Chromosphere: Definition & Properties

Chromosphere: Definition & Properties
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  • 0:01 The Chromosphere
  • 0:41 What are Spicules?
  • 2:18 Why the Pinkish-Red Color?
  • 3:09 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will explore some of the interesting features of the second layer of the sun's atmosphere, the chromosphere, including spicules and its pinkish hue.

The Chromosphere

What's pinkish-red and invisible? It's a layer of the sun this lesson is going to cover in some detail. It's ordinarily invisible from Earth, unless you happen to see it during a total solar eclipse -- using some heavy-duty eye protection, of course.

That layer is called the chromosphere, a layer of gases directly above the photosphere, which in turn is the bright visible surface of the sun that gives us all that warm, pretty sunshine during the day. The chromosphere comes from the Greek 'chroma-,' which means 'indicating color or pigment.' Thus, chromosphere means 'sphere of color.'

What Are Spicules?

When you look at the structure of the chromosphere, it looks pretty ragged. It almost looks like a field has been set alight with fire. This ragged appearance is caused by spicules, jets of gas in the chromosphere of the sun. These spicules shoot upwards at about 50,000 miles per hour for about five to fifteen minutes before falling back down, and there are a good hundred thousand of them in the chromosphere at any given moment.

Such spicules are likely caused, in part, by magnetic fields in the sun, and they rise up around the edges of supergranules, kind of like grass rises up around the edge of a big rock in a field of grass. Supergranules are areas in the sun's photosphere where currents of gas rise and fall by way of convection.

Naturally, you would think these jets of gas are hot gas but, relatively speaking, they are actually cooler gas jets coming from lower parts of the atmosphere. That is to say, in the chromosphere, things are opposite -- with cooler lower regions and hotter upper regions.

Other than the spicules, there isn't much else to the chromospheric gas structurally. It's pretty empty as it's only about 10^-8 as dense as the Earth's atmosphere. Consequently, the chromosphere is ordinarily difficult to see because there's so little material in it, resulting in transparency at most visible wavelengths.

To get around this, astronomers can use a filtergram, a photograph of the sun made using light of a specific region of the spectrum.

Why the Pinkish-Red Color?

Unlike the photosphere (which has an absorption line spectrum), the chromosphere has a spectrum composed mainly of emission lines.

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