Science Projects
1
2
3
4
5
473 reviews
Abstract
Have you ever looked up at the stars at night and wondered how fast they were moving or how far away they were? By studying how the brightness of a star changes with distance, you can answer those questions. In this astronomy science project, you'll create a model of starlight and use a sensor app with your smartphone to discover the key relationship between brightness and distance.
Summary
Areas of Science
Astronomy
Science With Your Smartphone
Difficulty
Time Required
Very Short (≤ 1 day)
Prerequisites
None
Material Availability
Readily available
Cost
Very Low (under $20)
Safety
No issues
Credits
Kristin Strong, Science Buddies
Sabine De Brabandere, PhD, Science Buddies
Objective
To determine how the light intensity of a point source of light, like a star, changes with distance from that source.
Introduction
Do you love looking at the stars? No, not the Hollywood kind—the ones in the sky! For thousands of years, people have looked up at these faithful pinpoints of light and wondered about those "diamonds in the sky." They have used stars as centerpieces for religions, fuel for legends and myths, tools for navigation, and as predictable calendars for planting crops. In 1584, though, Giordano Bruno suggested that the stars were objects, much like the Sun, just farther away. This idea upset a lot of people, and he was actually killed for this and for other beliefs. It would take more than 250 years for people to accept that Bruno was right and take their first distance measurement from Earth to a star.
Figure 1. A photo, taken by Science Buddies founder Kenneth Hess, of 100 billion stars in the Milky Way at the Golden State Star Party. (Kenneth L. Hess, 2009.)
To find out just how far away a star is, scientists first had to figure out how the light intensity of a point source of light, like a star, changes with distance. Light intensity is a measure of how much light falls on a certain area, like one square meter. Scientists experimented and predicted that the relationship between intensity and distance would follow an inverse-square law. This means that as the distance from a light source doubles, its light intensity decreases by a factor of four, (which is the square of the factor of change). This is illustrated in the Figure 2, where the red dot, the point source of light, has a light intensity we will name L0 for this example, at one unit (it could represent any unit) away from the light source; but as you double the distance to two units away, the intensity goes down by a factor of four. At three units away, the intensity goes down by a factor of nine, and so on.
A point of light spreads out in an increasing pattern of squares to represent the inverse-square law. As light travels a certain distance, the intensity of the light will decrease by a square of the distance. The smallest square is closest to the point of light and is the brightest. The second light square is twice as far from the light source as the first square, so the light intensity decreases by a factor of 4. The third square is 3 times the distance as the first so the light intensity decreases by a factor of 9. The fourth square is 4 times the distance as the first so light intensity decreases by a factor of 16. Finally the last square is the least bright as it is 5 times the distance from the first and the light intensity decreases by a factor of 25.
Figure 2. This drawing shows how light follows an inverse square law. Notice that as the distance increases from the light source (the red dot), the light must spread out over a larger surface area, and the light intensity at the surface decreases by the distance squared. (NASA, 2006.)
In this astronomy science project, you will set up an experiment to re-create what scientists discovered about the relationship between light and distance. When you are done, think about what you would need to know to calculate how far away a star is from Earth.
Terms and Concepts
- Intensity
- Point source
- Inverse-square law
- Square
- Factor
- Lux (lx)
- Linear
- Inverse
Questions
- Why do you think stars are approximated as point sources, even though they are much bigger than Earth?
- Based on your research, how is it possible to measure distance of stars from changes in the light intensity of a point source?
- Can you think of any other laws that follow an inverse-square relationship?
Bibliography
This source provides a history of stars:
- Cain, F. (2009, February 10). History of Stars. Retrieved March 17, 2010.
These sources explain the inverse-square law for light and how changes in brightness can be used to measure distance and velocity (speed and direction) of a star:
- Newman, P. (2006, January 30). More on Brightness as a Function of Distance. National Aeronautics and Space Administration,Goddard Space Flight Center. Retrieved March 17, 2017.
- Newman, P. (2006, January 30). Observing the Light Intensity of M31. National Aeronautics and Space Administration,Goddard Space Flight Center. Retrieved March 17, 2017.
Materials and Equipment
- Bulb socket with cord and lightbulb (any wattage) or lamp with removable shade with a lightbulb (any wattage), detailed specifications can be found in the Procedure.
- Measuring tape
- Room that can be darkened well and cleared of objects in a 6-foot by 6-foot area
- Material to align the phone with the light source. This could be a ball of clay, an easel, a camera stand, etc.
- Graph paper
- Optional: Material to cover shiny objects. This could be black posterboard, dark colored sheets, etc.
- Smartphone with a sensor app such as phyphox, available for free on Google Play for Android devices (version 4.0 or newer) or from the App Store for iOS devices (iOS 9.0 or newer).
Note: Phyphox does not support the light sensor on iOS devices. If you need the light sensor, you have to use Android devices for your experiment. Note that on some devices the light sensor is only updated when there is a coarse change of illuminance. This means that if the light intensity does not change or only changes slightly, the sensor appears to not record any data. The recording will continue once the light intensity changes again. If your experiments allows, it helps to wiggle the phone or the light source (e.g. flashlight) slightly to induce minimal reading fluctuations and keep the sensor active.
- Lab notebook
Experimental Procedure
For this science project, you will use the light sensor of your smartphone to measure light intensity levels. Specific sensor apps such as phyphox let you record data using sensors that are built into many smartphones, including a light sensor. The light sensor measures light intensity in units of lux (lx), which is a measure of how much light falls on a certain area.
Note: Phyphox does not support the light sensor on iOS devices. If you need the light sensor, you have to use Android devices for your experiment. Note that on some devices the light sensor is only updated when there is a coarse change of illuminance. This means that if the light intensity does not change or only changes slightly, the sensor appears to not record any data. The recording will continue once the light intensity changes again. If your experiments allows, it helps to wiggle the phone or the light source (e.g. flashlight) slightly to induce minimal reading fluctuations and keep the sensor active.
Setting Up Your Experiment
- Familiarize yourself with the sensor app and the light sensor.
- Choose a light source.
- Any type of light bulb where the light shines equally in all directions is fine as a light source. Note that if you choose a lamp, you might need to remove the lamp shade so that the bulb is exposed. Figure 3 shows some good choices of incandescent and fluorescent light bulbs. The bulbs in Figure 4 direct light forward. Those do not work effectively to model stars.
Figure 3. Examples of incandescent light bulbs (right) and a fluorescent light bulb (left) that are good choices to model a star.
Figure 4. Directional light bulbs are not good choices to model a star.
Technical note:
You may notice that different light bulbs with the same power rating (or watt value) can yield different lux measurements. This is because a lux measurement favors some wavelengths (colors) over others in order to mimic the human eye's perception of light, and different types of light bulbs emit different sets of wavelengths. This is not a problem for this project, as you will only use one type of bulb.
- Find a place to take measurements.
- Find an area that is approximately two by three meters in a room that can be darkened (like a room without windows or one where you can close the window blinds if there are windows). For brighter bulbs, you might need a larger space.
- Remove shiny items that can reflect light.
- Be as far as possible from walls that might reflect light.
- Cover the floor with dark poster board or a dark-colored sheet if the chosen area has shiny or light-colored floors.
- Set up the light source, measuring tape, and phone. Figure 5 shows an example of a setup.
Some things to keep in mind when you design your setup:
- The light sensor on the phone needs to be at the same height as the light source. In the setup shown in Figure 5, this is done by placing the bulb on a ball of clay.
- Find a way to glide the phone in a controlled way towards or away from the light source. In Figure 5, the phone is resting on the ground. Other solutions are resting the phone on an easel, a camera stand, etc.
- Place the measuring tape in a way that you can easily read the distance between the light source and the light sensor.
Figure 5. Experimental setup to measure light intensity versus distance of a light source. Note that in your setup, the floor covering should be dark to reduce the reflection of light on the floor. The green arrow shows how the light source and the light sensor line up. The blue arrow shows that the light source is located at the 0cm point of the measuring tape.
Measuring
- Create a table like Table 1 in your lab notebook.
| Light Intensity Measurements | ||||
|---|---|---|---|---|
| Distance from light source [cm.] | Trial 1 [lux] | Trial 2 [lux] | Trial 3 [lux] | Average of trials [lux] |
Table 1. Table to record measured light intensity for varying distances from the light source.
- Darken the room. Do your best to eliminate as many stray sources of light as possible. Then, turn on the light bulb. People with sensitive eyes might want to put on sunglasses. Note: Some light bulbs need a few minutes to reach their maximum brightness. Wait until the bulb's brightness is steady before you start your experiment.
- If you are using the phyphox app, open the light sensor and go to the 'Simple' tab. In this mode, the app will display the measured light intensity as a numeric value. Then, start by holding the sensor relatively close to the bulb. Remember the light sensor must always be level with the light source. Move the phone away from the light source and determine a distance where the measurement is very low and changes minimally with changing distance. This will be your starting distance.
- This step describes how to measure and record a single data point at each distance with the phyphox app in 'Simple' mode. Optionally, you can also record data continuously while moving the phone toward the light source in constant intervals, as described in the Recording Data While Moving the Phone section.
- Hold the phone at the starting distance.
- Write down the distance in your lab notebook, read the lux measurement from your phone and record the measurement value in your table.
- Move the phone 5cm closer to the light source and repeat step b. Continue this until the light sensor is very close to the light source. To record higher-resolution data, reduce the distance between consecutive measurements from 5 to 2.5cm.
- Note: If your values start flickering, or you get unexplained low values, this could be due to interference between the sampling frequency of the sensor (how many data points it records per second) and the flickering of the light source, which might be flickering faster than your eye can see. If this happens, try one more time. If the issue persists, switching to a different light source or a different phone usually solves the problem.
- This finishes one trial. Repeat step 4 two more times for a total of three trials.
Recording Data While Moving the Phone
Optional: As an alternative to writing down the lux values while you do the experiment, the phyphox app allows you to record how light intensity varies over time. If done as described below, you can read the measured lux values for different distances from such a graph.
- To create the graph, open the light sensor in the phyphox app and select the 'Graph' tab.
- Put your phone in place at the starting distance you determined in step 3 of section "Measuring." Write the starting distance down in your notebook.
- Press the play button in the phyphox app to start a recording.
- Move the phone 5cm towards the light source every 10 seconds (s). Note a time axis is displayed on the phone while you are recording in graph mode.
- Press the pause button to stop recording and save your data. Make sure to label it appropriately. Do not forget to write the starting distance and the distance over which you shifted the phone every 10s. in your notes.
- Use the graph to fill in your data table. Here are some hints:
- The first 10 seconds of your graph were taken at the starting distance from the source.
- Every 10 seconds, the phone was moved a fixed distance (e.g. 5 cm) closer to the source. Can you find a formula to find the distance to the source at any given time?
- With the 'pick data' tool in phyphox you can view the X value (elapsed time) and Y value (measured light intensity in lux) of specific data points on the graph.
- Figure 6 shows an example graph over a period of 60 seconds, where the phone was moved closer to the light source about every 10 seconds.
- To record higher resolution data, do another trial and move the phone in smaller steps (e.g. steps of 2.5cm instead of 5cm).
The sample graph shows light intensity being measured over time with a minimum lux value of 252 and a max lux value of 8125. The plotted points rise slowly from 0 to 560 lux in the first 30 seconds and then from 560 to 2389 lux between 30 and 50 seconds. At the 50 second mark the lux values jumps from 2389 to over 8000 where the graph ends.
Figure 6. Example data from the phyphox app while moving the phone closer to the light source about every 10 seconds. The x-axis of the graph shows time in seconds [s] and the y-axis is light intensity in lux.
Analyzing Your Data Table
- Calculate the average light intensity for each distance from the three trials and record your calculations in the last column of your data table.
- Make a line graph that plots the distance (in cm) on the x-axis and the average light intensity (in lux) on the y-axis.
- Looking at your graph, can you find a relationship between light intensity and distance to the light source?
- Does light intensity increase or decrease with distance?
- Is the relationship linear, meaning you can draw one straight line so all data points are close to this line? Or does it look like the data points follow a curve?
- If it looks like a curve, is the light intensity equal to a constant divided by the distance (indicating an inverse relationship), or, is the light intensity equal to a constant divided by the distance squared (indicating an inverse-square law)?
- What happens when you get very far away from the light source? Does the law you discovered in previous steps still hold? If your law does not hold there, why could this be? Could you change your setup so the law governs a wider range of distances?
Ask an Expert
Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.
Post a Question
Variations
- What happens with a light source that is not a point source, but is directed, like a flashlight? Redo the project using a flashlight or other directional light. Note: Do not use a laser for this project! There is a high risk of eye damage from looking into a laser.
- In this science project, you tested one light bulb. You can also verify if the relationship holds over several types or different powers of light bulbs.
Careers
If you like this project, you might enjoy exploring these related careers:
Physicist
Log in to add favorite More Menu
- Read More
Career Profile
Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to… Read more
Astronomer
Log in to add favorite More Menu
- Read More
Career Profile
Astronomers think big! They want to understand the entire universe—the nature of the Sun, Moon, planets, stars, galaxies, and everything in between. An astronomer's work can be pure science—gathering and analyzing data from instruments and creating theories about the nature of cosmic objects—or the work can be applied to practical problems in space flight and navigation, or satellite communications. Read more
Related Links
- Science Fair Project Guide
- Other Ideas Like This
- Astronomy Project Ideas
- Science With Your Smartphone Project Ideas
- My Favorites
News Feed on This Topic
, ,
Cite This Page
General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.
MLA Style
Science Buddies Staff. "Star light, Star bright: How Does Light Intensity Change with Distance?" Science Buddies, 3 Mar. 2022, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Astro_p034/astronomy/how-does-light-intensity-change-with-distance. Accessed 26 Feb. 2023.
APA Style
Science Buddies Staff. (2022, March 3). Star light, Star bright: How Does Light Intensity Change with Distance? Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Astro_p034/astronomy/how-does-light-intensity-change-with-distance
Last edit date: 2022-03-03
Explore Our Science Videos
Make a Straw Siphon
Make a Straw Siphon
DIY Mini Drone Part 2: Altitude Control Circuit
DIY Mini Drone Part 2: Altitude Control Circuit
Self-Driving Cars Science Project: Automatic Braking
Self-Driving Cars Science Project: Automatic Braking
FAQs
How does the distance affect the brightness of a star? ›
This relates the Apparent Brightness of a star (or other light source) to its Luminosity (Intrinsic Brightness) through the Inverse Square Law of Brightness: At a particular Luminosity, the more distant an object is, the fainter its apparent brightness becomes as the square of the distance.
How does distance affect the apparent brightness of an object? ›The smaller the distance between the observer and object, the greater the apparent brightness.
What is the relationship between distance and brightness? ›That's why this is called the inverse-square law; brightness is inversely proportional to the square of the distance.
What is the relationship between the distance and the brightness of your light bulb? ›Increasing the distance between a light source and an observer always decreases the perceived brightness of the source. A mathematical relationship exists which relates apparent brightness b, the brightness which is perceived by an observer, to distance d.
What affects a star's brightness? ›The apparent brightness of a star depends on both its luminosity and its distance from Earth. Thus, the determination of apparent brightness and measurement of the distance to a star provide enough information to calculate its luminosity.
Why is the apparent brightness not enough to determine the distance to a star? ›However, apparent brightness is not an intrinsic property of the star; it depends on your location. So, everyone will measure a different apparent brightness for the same star if they are all different distances away from that star. For an analogy with which you are familiar, consider again the headlights of a car.
Does apparent brightness depend on distance? ›Apparent brightness is the rate at which a star's radiated energy reaches an observer on Earth. Apparent brightness depends on both luminosity and distance.
How do the distance size and temperature of the stars affect their brightness? ›As the size of a star increases, luminosity increases. If you think about it, a larger star has more surface area. That increased surface area allows more light and energy to be given off. Temperature also affects a star's luminosity.
How do you measure the distance of a star with brightness? ›By comparing the intrinsic brightness to the star's apparent brightness, we can get a good measure of the star's distance by applying the 1/r^2 rule. The 1/r^2 rule states that the apparent brightness of a light source is proportional to the square of its distance.
Does surface brightness change with distance? ›The surface brightness is the flux per unit solid angle of the image. The surface brightness is independent of distance (to first order). This is because the flux coming from an object decreases as 1/d2 for an object is located at distance d, while the solid angle subtended by the object decreases also as 1/d2.
Does light decrease with distance? ›
Light Decreases with Distance. Light intensity decreases with distance from source to receiving surface (sink), and the rate of decrease is in proportion to the square of the distance between emitter and receiver. This is called the Inverse Square Law.
Are distance and brightness directly or inversely proportional Why? ›The intensity of the light to an observer from a source is inversely proportional to the square of the distance from the observer to the source. This shows that as the distance from a light source increases, the intensity of light is equal to a value multiplied by 1/d2. Thus closer a light source brighter it is.
What happens to the brightness of the bulb if the current decreases? ›Therefore, when we decrease the current through the electric bulb, the amount of heat energy and thus the light energy decreases. That means, the brightness decreases.
How does the brightness of the bulb change? ›The brightness of a lightbulb is given by its power. P = I2R, and so brightness depends on current and resistance. If the bulbs are identical, they have the same resistance. They may not, however, experience the same current.
What happens to the light intensity if you double the distance to the source? ›The light intensity at any one spot increases as the area gets smaller and decreases as it gets larger. This observation is an example of a pattern called the inverse square relation. In an inverse square relation, if you double the distance the light becomes or as bright.
What is the brightness of a star called? ›magnitude, in astronomy, measure of the brightness of a star or other celestial body. The brighter the object, the lower the number assigned as a magnitude. In ancient times, stars were ranked in six magnitude classes, the first magnitude class containing the brightest stars.
What makes a star look brighter? ›The closer a star is to us, the brighter it will appear. Also, stars come in a variety of sizes and brightnesses. Larger stars usually shine more brightly than smaller stars do. So, how bright a star appears in the night sky depends on its size and how far away from us it is.
What two factors affect a star's brightness quizlet? ›What two factors determine how bright a star appears to be in the sky? A star's distance and luminosity determines how bright it appears in the sky.
What is determined by the actual brightness of the star and its distance from Earth? ›Apparent magnitude (m) is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's light caused by interstellar dust along the line of sight to the observer.
Is the brightness of the star from a standard distance? ›However, the brightness of a star depends on its composition and how far it is from the planet. Astronomers define star brightness in terms of apparent magnitude — how bright the star appears from Earth — and absolute magnitude — how bright the star appears at a standard distance of 32.6 light-years, or 10 parsecs.
How does distance affect the luminosity or brightness? ›
Notice that as the distance increases, the light must spread out over a larger surface and the surface brightness decreases in accordance with a "one over r squared" relationship. The decrease goes as r squared because the area over which the light is spread is proportional to the distance squared.
How does greater distance affect the appearance of an object's size and brightness? ›It's important to understand that a very bright object at a great distance can appear very dim because of its distance, whereas a dim object that is much closer can "look" brighter. Apparent magnitude is the brightness of an object as it appears in the sky as we observe it, regardless of how far away it is.
How would you relate the apparent brightness of light with the distance from the sources? ›The brightness or luminosity of a light source diminishes with the square of the distance according to the inverse square law.
How do we determine the distance of a star? ›By carefully measuring the angle through which the stars appear to move over the course of the year, and knowing how far Earth has moved, astronomers are able to use basic high-school geometry to calculate the star's distance.
What property of a star do we determine by first measuring its distance and brightness? ›Absolute Brightness / Luminosity
12.2) show that the apparent brightness of a star depends on both its absolute brightness (luminosity) and its distance to us. This makes sense: How bright a candle, car headlight, street light, etc. appear to us, depends on their true brightness and how far they are away.
In other words, the higher the throw distance, the less bright the image will be. If the throw distance is considerable, make sure you have enough output (lumens) on your projector to do so. Below are the 3 basic variables most affected by throw distance: Lumens – The brightness of the projector.
What is surface brightness in astronomy? ›In astronomy, surface brightness (SB) quantifies the apparent brightness or flux density per unit angular area of a spatially extended object such as a galaxy or nebula, or of the night sky background.
Why does light spread out over distance? ›Diffraction means that all waves – including sound, water, radio, and light – bend around corners. And it's not just the edge of the wave that bends around the corner. It is the entire wave. This means that a beam of light that is shone through a hole spreads out as it travels.
Does the brightness of light decreases when it goes nearer from its source? ›As light travels a certain distance, the intensity of the light will decrease by a square of the distance. The smallest square is closest to the point of light and is the brightest.
Will the brightness of the bulb increase/decrease or remain the same? ›Does the brightness of bulb A increase, decrease, or remain the same? Ans. Bulb A will become brighter.
When current increases what happens to brightness? ›
The brightness of the bulb depends on the amount of current flowing through it. When the current is increased, the brightness would also increase.
Does the brightness of a bulb depend on the direction of current? ›(c) No, the brightness of the bulb never depends upon the direction of current passing through it.
What determines brightness of light? ›Lumens measure how much light you are getting from a bulb. More lumens means it's a brighter light; fewer lumens means it's a dimmer light. Lumens let you buy the amount of light you want. So when buying light bulbs, think lumens, not watts.
Does higher current mean brighter light? ›For a classical (incandescent) light bulb, the more current that flows through the filament, the brighter it glows. You can make more current flow through the filament by raising the voltage.
Why does the brightness of a bulb decrease? ›When resistance is connected in series, brightness of bulb decreases because voltage across the bulb decreases.
What is the relationship between light intensity and distance? ›There is an inverse relationship between distance and light intensity – as the distance increases, light intensity decreases. This is because as the distance away from a light source increases, photons of light become spread over a wider area.
What is the relationship between intensity and distance? ›This principle is known as the inverse square law: intensity is inversely proportional to the square of the distance from the source (I ∝ 1/d2).
How does distance affect the appearance of stars? ›All the stars we see in the night sky are at vast distances from us but some are much closer relatively than others. For two stars of identical size and temperature, the closer one to us will appear brighter. An analogy is a row of street lights, the closer ones appear much brighter than those in the distance.
Are farther away stars brighter? ›A star's brightness also depends on its proximity to us. The more distant an object is, the dimmer it appears. Therefore, if two stars have the same level of brightness, but one is farther away, the closer star will appear brighter than the more distant star - even though they are equally bright!
Does the brightness of a star tell you how far away a star is? ›There is a direct relationship between the length of a Cepheid's pulsation and its true brightness. Measuring a Cepheid's apparent brightness -- how bright it looks from Earth -- allows astronomers to calculate its true brightness, which in turn reveals its distance.
Does the distance between the stars increase? ›
The stars in our Milky Way galaxy and in nearby galaxies are not increasing in their distance from the earth, despite the expansion of the universe.
Why are farther stars brighter? ›A star that outputs more light will be able to have its light reach further out into the distance of space than one that outputs less light. Distance is also a key factor, since it means that the light will disperse more or less depending on how far away the star is.
What can I calculate if I know the brightness of a star and the distance it is from Earth? ›Knowing the distance and apparent brightness of a star, we can determine its intrinsic luminosity using the equation f=L/4`pi'd2.
Are most of the brightest stars close or far away? ›The closer a star is to us, the brighter it will appear. Also, stars come in a variety of sizes and brightnesses.
Does star apparent brightness depend on just its distance from Earth? ›Apparent brightness is the rate at which a star's radiated energy reaches an observer on Earth. Apparent brightness depends on both luminosity and distance.