オーロラの色が緑や赤になる理由は？光る高さと、ぶつかる空気で決まります

Why Is the Aurora Green and Red?

Have you ever seen the northern lights?

They are glowing lights that move across the night sky.

Most of them look greenish-yellow.

But what makes this light?

The story begins with the Sun.

The Sun sends out tiny charged particles called the solar wind.

Earth has a magnetic field, and it guides the particles toward the polar regions.

There, the particles hit gases high above the ground.

The gases are mostly nitrogen and oxygen.

Each hit gives a gas atom extra energy.

Then the atom gives the energy back as light.

This light is the aurora.

The color depends on the gas and the height.

Oxygen makes the two main colors, green and red.

Green light comes from about 120 to 180 kilometers up.

Red light usually comes from even higher up.

Nitrogen makes blue and violet light, mostly below 120 kilometers.

So an aurora does not happen near the ground.

It happens at least 80 kilometers above the Earth.

The strongest ones are as bright as moonlight.

Long ago, people sometimes thought a red aurora was a fire on the horizon.

Now you know the real reason.

Each color gives a clue about the gas and the height.

Next time you see a photo of the northern lights, look closely at the colors.