24 Hours of Light | ChandraBlog (2024)

International Day of Light
May 16, 2018

Light is something we experience every day. For most people, "light" refers to what humans can detect with our eyes. It is illumination, what ignites our visual sense, the yin to the yang of dark. However, the type of light humans can detect with our eyes is just a small fraction that exists, and the true nature of light is much more expansive.

In many ways, light behaves like a wave and this is the key to understanding its amazing capabilities. How tightly packed — or far apart — the waves are dictates light's properties. For example, the longer the wave, the less energy the light typically carries, and vice versa. Each type of light has its own "super powers" both in their natural forms and in ways sculpted by science and technology.

Picture a piano keyboard. The popular definition of light would inhabit a few keys around middle C, while the rest of the piano represents the full breadth of light and its many forms. On one end of the piano of light, there are radio waves. As you move up through the octaves, there are other forms of light including microwaves, infrared, "visible" light, ultraviolet, X-rays, and gamma rays.

The presence of light in our lives, particularly in its invisible manifestations, is so commonplace that most of the time we do not even take notice. May 16, 2018 has been declared the International Day of Light by the United Nations, and it is an excellent opportunity to explore the many ways we use and need light — in all of its forms — throughout our daily lives.

Here we look at some examples of light in our lives throughout the course of one day.

12:00 am: On a clear, Moon-less night we can see thousands of stars away from the light pollution of urban areas.

1:00 am: The cosmos has much more than meets the unaided human eye, however. Most cosmic objects — including stars — emit light in many forms, spanning from radio waves to gamma rays.

2:00 am: As we are tucked warmly in our beds asleep, our bodies are radiating heat. This heat is invisible to us, but it is detectable as infrared light by specially-designed cameras.

3:00 am: As they prepare the early morning weather forecast, meteorologists consult satellite imagery that contains data in microwave light that can penetrate clouds and reveal precipitation.

4:00 am: Making their way back their roost, bats catch food by sending out radio waves (which are converted into sound waves) and using the echoes to "see" their prey.

5:00 am: Sunlight begins to peek through your window, signaling the start of a new day. Although it emits the yellow band of visible light most strongly, our Sun gives off light in many forms.