light

We see light every day—whether from light bulbs, flames, flashlights, or the Sun (our most important source of light). We see objects because they reflect, or bounce, light into our eyes. Light is a form of energy called electromagnetic radiation. It's made of tiny particles called photons that travel in straight lines. In a vacuum, nothing can travel faster.

What it is: a form of energy
What it's made of: particles called "photons"
Speed: 186,000 miles per second in a vacuum
Mass: 0
Types of light: gamma rays, X-rays, ultraviolet light, visible light, infrared rays, microwaves, and radio waves
Characteristics: it can be absorbed, reflected, refracted, or passed through an object

Image credits: main image: Eric Hamilton.