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.
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.
