Scientists Say: Corona

The sun’s outer atmosphere is so scorching it defies scientific explanation

multi-wavelength mosaic of the sun

There many ways to study the sun, as shown in this mosaic from NASA’s Solar Dynamics Observatory. Different slices of the sun in this image show how our star appears in different wavelengths of light. Studying the sun's light in all these different wavelengths may offer clues about why the star's outer atmosphere, or corona, is so hot.

NASA Goddard Space Flight Center

Corona (noun, “Koh-ROH-nuh”)

The corona is the outermost part of the sun’s atmosphere.

The sun’s visible surface is called its photosphere. Just above that lies a thin layer of the solar atmosphere called the chromosphere. And surrounding that is the corona — a wispy haze of charged gas, or plasma. The sun’s messy magnetic field tugs this plasma around in loops and streams that sway and snap.

About 13 million kilometers (8 million miles) from the sun’s surface, the corona shifts into the solar wind. This is a gust of plasma that continually wafts off the sun and through the solar system. The corona can also fling huge plumes of material into space. These high-energy bursts are known as coronal mass ejections. If thrown toward Earth, they can trigger auroras. They can also damage satellites and knock out power grids.

an illustration show the sun at the left, with loops of plasma swirling around its surface and some streams of it drifting off into space as the solar wind
Millions of kilometers (miles) away from the surface of the sun, the corona transitions into the solar wind — a breeze of plasma that flows out into the solar system.Lisa Poje/Goddard Space Flight Center/NASA

The sun’s corona is normally outshined by the bright disk of the sun’s surface. Scientists can use tools called coronagraphs to block out the sun’s disk and observe the corona. But those tools do not mask the sun’s surface perfectly. During a total solar eclipse, the moon does perfectly mask the sun’s disk, offering unique views of the corona fanning out around the sun like a crown. In fact, the word “corona” means “crown” in Latin.

One of the biggest mysteries about our sun is why the corona is so hot. The sun’s surface is only about 5,500° Celsius (9,940° Fahrenheit). But the corona is millions of degrees Celsius. Scientists suspect the sun’s magnetic field is involved in heating the corona. They just aren’t sure how.

In a sentence

Bursts of energy known as campfire flares might add heat to the sun’s corona.

Check out the full list of Scientists Say.

Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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