Unit 12: Safely Observing the Sun

Warning: NEVER look directly at the Sun! Not with sunglasses, not through a camera, definitely not with a telescope or a binocular, not even through a welder’s mask. NEVER LOOK AT THE SUN DIRECTLY!

These warnings sometimes make people (especially teachers!) shy away from solar observation activities – please don’t let this be you! Observing the Sun is fun and wondrous and can show students many interesting things, especially if you have the opportunity to observe a full or partial solar eclipse! Don’t let this terrific opportunity pass you by!

More than 40,000 students observed the Great American Eclipse in 2017 using the activities and curriculum from this book – and more importantly, everyone observed the Sun safely! You and your students can observe the Sun in perfect safety, too!

How can we observe the Sun safely? The trick is to project an image of the Sun onto paper, and look at that image instead of looking directly at the Sun itself. There are three easy ways to do this, we will look at the low-cost version first, then the high-tech version, then the no-cost version!

Activity 31. The Pinhole Camera

imagePinhole cameras have been known for centuries – actually long before the invention of photographic plates and film! The revelation that light shining through a tiny hole can create an image of what lies beyond is an exciting revelation that your children are sure to enjoy!

The pinhole camera used to be a more popular activity in the past when cameras were expensive and relatively rare. Miniaturized digital cameras are now on phones, and appear in the most unlikely places, taking away some of the awe and mystery of the camera. Even so, few people understand how a camera actually works, so making one of your own is a profound experience.

Academic Standards

Science and Engineering Practices

  • Developing and using models.
  • Planning and carrying out investigations.
  • Analyzing and interpreting data.
  • Argument from evidence.

Crosscutting Concepts

  • Systems and system models.
  • Structure and function.

Next Generation Science Standards

  • Space systems (K-5, 6-8, 9-12).
  • Engineering and design (K-5, 6-8, 9-12).
  • Waves and electromagnetic radiation (6-8, 9-12).
  • The Earth-Moon system (6-8, 9-12).

For the Educator

Facts you need to know

The Sun emits three basic kinds of light that reach the surface of the Earth: infrared light which we call heat, visible light, and ultraviolet light which is essential to our health in small doses but can damage skin and eyes if we are not careful. The trick when observing the Sun is to separate the visible light out from the rest! Fortunately, this is easier than it may seem.

Any time we shine sunlight through a small hole or a lens, we create a round image of the Sun. The bright circle of light isn’t round because the hole through which it shines is round, nor because the lens we use is round; the image is round because the Sun itself is round! This also means that during an eclipse, when the Sun’s image is not round, we should be able to observe this phenomena in action!

Teaching and Pedagogy

This lesson is as much about technology as it is about observations and data. One thing that you can focus on is what the pinhole camera is actually doing. In fact, there are several things going on at once! The aluminum foil is completely opaque – no sunlight passes through this thin layer of metal at all. By taking the light from the tiny hole and allowing it to expand into an image several inches across, you have eliminated almost all of the infrared and ultraviolet light and reduced the brightness of the visible light by several thousand times! This makes our image not only safe, but fun and easy to study and enjoy.

The image of the Sun also has much to tell us. If you can discern tiny dark dots on the solar image – sun spots! – then you will be very fortunate. These cool spots (really!) on the Sun’s surface are up to 1500 degrees colder than the surrounding areas. Cooler means that they shine more dimly, and thus appear dark to us. As it turns out, these sunspots are caused by magnetic storms on the surface of the Sun which allow extra energy to escape, cooling that region off substantially. The magnetic structure of the Sun is a bit beyond the scope of our STEM activities in this book, but it is fun to introduce children to these new ideas!

Student Outcomes

What will the student discover?

  1. The image of the Sun contains many exciting details that are normally hidden from us because we are blinded by the brightness of the solar disk. By cutting down on the amount of light, these details can be revealed with marvelous precision!
  2. Solar and lunar eclipses really do look very much the same. The bright object in the sky, whether the Sun or Moon, is gradually blotted out as a dark circle proceeds to cover it. This covering activity takes several hours, but with a solar eclipse, the time when the disk of the Sun is completely covered is very short indeed.

What will your students learn about science?

  1. Sometimes our scientific curiosity leads us into dangerous places or situations. Often times, the scientist’s answer to this is to create an instrument or mechanism that will allow us to observer and record what is happening in complete safety.
  2. Observing the Sun is our introduction to this important technique! Looking directly at the Sun is dangerous! Instead we will use instruments to filter out the light we want, and eliminate the more dangerous light we do not want so that we can observe safely!
  3. Safety First! This is the most important motto for the experimental scientist. Every responsible science teacher stresses – and teaches – safety as part of every lab activity. Every professional scientist thinks about safety as they plan and design experiments, no matter how big or how small.

Conducting the Activity

Materials

  1. A cardboard container. An oatmeal container works well.
  2. Scissors and hobby knife
  3. Lightproof tape (electrical tape or duct tape works well)
  4. White glue
  5. Aluminum foil
  6. Sewing pin

Building the Pinhole Camera Model

  1. Begin by cutting some holes in your cardboard box with scissors or a hobby knife. For the oatmeal box, cut a square opening about 5-inches on a side in the middle of the box; then cut a 1-inch square hole in the center of the box lid.
  2. If you are using a copy paper box, cut an 8-inch hole in the lid a bit closer to one end; next, cut a 2-inch square hole in the center of one end. Tape over any seams in the box with duct tapimagee to be sure they are light-proof. Cut a piece of white paper out that fits properly and glue it in the bottom of the oatmeal box. Once this is done, put the lid on and tape in in place with duct tape. If you are using the copy paper box, you can use a full sheet of paper and glue it in the end opposite the 2-inch hole. Once this is done put the lid on – the hole in the lid of the copy box should be closer to the end where you glued in the paper. Tape the lid in place securely with duct tape.
  3. Cut a square of aluminum foil large enough to completely cover the end of the oatmeal box and tape it over the end securely with duct tape, this will keep all stray light out of the box for you. Once this is done, puncture the foil carefully with a sewing pin. For the copy paper box, a 3-inch square of foil will be sufficient. Make as small a hole as you can! Smaller holes give dimmer, but sharper images. Larger holes make brighter, but somewhat fuzzier images. If the hole is too large, or if it gets damaged, you can always replace the foil easily. If the hole is too small (image is too dim to see), poke the needle into the hole again and enlarge it just a bit. Your pinhole camera is now ready to use!

Exploring the Pinhole Camera Model

  1. Hold the box over your head with the large opening in the side facing down, and the foil covered end facing the Sun. If you are doing this correctly, you should be able to look inside the box and see the white paper inside.
  2. Carefully adjust the direction you have the box pointed until you see a circle of light projected on the paper – this is the image of the Sun!
  3. Study the solar image carefully, you may see tiny black or grey dots on the solar surface – these are sunspots! With a separate piece of paper, try and map the sunspots you can see. Be aware that the Sun does not have sunspots every day! The solar activity cycle (more active means more sunspots) peaked in 2014 and has been declining. This cycle is 11 years long, and according to astronomers, we are in a period of weak solar activity anyway. Never the less, careful and patient observers will generally be rewarded with the sight of a few sunspots if they observe carefully once a week or so.
  4. If you have the opportunity to see a partial or complete solar eclipse, you are in for a treat! Your pinhole camera will show you the solar disk clearly, and when the eclipse begins, you will see a black “bite” being taken out of the Sun! As the eclipse progresses, the ‘bite’ will become larger; if you are lucky enough to see a total eclipse, the entire disk of the Sun will go dark!

Discussion Questions

  1. How does the pinhole camera make it safe to view the Sun?
    • Answer: The pinhole cuts out almost all the light.
    • Answer: We never look directly at the Sun – only at its image projected on paper.
  2. Why is the image of the Sun round in a pinhole camera?
    • Answer: Because the Sun itself is round!

Supplemental Materials

Going Deeper

You can find many interesting and fun to build designs for pinhole cameras on line, these are also called a Camera Obscura. Many of these designs show how to make a camera with a piece of translucent plastic for a screen.

You can actually project images of trees, landscapes, buildings, almost anything as long as it is well lighted.

Explore some camera obscura designs in your classroom and see what your class can discover about light and images.

Being an Astronomer

If you have the chance to observe an eclipse with a pinhole camera, try drawing a 0.5 cm grid on your projection screen with a fine, permanent marker. As you observe the progress of the eclipse, use the grid to estimate what percentage of the Sun or Moon is obscured by the eclipse.

One easy way to do this is to count the number of squares in the total image of the Sun or Moon (you only need to do this once), then count the number of squares that are darkened. The ratio between these two numbers will give you the percentage of the eclipse at that moment.

If you see a partial eclipse, try to estimate to greatest extent of the eclipse by percentage. Official values for eclipse percentage are often published for solar eclipses and are specific to your location. How close to you get to the official predictions?

Being a Scientist

Modern cameras use lenses to focus light. Find a simple magnifying lens and see if you can get it to project an image of a light bulb onto a piece of paper. How is this similar to your pinhole camera?

See if you can measure the distance between the lens and the focused image in millimeters – this is the focal length of the lens.

Measure the diameter of the lens in millimeters; this is also called the aperture. Now divide the focal length by the diameter of the lens, this is the focal ratio of the lens.

Following Up

Every modern camera and projector system uses lenses to focus and control light. How many examples of lenses in use can you find in your classroom? How about around your school?

Activity 32. The Binocular Projector

imageThis activity does the exact same thing as our pinhole camera – it allows us to examine the surface of the Sun safely by looking at a projected image. There are some important differences however! Unlike the pinhole camera, the binoculars do not dim the brightness of the solar image – instead they concentrate the light and brighten it substantially. The binocular projector is easier to use, there is no construction needed and it becomes very easy to draw or photograph the image which we have seen. The increased brightness makes it more difficult to make out subtle features like sunspots on the solar disk, the glare of the intense image tends to obscure them. For eclipse viewing however, this is an excellent method requiring almost no setup time.

Academic Standards

Science and Engineering Practices

  • Developing and using models.
  • Planning and carrying out investigations.
  • Analyzing and interpreting data.
  • Argument from evidence.

Crosscutting Concepts

  • Systems and system models.
  • Structure and function.

Next Generation Science Standards

  • Space systems (K-5, 6-8, 9-12).
  • Engineering and design (K-5, 6-8, 9-12).
  • Waves and electromagnetic radiation (6-8, 9-12).
  • The Earth-Moon system (6-8, 9-12).

For the Educator

Facts you need to know

  1. NEVER look at the Sun directly!
  2. Using only one pair of binoculars which remain in the teacher’s hands at all times, this activity is perfectly safe for all ages.
  3. We will use the binoculars to project an image of the Sun on paper.
  4. The projected solar image will be large enough and bright enough for an entire class to view it at once.

Teaching and Pedagogy

Once again, every science teacher teaches safety first! This activity makes safe observation virtually automatic. When you use the binoculars to project a solar image onto a piece of paper, students must stand with their backs to the Sun in order to view the projected image.

Using a pair of binoculars to project a solar image is simple in principle, but it requires practice to learn how to line up the binoculars, the Sun, and the paper. You will need to practice this activity several times before you do it in front of your students!

Take the binoculars and focus them for a distant object such as a tree or building at least 300 meters away. Remember to keep one side of the binocular covered, and start with the binoculars just a couple inches from the paper, then pull the binocular back until you get a large, sharp image of the Sun!

The Sun is different every day, sunspots and other features move slowly across the Sun. If you have a chance to try this activity during a lunar or solar eclipse, the effect is quite spectacular!

Student Outcomes

What will the student discover?

  1. A solar eclipse is a rare and wonderful event that is not to be missed. For many students, this will be a once-in-a-lifetime experience – do not allow them to miss it!
  2. The new Moon will at times be perfectly lined up to allow it to pass in front of the disk of the Sun, causing an eclipse.
  3. In order to see a total eclipse, you must be in exactly the right spot! The shadow of the Moon on the Earth’s surface is usually not more than 50 miles wide, and the shadow traces a path across the Earth called the path of totality. You must be inside this narrow path to see a total eclipse!
  4. Most people will not see a total eclipse, instead we get to see a partial eclipse because we are on one side or the other of the path of totality. This is still a wonderful event and worthy of our observation and study.

What will your students learn about science?

  1. People have been predicting solar eclipses for several thousand years. Scientists and mathematicians today predict these events with marvelous precision.
  2. Predictions are still just that – predictions made using a scientific model much as we have been doing throughout this book. Modern predictions of the timing and extent of a solar eclipse are not exact. This is a chance for students to see the precision – and the uncertainty – of modern science in one magnificent activity.

Conducting the Activity

Materials

  1. One pair of binoculars. Larger binocular work better for this, a pair of 7×50 binoculars work perfectly.
  2. A sheet of white paper on a notebook or clipboard.

Exploring the Binocular Projector

  1. imageCheck the binoculars on a tree or building to see that they are focused correctly.
  2. Put one of the lens caps on the binoculars so light only passes through one side. If lens caps are missing, use a piece of aluminum foil to tightly cap one side of the binoculars.
  3. Point the large end of the binoculars toward the Sun and hold the paper underneath the eyepiece. The paper may be anywhere from 1-4 inches away to give you the best image, this varies with styles and models of binoculars, so you will have to adjust this until you have the best view.
  4. You should now be able to observe the solar disk, sunspots, even an eclipse just as you can with the pinhole camera. The advantage of this method is that working with a partner, your students can easily draw directly on the paper they are observing and copy down what they see!

Discussion Questions

  1. How does the binocular projector make it safe to view the Sun?
    • Answer: We never look directly at the Sun – only at its image projected on paper.
  2. Why doesn’t the Sun look the same every time we look at it like the Moon does?
    • Answer: The Sun has no solid or permanent surface. The sunspots we sometimes see are magnetic storms on the solar surface, they appear and disappear as conditions change on the Sun’s surface, much as thunderstorms appear and disappear on Earth.

Supplemental Materials

Going Deeper

The binocular projector is also an excellent method to use when trying your hand at imaging the Moon. Take your binoculars out on a night when the Moon is at least half-full and try setting up to project the image on a piece of paper just as you did with the Sun. You will need a dark place to do this properly, yard lights and street lights will interfere with the image substantially. You will find that the projected image is substantially dimmer than the solar image, and this makes it much easier to pick up things such as dark maria and even some of the larger craters in addition to the shape of the lunar phase that night!

If you have a chance, try this activity with both a telescope and a binocular. You will find that the binocular projects an image just as you see it in the sky, while the telescope flips the image from side to side or even upside down! (This depends upon the type of telescope you use.) Optics are fun and mysterious – something your students will have the chance to explore further as they get older and enter higher grades in school!

Being an Astronomer

There are dedicated solar telescopes which allow you to look directly at the Sun and see many amazing features on the solar surface. Solar telescopes are specially built, single purpose machines, and quite expensive – even for telescopes!

Once again, it is time to contact your local astronomy club and ask for their help. Many clubs have a member with a special interest in the Sun who may own their very own solar telescope; some larger clubs purchase one of these specifically for the club to take out to schools and outreach events. If your local club has such an instrument, your students are in for a real treat!

Being a Scientist

If you are lucky enough to observe a solar eclipse through a binocular projector, you will find that the image is bright and well-focused enough to be easily photographed.

If you are able to take a photograph of the Sun every 5-10 minutes during an eclipse, the pictures can be combined into a GIF or time-lapse video to show how the Moon moves in front of the solar disk and put the Sun into eclipse!

Following Up

There have been many famous eclipse events in history and literature. Columbus’ eclipse during his exploration of the New World and Mark Twain’s A Connecticut Yankee in King Arthur’s Court both come to mind. How many others can you find?

Activity 33. The Tree Projector

Yet another method to project an image of the Sun safely during a solar eclipse. My students were able to observe and photograph the images of the Sun in eclipse using this method during the Great American Eclipse of 2017. Some were even able to use a kitchen colander to project multiple images of the Sun and photograph them!

Academic Standards

Science and Engineering Practices

  • Developing and using models.
  • Planning and carrying out investigations.
  • Analyzing and interpreting data.
  • Argument from evidence.

Crosscutting Concepts

  • Systems and system models.
  • Structure and function.

Next Generation Science Standards

  • Space systems (K-5, 6-8, 9-12).
  • Engineering and design (K-5, 6-8, 9-12).
  • Waves and electromagnetic radiation (6-8, 9-12).
  • The Earth-Moon system (6-8, 9-12).

For the Educator

Facts you need to know

  1. NEVER look at the Sun directly!
  2. Observing a projected image of the Sun on the sidewalk, this activity is perfectly safe for all ages.
  3. We will use the leaves in the trees – and the spaces between the leaves – to project an image of the Sun on paper.
  4. The projected solar image will be large enough and bright enough for an entire class to view it at once.

Teaching and Pedagogy

This one sounds a bit weird, but it really works! If you have a chance to see an eclipse, find a shady tree. Ideally, there should be some spots of sunlight shining through the tree onto the ground or a nearby wall. These spots of sunlight are actually projected images of the solar disk! As the eclipse progresses, you will notice that they are no longer “spots” of sunlight, instead they have become spots with a bite out of them! If the eclipse progresses far enough (more than 50%), you will see hundreds of bright crescents projected on the ground beneath the tree! This makes a beautiful and mysterious photograph if you can manage to capture it!

While in principle, this should also be possible with the Moon when it is lit more than half way, I have not been able to accomplish it. This could be an interesting challenge for your students to try!

Student Outcomes

What will the student discover?

  1. A solar eclipse is a rare and wonderful event that is not to be missed. For many students, this will be a once-in-a-lifetime experience – do not allow them to miss it!
  2. The new Moon will at times be perfectly lined up to allow it to pass in front of the disk of the Sun, causing an eclipse.
  3. In order to see a total eclipse, you must be in exactly the right spot! The shadow of the Moon on the Earth’s surface is usually not more than 50 miles wide, and the shadow traces a path across the Earth called the path of totality. You must be inside this narrow path to see a total eclipse!
  4. Most people will not see a total eclipse, instead we get to see a partial eclipse because we are on one side or the other of the path of totality. This is still a wonderful event and worthy of our observation and study.

What will your students learn about science?

  1. People have been predicting solar eclipses for several thousand years. Scientists and mathematicians today predict these events with marvelous precision.
  2. Predictions are still just that – predictions made using a scientific model much as we have been doing throughout this book. Modern predictions of the timing and extent of a solar eclipse are not exact. This is a chance for students to see the precision – and the uncertainty – of modern science in one magnificent activity.

Conducting the Activity

Materials

  1. You need an eclipse, and a leafy tree.
  2. A flat surface for the solar image to fall upon – a sidewalk works very well. If the Sun is low during the eclipse, you may find that the image will be nicely projected on the side of a building such as a house or garage.
  3. If you have no convenient flat surface around your tree, a flat piece of cardboard that has been painted white will do. A pizza box of something similar works very well.

Building the Tree Projector Model

  1. This model requires no preparation – you simply use the landscape to your advantage.

Exploring the Tree Projector Model

  1. I know of no other activity that inspires such wonder and amazement in children and adults alike. Watch and photograph the hundreds of solar images during the eclipse as they shimmer on the ground.
  2. As the eclipse progresses, the shape of the solar image on the ground will change. First you will see a small ‘bite’ out of the solar disk, then a large section will disappear, finally you will see only a thin crescent – hundreds of them – projected on the ground just before the Sun goes completely dark during totality!

Discussion Questions

  1. How does the tree create these images of the Sun?
    • Answer: The spaces between the leaves on the tree act just like the small hole in our pinhole camera.
  2. Why don’t we see solar images under the trees every day?
    • Answer: We do! The ‘dappled sunlight’ under a tree is hundreds of round images of the Sun. We take these round images for granted, not realizing what we see every day. Only during an eclipse, when the shape of the Sun changes dramatically do we see hundreds of crescent suns and stare in wonder!

Supplemental Materials

Following Up

Let all your parents know about your Tree Projector project. Encourage the parents from your class, and your students, to take as many photos of these delightful images as they can and post these photos in your class after the eclipse!

License

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Astronomy for Educators by Daniel E. Barth, PhD is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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