In this lesson, we’ll learn what the chromosphere is and some facts about it. We’ll cover the location in the sun’s atmosphere, the temperature and the composition of the layer; you’ll also learn what spicules protruding from this layer are.

What Is the Chromosphere?

The year is 3050; you’re an astronaut on a space exploration off to study the stars and look for life on other planets. As you zoom past the sun, solar winds made of charged atoms fly around your ship. You see solar flares – huge spikes of flames extending out from the surface of the sun, emitting dangerous amounts of radiation. Luckily, your ship shields you from the energy that would otherwise vaporize you in an instant.

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As you cruise past this site, you wonder what the sun is really made of. Where are those solar flares coming from? What causes the beautiful red glow? Today, we’re going to investigate one layer of the sun: the chromosphere.

The chromosphere is the second, gaseous, outer layer of the atmosphere of the sun. It stretches from about 250 miles from the sun’s surface to 1,300 miles upward, making the chromosphere 1,050 miles thick. To get an idea of the scale of this distance, picture driving from San Diego to Seattle up the California Coast. This drive is about 1,255 miles depending on your route, a little more than the thickness of the chromosphere.

Temperature of the Chromosphere?

Probably one of the hottest temperatures you’ve encountered on Earth comes from a campfire, which on average burns at about 2,012 degrees Fahrenheit. Although fire is one of the warmest parts of our daily life, the chromosphere’s temperature ranges between 6,700 and 14,000 degrees Fahrenheit. At this temperature, molecules absorb so much energy, that they transform from gas to plasma, a state where atoms pick up a charge, becoming ionized. This fourth state of matter contains the most energy and isn’t regularly found on Earth.

The inner layers of the sun increase in temperature as you move closer to the sun’s core. However, the atmosphere of the sun gets hotter as you move from the chromosphere of the sun to the outer layer of the atmosphere, the corona. The chromosphere is the coolest where it begins at 250 miles from the surface of the sun, and the hottest farthest away from the surface of the sun at the outer edge, 1,300 miles out. Scientists aren’t totally sure why this happens, but they think it has to do with the magnetic field of the sun. Magnetic fields and electrical fields, like those created from the ions in the plasma, can interact.

In the chromosphere, there are intense magnetic storms that can stir up the plasma, causing the temperature to rise as we move further away from the sun’s core. Imagine it like a chemical reaction, but for forces and energy. If you’ve ever mixed baking soda and vinegar, you know the two compounds react with each other, causing an explosion of bubbles. Imagine the magnetic fields are like the baking soda, and the electric energy in the plasma is like the vinegar. When you mix them together in the magnetic storms, they cause an explosion, seen as a rapid increase in temperature.

Composition

So, what is all this plasma made of anyway? It’s hard to imagine a substance on Earth that would survive temperatures of 14,000 degrees Fahrenheit. The outer layers of the sun, like the chromosphere, are made of mostly hydrogen, and some helium gas in the form of plasma. Although only visible during a solar eclipse, the chromosphere is red in color. In fact, the chromosphere was originally named as such due to the red color. Chromo means color, and sphere refers to it as a circular layer around the sun. The ionized hydrogen gas emits energy that can be seen as red visible light on Earth.

The other gas composing the chromosphere, helium, was first discovered on the sun. In 1868, the British astronomer J. Norman Lockyer, first proposed the existence of this new element. It wasn’t until 1895 that the element was isolated in a lab on Earth and Lockyer’s results were validated.

Spicules

Spicules are dense explosions of gases that are characteristic of the chromosphere. The spicules feed plasma into the corona, providing fuel for solar flares, the jets of flames we see jumping around the surface of the sun. Spicules travel quite fast, starting from the lower chromosphere. Traveling at about 12 miles per second, they reach the corona within 10 to 15 minutes and then collapse. Scientists think spicules are caused by changes in the magnetic field in the photosphere.

The process starts with large sound waves emanating from the interior of the sun. The sound waves are pushed through the core to the photosphere through magnetic field channels. As the sound waves flow outward, they push the plasma out also, causing the jets of plasma shooting out of the chromosphere to form.

Think of it like squeezing toothpaste from a tube; the plastic container is like the magnetic field, providing a channel for the plasma. When you squeeze the toothpaste, it squirts out the other end. Picture the sound wave like your hand and the toothpaste like the plasma. When the sound wave pushes the plasma, it squirts out the magnetic field channel as a spicule.

Lesson Summary

The chromosphere is the second outer layer of the sun’s atmosphere, extending from 250 miles to 1,300 miles above the surface of the sun. Temperatures in the outer chromosphere can soar to 14,000 degrees F. The chromosphere is mainly made of hydrogen and helium plasma, which is ionized to produce red visible light, as seen during an eclipse.

Currents in the plasma caused by sound waves in the core produce spicules, large jets of gases that shoot into the corona but quickly collapse back into the chromosphere in about 10-15 minutes.