Things You Thought You Knew – Is Everything Light?

May 12, 2026

AI Summary

5 min read

In a 16th-century notebook, Leonardo da Vinci drew a ray of sunlight bouncing from the Earth to the moon and back again, solving a puzzle that had persisted since Genesis: why the darkened portion of a crescent moon is still faintly visible. The answer was Earthshine—sunlight reflected off our planet, then off the moon, then back to our eyes. And the property that makes this possible, the measure of how much light a surface bounces back, is called albedo.

Albedo: The Physics of Reflectivity

Albedo is a precise measurement ranging from zero to one—or zero to 100 percent. An albedo of 1.0 means a perfect mirror: all incoming light is reflected, nothing is absorbed. An albedo of zero means total absorption: no light bounces back. (Stars, for instance, have an albedo near zero because they generate their own light, but they absorb all external radiation that hits them.) The moon's albedo is about 0.1—roughly as dark as a car tire. It looks bright to us only because the sun is so overwhelmingly luminous. The Earth's average albedo is about 0.3, meaning 70 percent of the sunlight that strikes our planet gets absorbed, mostly by dark oceans and land. That absorbed energy stays here unless it can re-radiate back into space—which is where greenhouse gases enter the picture.

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What you'll learn

1 (03:21) **Albedo Defined** - Neil introduces the concept of albedo as a measure of reflectivity, ranging from zero to one (0% to 100% reflection).
2 (05:27) **Albedo Applied to Human Skin** - The conversation shifts to using albedo as a more scientific way to describe human skin color variation.
3 (07:10) **The Moon's Surprising Albedo** - Neil reveals the moon's albedo is surprisingly low, comparable to a car tire.
4 (08:39) **Albedo in Fashion and Climate** - Neil explains how albedo influences practical choices like clothing color and global temperature.
5 (10:15) **Earth's Albedo and Climate Implications** - The discussion turns to Earth's average albedo and its profound implications for global warming.
6 (12:07) **Earthshine: A Double Reflection** - Neil explains the phenomenon of Earthshine, where Earth's reflected light illuminates the dark portion of the moon.
7 (15:37) **Leonardo da Vinci's Discovery** - Neil credits Leonardo da Vinci as the first person to correctly explain Earthshine in the 15th century.

+ Full timestamped outline available in the app

Show Notes

How bright is the Earth from the moon? Neil deGrasse Tyson and Chuck Nice have fun with the sun’s reflectivity, discuss light pollution, and explore the electromagnetic light spectrum: how does sunscreen work?

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