Crisp Shadow At Home Demo
The next solar eclipse which will be visible in the United States will occur on April 8, 2024.
Here is an in home experiment you can do to understand why shadows get weird with an eclipse. Inspired by this video by SmarterEveryDay:
• EXTENDED CUT: 2024 Solar Eclipse Preparati...
If anyone wants to demo this at home:
1. Get the light you have with the largest size and cover up everything but a slit [or use a long inconsistent bulb light].
2. Shine it onto a wall in a dark room.
3. Hold something between the light and wall casting a shadow perpendicular to the strip of light you masked off.
4. Rotate the shadow caster 90 degrees to be parallel to the strip of light you masked off.
5. Your shadows will crisp up! Repeat as amusion and interest dictates.
The fundamental reason shadows shadows are fuzzy evaded me for a while. Thinking it might come from how round or opaque the edge of the shadow caster is, light diffusion, Fresnel, atmospheric scattering, or something else.
But the reason for fuzzy shadows is actually really simple. The sun itself has a size. Despite being very far away it is not a perfect point light. If it was a perfect point light all shadows would be perfectly crisp like in an old video game.
The distance ratio between a light source, shadow caster, and what the shadow is being cast onto does effect how fuzzy the shadow is; but only when the light itself has a size. If the light was a perfect point light this distance would not matter. With the expectation of uniquely reflective or refractive objects, all shadows would be perfectly crisp if the sun was a point light. That being said, perfect point lights do not exist outside of virtual rendering. So we can get to enjoy the fuzzy shadows.
If any of this is confusing do the demo! It really helped me understand the main reasons are fuzzy or crisp.