Helioseismology & the Heliosphere

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  • 0:02 Helio, the Sun
  • 0:54 Heliosphere & Heliopause
  • 1:20 Helioseismology
  • 4:06 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will go over important terms beginning with helio-: heliosphere, heliopause, and helioseismology - what they are and what importance helioseismology plays in our understanding of the sun.

Helio, the Sun

Helio-, a word referring to the sun, is a big part of this lesson's two-pronged analysis of concepts related to the sun.

The sun is more than just a light up in our sky. It is a musical instrument. It produces vibrations in a variety of frequencies, but we cannot hear this so-called music because those vibrations are too low-pitched for our mortal ears.

The sun is also more than just a ball of gas in our solar system. It is a wind generator, too. It produces the solar wind, an extension of the solar corona expanding into space, composed of a stream of atoms, ions, protons, and electrons flowing away from the sun at upwards of 1,000 kilometers per second.

These two concepts are related to helioseismology and the heliosphere, respectively, and are what this lesson is all about.

Heliosphere & Heliopause

The space affected by the solar wind is known as the heliosphere I just mentioned. It's like the space in a room affected by a little wind generator, a fan. Somewhere around 100 astronomical units from the sun it seems that the solar wind starts to blend into the interstellar gas. The boundary where the solar wind merges into the interstellar gas is known as the heliopause. From that point on, you're in interstellar space. This boundary is 121 astronomical units from the sun.


The solar wind that dominates the heliosphere is an extension of the outermost layer of the sun's atmosphere, the solar corona. The solar corona can be seen with the naked eye during a solar eclipse or with high-tech instruments. The other two layers of the sun's atmosphere, the chromosphere and the photosphere, can also be seen with high-tech instruments or with the naked eye, so long as eye protection is used.

But that's where we have to stop our visualization of the sun using visible light. Virtually no light comes up from below the photosphere, and therefore, we can't truly see inside the sun. So how do we study the solar interior then? Well, it's sort of like how we study the interior of the Earth. We can't see inside the Earth, but we can still find out a lot about it!

We do this for the sun via a technique called helioseismology, the study of the sun's interior by way of analysis of its vibrations. Remember, I told you before that the sun is like a musical instrument! The gas in the sun oscillates up and down in a wide variety of patterns, called modes of oscillation. A mode of oscillation is simply a specific pattern of vibration of the sun stemming from the convective movement of gas. Such vibrations are detected using Doppler shifts in the sun's surface. In essence, just like geologists study the Earth's interior by analyzing vibrations that occur thanks to earthquakes, astronomers can analyze the sun's interior thanks to helioseismology!

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