Wednesday, April 3, 2024

SearchResearch Challenge (4/3/24): Solar eclipses and shadows?

 I'm sure you've noticed... 

... that when you're walking through a group of trees, they cast shadows on the ground, dappling the surface with a lovely pattern of light and shadow.  

When I look up into the trees, I can see where the sunlight is coming from, and I'm struck by something: Why are some of the spots of light round when what I see in the trees is not round?  

Here's another view of light through trees: 

See those gaps?  The patches of light projected onto the forest floor are shaped like the openings in the tree canopy... mostly.  

But when the holes are small, the projected light is always circular.  In the image above, you can see that the large patches of light are soft rectangles, irregular blobs, and triangles with fuzzy edges.  When I look up into the tree, I see those rectangles, triangles, and irregular gaps in the tree cover.  

But when the hole is small, it always creates a small circular pool of light.  


That's our Challenge for this week.  Since there's a solar eclipse that's passing over the center of North America on Monday, April 8, I thought I should understand why the shadows are like that. 

Path of eclipse on April 8, 2024. P/C NASA.
I will be standing at the tip of the red arrow on April 8. 
Hope there are clear skies!

To prepare for the eclipse and the avalanche of shadows, I have a couple of Challenges: 

1. Why ARE the dapples of sunlight round in shape?  Why isn't the shape of the sunlight exactly like the shape of the hole in the tree canopy?  Related: Why are only the small patches of light round while the bigger ones are other shapes?  Super related: Will the round sun patches change shape during the eclipse? 

2. What other solar light phenomena should I be looking for?  Are there any other extraordinary shadow and light things I should be looking for?  

Of course, all this will happen next Monday--so I hope you post your answers to the blog before then so I'll know what to look for!  Tell us how you found your answers.  

Keep searching!  

(And wear eye protection if you're going to watch the eclipse.)  


  1. There are optical phenomena such as Bailey's Beads, the Diamond Ring and shadow bands, which are described here:

  2. And if it's cloudy, as is predicted for the San Antonio area where I'll be watching, Joe Rao writes in this article that the progression of the moon's shadow may be dramatically more visible than in clear skies, possibly even with some color changes:

  3. A map to know how the eclipse will look in your place

    Started with [tree canopy eclipse light shape]

    Unveiling the mystery of crescent-shaped projections during 'Ring of Fire' solar eclipse.

    The pinhole projection...You can also use a colander or other object with small holes to create your own pinhole camera.

    Google suggested:

    What is the pinhole effect on trees?

    Quora question: Why does light in the shadows of trees look circular?

    The circular spots of light shining on the ground vary in size depending on how high the canopy is above the ground;


    What If You Don't Have a Safe Solar Filter/Viewer?

    Other suggestions and how to do them:

    [solar light phenomena during eclipse]

    10 phenomena to see and photograph during April's total solar eclipse

    One of the mentioned in the article that is totally new for me: "...This phenomenon is known as the 'Purkinje effect' and occurs approximately four minutes before second contact and totality..."

    Beyond totality: Rare phenomena to watch out for during the solar eclipse

    1. In 1991 we were lucky to live total solar eclipse

    2. Eclipse was a great experience. Not as dark as the one in 1991 but very interesting and beautiful.

      I tried the trees and other and couldn't make it work. However, miraculously, my mobile captured it by luck. I still don't know how or why because Sun looks yellow but in the small circle the eclipse looks perfect

    3. The explanation of my happy accident. Lens flare. Thanks Dr. Russell :)

      Photos of eclipse by "luck and accident"

  4. The 'shadow bands' are kind of a cherry on the top of the whole eclipse dessert experience.

    Seems like they aren't explained very often (ever?) in the literature. But it was clear to our own family's physics major, what was happening at the end of the last eclipse, when we looked at the ground.

    When the first tiny bit of sunlight appears at the end of the eclipse, all the photons from the sun are aligned. This provides something of a free 'Schlieren Optics' setup, that makes the pressure of the wind visible. So the bands are letting you see the 'wavelength', of the speed of wind in the air. Very cool to see the invisible, made visible.

  5. there is much doubt in the shadow, not beyond,6&q=shadows+eclipse

  6. crescents - Yusuf -
    pinhole camera effect--
    optical shadows:
    "Patients most commonly notice a dark crescent temporally after surgery, relatively independent of the ambient lighting. "

  7. just landed in Portland, OR - very excited to see the eclip… wait, wha?? Portland, ME!?‽ ‽ - WDYM? NoNoTotality except in the Inane range? Portland,OR: 22.25%
    maybe Portugal 2026??
    "The total solar eclipse visits Maine on April 8, 2024 beginning at 3:28 pm EDT with the final exit of the Moon's shadow from the state at 3:35 pm EDT. Through Maine, the speed of the Moon's shadow will accelerate from about 2690 miles per hour to about 3175 miles per hour."
    should have gone to Houlton…
    "Some communities are in its path of totality and include most of Aroostook County. Houlton is the last town in the continental U.S. to see the event and one of the places to experience the longest period of total darkness in Maine. Other area towns along the path include Island Falls and Presque Isle."