DFRobot Science Lab Season 2
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EP02: Why Does the Moon Shine at Night?
Introduction
Standards
NGSS
4-PS4-2 Build a physical model to explain that when the light reflected by an object enters our eyes, the object can be seen.
5-ESS1-2 Present data in charts to illustrate how the length and direction of shadow changes throughout the day, the alternation of day and night, and seasonal changes of stars.
Science - Grade 3-5
Overview
Introduce the light of reflection principle to students starting from the question “Why does the Moon shine at night?”, then lead them to observe the phenomenon of light reflection by experimenting to recognize the nature of light.
Materials
Play and Learn with Boson Science Design Kit: https://www.dfrobot.com/product-2176.html
Engage
We often see the moon shining in the dark sky. The moon itself does not produce any light of its own, but why does it seem bright at night? And if we observe it carefully enough, we can find that the moon is not uniformly bright and there are dark shades all over it. Why is that?
Take a guess!
Explore
After making suppositions about the unknown question, let’s test them by experimenting.
The first part of the experiment will mainly explore the question “why does the moon shine at night?”. Then we will move on to the second part to discuss “why the moon is not uniformly bright?”.
Part 1 Why does the moon shine at night?
Preparation
Use a flashlight (can emit light) to simulate the sun, take a white foam ball (cannot emit light) as the moon, and the BOSON light sensor as the human eyes to detect the intensity of light. Observe and think about why the moon shines at night in the experiment.
Step
1. Build an experimental circuit to detect the intensity of light using the light sensor.
2. After the circuit is built, put it in a big paperboard box (if you can complete it in a dark environment, then the box is not necessary), point the round detector of the light sensor at the inner side of the box, as shown below. It is suggested to fix the light sensor onto the box with adhesive tape to ensure the accuracy of the experimental results.
Carry out the three experiments below, and record the results in the form.
Activity Conclusion
Imagine, if we do this experiment in a very dark environment, then we can’t see anything before the flashlight is turned on.
When turning on the flashlight, the light emitted from the flashlight enters our eyes so we can see it. The foam ball does not produce light, but it reflects the light of the flashlight into our eyes so it can be seen by us too.
We can see objects that do not produce light because they can reflect light.
For instance, at night, we turn on the lamp for reading. The light from the lamp enters our eyes so we can see it. The book cannot shine, but the lamp’s light shines on the book and is reflected into our eyes by the book, as a result, the book can be seen by us.
Likewise, the moon itself does not emit light, but its surface reflects light from the sun, so we are able to see it.
Now, you must have known why the Moon shines at night!
Make a Conjecture
In the experiment above, the detected light data becomes larger gradually from the first to the third group.
When the flashlight is turned on, the paperboard box can be seen, indicating that the box can reflect light. After putting the white foam ball inside the box, the detected light value gets larger and the ball looks brighter than the box, from which we can infer that the white foam ball can reflect more lights than the paperboard box.
Do different objects has the same ability to reflect light? In the environment with a same light source, does the object with stronger reflection look brighter?
Then let’s go back to the previous question, why doesn’t the moon seem uniformly bright? Would it have something to do with the surface of the moon? Fill your supposition in the table below:
Part 2 Why doesn’t the moon seem uniformly bright?
We can suspect based on the analysis above that the light and dark patches on the moon are related to the different abilities of the moon’s surface to reflect light.
To test different objects’ ability to reflect light, we can use a mirror to carry out contrast experiments. The two sides of a mirror would be the experimental objects here since they are in the same size, which can avoid the effect of size difference on the light reflection. Complete the experiments below and record the result in the table.
Preparation
The circuit built in the previous experiment will be still used here. The two sides of a mirror will be the experimental objects.
Conclusion
The experiments show that the mirror front side performs a stronger ability to reflect light compared with its back side, which states that the light reflection ability of different objects appears to be distinct, and the metal-coated surface can reflect more lights than a plastic surface.
The moon is like a big stone that doesn't shine. The moon’s surface had what looked like valleys, plains and highlands much like the distinctly unheavenly surface of the Earth. Moreover, the material composition of these places is also various. The moon highlands are mainly composed of light-colored rocks, and have a strong ability to reflect sunlight. So, when the sun shines on the highlands, they seem brighter. While the valleys areas are often covered by black volcanic rocks that have a much weaker ability to reflect light. Then, of course, they look much dimmer by contrast.
So now you may understand why the moon is not uniformly bright!
Science Background
In our daily life, there are a lot of objects that can make light, and we call them light sources. On the contrary, the objects that cannot produce light themselves are non-light sources. Through the experiments, we learn that human beings can see objects that do not shine by the reflection of light. Now let’s get to know the light sources and non-light sources!
Light Source & Non-light Source
In physics, objects that can make light are called light sources, like the sun, fluorescent bulbs, burning candles, etc. The objects cannot emit light are non-light sources, such as table, chair, wall, paper, etc.
Reflection of Light
Reflection of light is the change in direction of a light ray at an interface between two different media so that the light returns into the medium from which it originated. It is because of the reflection of light that we can see objects that do not emit light.
Specular reflection and diffuse reflection
The reflection of light can be roughly categorized into two types: specular reflection and diffuse reflection.
Specular reflection is defined as light reflected from a smooth and shiny surface at a definite angle, for instance, when a light beam falls on a surface like glass, water or polished metal, it reflects at the same time as it hit the surface.
Diffuse reflection is the scattering of light that occurs when it reflects off rough surfaces such as clothes, rocks, etc. Unlike specular reflection, which is calculated based on the surface angle, diffuse reflection is calculated based on the structure of the surface itself. For instance, a rough surface will reflect light at many angles, depending on its bumps, divots, and grain. Even a very smooth surface, like a wall, produces a diffuse reflection at many angles, due to the molecular structure of the material. Diffuse reflection contributes mostly to identifying the object when compared to specular reflection.
Specular reflection and diffuse reflection often occur simultaneously. For example, sometimes, we may find the specular reflection on the blackboard since it comes with a very smooth surface, which makes it hard for us to see the contents on it clearly. But, the lights from the diffuse reflection of other objects like, ground and wall, can help us identify the words on the blackboard.
Think about it, when we look in the mirror, what kind of reflection happened? Can you find some specular and diffuse reflection phenomena in our daily life? What are the effects of specular reflection on our everyday life?
Conclusion
In this project, we mainly talk about the question “why does the moon shine at night?”, and get known to the reflection of light by experimenting, as well as have a rough understanding of the basics of specular reflection and diffuse reflection.
Then that’s all for this lesson. Put all BOSON modules and tools back to the original place.
Extend
1. The moon’s shape appears to be various at different times of a month, why does the moon change shape?
2. It seems that the moon always shows the same side to us, can we see other sides of the moon?
Appendix – Why the moon change shape?
In the universe, the sun is a star, the earth is a planet, and the moon is the permanent natural satellite of the earth. The moon rotates on its axis and revolves around the earth as the earth revolves around the sun. The moon’s period of rotation and revolution are identical. So, one side of the moon always faces the earth.
Although we can only see one side of the moon, the moon may have different "shapes" in a month. It could look like a full circle, a half circle, a crescent, or sometimes it is even invisible. Why is that？Let’s find out the answer through a simple experiment.
First, find a dark room (the darker, the better) to simulate the cosmic environment, prepare a table lamp to simulate the sun, think of our own head as the earth, and a white foam ball as the moon. Then the "Sun-Earth-Moon" models are corresponding to the "lamp-head-foam ball".
Step
1. Carefully piece the ball with the pencil, and hold it with your one hand.
2．Stand with the white ball at arm’s length in front of the sun(lamp), and keep turning to the left slightly to simulate that the moon(ball) rotates around the earth (your body).
3. The lamp is the model of the sun. Keep turning your body to the left while observing how the lighted portion of the ball looks at different positions.
* Video for reference:
Conclusion
We have known that the moon shines because its surface reflects light from the sun. In this experiment, as the moon orbits the Earth, we see the different parts of the lighted area. The revolution of the Moon around the Earth makes the Moon look as if it is changing shape in the sky. These are called phases of the Moon. Refer to the figure below to see if the results of your observation are consistent with the moon phase chart!
