Why do shadows change during a solar eclipse?

Objects such as trees act as ‘pinhole’ projectors, producing nearly perfect images of the eclipsed Sun all around us

Images of the sun become more focused and change shape during a solar eclipse (Copyright KSAT 2023 - All rights reserved)

It’s one of the most fascinating things about a solar eclipse: dazzling crescents of light appear under trees. But why does this happen and what’s the science behind it?

KEY POINTS:

  • During a solar eclipse, the light from the Sun becomes more focused, creating clearer images of the Sun around us and...
  • As the Moon passes in front of the Sun, the apparent shape of the Sun is changed to a crescent, or -- in the case of an annular eclipse -- a donut!
  • This produces numerous images of the solar eclipse in the shadows all around us.

The everyday, made extraordinary

You may not realize this, but there are nearly perfect projections of the Sun every day all around us. Need proof? Step outside on a sunny day and look under a tree. You’ll notice fuzzy circles of light --that’s a projection of the circular image of the Sun! Here’s a picture of a driveway on Sunday, a regular sunny day without a solar eclipse:

Fuzzy circles of light, projections of the sun through the gaps in leaves of a tree on Sarah's driveway (Copyright KSAT 2023 - All rights reserved)

Notice the fuzzy circles of light? Those are projections of the circular Sun onto my driveway through the gaps in the leaves of a tree! The gaps in the leaves of the tree act as pinhole projectors -- just like the ones people make to view solar eclipses.

But how, during a solar eclipse, do these images change?

Less sunlight, clearer projection

On a regular sunny day, our star produces so much light it bounces and refracts off of many sources. This means that there are multiple points of light all around us other than the Sun. This is called ambient light. Ambient light causes shadows to become fuzzy.

During the partial phases of a solar eclipse, the amount of sunlight is reduced slightly, but the amount of ambient light is reduced greatly. So, projected images of the eclipsed Sun and shadows become sharper and clearer. Notice the shadows in the picture below, during an eclipse. Not only are the projections of the Sun sharper, but the shadow of the tree trunk is clearer, too!

Clear, sharp images of the solar eclipse and the trunk of the tree. Focused images because of the lack of ambient light. Image submitted by KSAT Connect user Liz Cheslock (Copyright KSAT 2023 - All rights reserved)

Shape-shifting Sun

Finally, we see crescent-shaped projections of the Sun because the apparent shape of our light source changes as the Moon moves in front of the Sun. In the case of the Oct. 14 annular eclipse, these projections were donut-shaped during the “ring of fire” peak of the eclipse!

Check out some of the pictures sent in to us on KSAT Connect:

Lillian

This was on our sidewalk during the eclipse Looks amazing

San Antonio
Marcia Caston

Eclipse on my shirt!

Bulverde
Mario Timberwood

Shadow of oak trees during the Eclipse

San Antonio
ConradGonzales

We took a picture of my wife’s car as the eclipse reflected through the tree! Conrad and Alma Gonzales

San Antonio
MayRay

Phenomenal eclipse shadows!

San Antonio

KSAT is Your Eclipse Authority station! We’re already getting prepared for the April 8, 2024 total solar eclipse. Stay tuned!!

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About the Author:

Sarah Spivey is a San Antonio native who grew up watching KSAT. She has been a proud member of the KSAT Weather Authority Team since 2017. Sarah is a Clark High School and Texas A&M University graduate. She previously worked at KTEN News. When Sarah is not busy forecasting, she enjoys hanging out with her husband and cat, and playing music.