Letters on Sunspots

Published: February 23, 2026

Welcome to the new Sports and Science column, Letters on Sunspots. The title is inspired by Galileo Galilei’s book of the same name, in which he documents his observations of sunspots and argues that they were features on the sun’s surface, not separate celestial objects like Aristotle thought. Like this 17th-century gem, this column will explore the observations of the world around us. However, these concepts will be explained as simply as possible for readers who are new to science. 

Our first topic is: Why is the sky blue? This is one of the most common questions about our planet, yet very few people know the scientific explanation. A misconception is that big particles like dust and water are responsible for the sky’s blue color. Although dust, water, and pollution can make the sky hazier or give it a red hue, its common blue color is largely due to the tiny molecules that make up the air itself. These molecules, oxygen and nitrogen, are some of the most abundant gases in our atmosphere, and they play the leading role. 

The key to the color of the sky is the size of these molecules. In fact, they are much smaller than the wavelengths of visible light. The graph below depicts the spectrum of visible light, with the longest wavelengths appearing red, and the shortest appearing blue. Since the blue and violet rays are shorter, they are more likely to hit these minuscule oxygen and nitrogen particles in our atmosphere. When they do this, blue light gets reflected and scattered into all different directions, which is known as Rayleigh Scattering. 

Rayleigh Scattering was invented by British physicist John William Strutt (1842-1919). Strutt was the third Baron Rayleigh, a title in the peerage of the United Kingdom. In 1871, he published a mathematical proof that blue wavelengths in the atmosphere are scattered sixteen times more than the longer red wavelengths. 

Here’s where our topic gets a bit more confusing. As seen on the diagram, violet is the shortest wavelength. So why isn’t the sky violet? Ultimately, the human eye is significantly more sensitive to certain colors than it is to others, and blue is the color it can perceive best. Although violet light is what is being scattered around, we detect it as blue. 

Some animals, such as honey bees, hummingbirds, and mice, can see all the way to the ultraviolet range of the spectrum. Therefore, they likely perceive the sky closer to its true violet color. 

This column will also be accepting topic requests. If you have a scientific question you would like explained, you can email [email protected].