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The STEM Zone - Build your own eclipse viewer

by Dr. Daniel Barth

It is NEVER safe to view any portion of the Sun with your naked eye — even during all phases of a solar eclipse except for the few moments of totality! To observe the eclipse safely you either need a pair of safe viewing glasses with solar filters (for one option, click here), or you need to construct a viewer that will let you see the eclipse safely without looking directly at the Sun. One way to be properly prepared is to build an eclipse viewer from a plastic drinking cup and a piece of graph paper. Technically, we will be making a pinhole camera and projecting the image of the Sun through it onto a piece of paper. When the Sun shines through a small round hole, it casts a round spot of light. Many people incorrectly assume that the spot of light is round because the hole is round – this is incorrect! The spot of light is round because the Sun itself is round! You can prove this to yourself by observing anywhere a tree casts its shadow on flat pavement or the side of a building. All the spots of light are round – because the Sun is round! (The gaps in the leaves are irregular in shape and change as the leaves move in the breeze.) Take a look at the photo to the right, which was taken during a partial eclipse in California. Each spot of light shining through the leaves shows up as a crescent – an image of the partially eclipsed Sun! Let’s build our own eclipse viewer!

COURTESY OF Daniel Barth

What you need:

  • Sturdy plastic drinking cup
  • Push pin or a brad nail
  • Several sheets of copy paper and a notebook or clipboard
  • Pencils, markers, etc.


  1. All that is needed is to push your pin or brad through the center of the cup’s bottom. A single, small hole is preferred.

  2. Hold the cup so that its bottom points directly at the Sun and hold your copy paper so that the projected image of the Sun falls on it. Keep the cup at a consistent distance from the paper.

  3. Hold the cup so that its bottom points directly at the Sun and hold your copy paper so that the projected image of the Sun falls on it. Keep the cup at a consistent distance from the paper.

  4. As soon as you see the Moon ‘take a bite’ out of the Sun’s image - trace the image you see as carefully as you can. Note the exact time on your paper.

  5. Make a new image every 10-15 minutes. You will see the ‘bite’ get larger as the Moon moves to block more of the Sun from view. Continue this through the entire eclipse event if you can.

Things to do with your solar eclipse data

Activity No. 1
Find the time of first contact (when the Moon first begins to cover the Sun) and last contact (when the eclipse ends). Compare these times with official data for your area. How accurate were you?

Activity No. 2
Find the time of maximum eclipse for your area – this will be the sketch that shows the largest area of the Sun covered by the Moon. You can project your image on fine graph paper (1-2 mm squares) to estimate the percentage of the Sun’s face that is covered by the Moon. How does this compare to the official estimates for your area?

Activity No. 3
Use sticky notes or note cards to make smaller copies of each sketch that you made. Bind them together into a flip-book that shows the progress of the eclipse!

What do we learn?

  • Although the total eclipse of the Sun is very brief, the entire solar eclipse event takes quite a long time – sometimes several hours.

  • The appearance of the Sun changes as more of it is covered – but we do not see a change in the light around us until most of the Sun is covered. This has to do with the way our eyes and brain process light.

  • When we compare data with students from across our area, we will find that the farther someone is from the path of totality, the smaller a portion of the Sun’s face will be covered by the Moon.


Dr. Daniel Barth left a career as a research scientist to teach. He has spent more than 30 years teaching astronomy, physics and chemistry at the high school and college level. A successful science fiction writer, Barth is the author of Maurice on the Moon, Doomed Colony of Mars and other works. He is currently assistant professor of STEM Education at the University of Arkansas in Fayetteville, and author of the Astronomy for Educators program.

Images are courtesy of Daniel Barth

Article from Sky's Up Magazine | July-September 2017