 5-ESS1-1, The Universe and its Stars: The sun is a star that appears larger and brighter than other stars because it is closer. Stars range greatly in their distance from Earth. 

Sharing Findings

Now that students have built meaning and understanding by observing, questioning, and exploring, it is important to provide students with the opportunity to apply their findings. For this reason, I invite students to use their research to answer the guiding question, "What effect does the distance from the Earth have on the apparent magnitude (appeared brightness) of stars?" 

I pass out a copy of Flashlight Investigation Findings (cut into half sheets) to each student and I provide the following prompt to get students started: The farther away a star...

Teacher Note: By asking students to develop explanations based upon evidence and research findings, I am supporting Science & Engineering Practice 7: Engaging in Argument from Evidence.


As students finish, many students volunteer to read their explanations aloud. This allows others more time to complete their explanations. It also provides me with the opportunity to provide feedback and encourage precise language: Student Sharing Explanation.

Student Work

Here are a couple examples of student explanations. Most students grasped the concept that two stars can be the same brightness, but appear to be different brightnesses because of their distances from Earth. 



At the end of this lesson, students place the following items in today's envelope: