Solar eclipse and coronavirus: Why the Sun's corona shares its name with the virus

The August 12 total solar eclipse put the Sun's outer atmosphere in the spotlight as the Moon passed directly between the Sun and Earth, briefly blocking the Sun's bright disc. Along the path of totality, the darkness of the eclipse made one of the Sun's most striking features visible: the corona, a glowing outer layer that is usually difficult to see with the naked eye.

That might sound like a familiar word for anyone who remembers the coronavirus pandemic. And there is, in fact, a connection between the two. But it is a connection of language and appearance, not one of science.

The "corona" in the solar corona and the "corona" in coronavirus come from the same Latin word, referring to a crown or something crown-like.

What is the Sun's corona?

The solar corona is the outermost part of the Sun's atmosphere. It extends millions of kilometres into space and consists of extremely hot, electrically charged gas, or plasma. Despite being much hotter than the Sun's visible surface, the corona is normally difficult to see because the bright solar disc overwhelms its relatively faint light.

creates a rare natural opportunity to see it. When the Moon completely covers the Sun's bright surface during totality, the corona appears around the dark silhouette of the Moon as a glowing, uneven halo.

The word "corona" comes from Latin and means "crown" or "wreath". The name makes sense when looking at the solar corona during totality, when the Sun appears to have a luminous crown surrounding its darkened centre.

So what does this have to do with coronavirus?

The same word appears in "coronavirus" for a similar visual reason. Coronaviruses have spike proteins projecting from their surface. When coronavirus particles are viewed using an electron microscope, those projections create an appearance resembling a crown or halo around the virus.

That crown-like appearance is where the name "coronavirus" comes from. The virus family was named decades before COVID-19 emerged, and the term refers to the characteristic appearance of these viruses under a microscope.

So while the two uses of "corona" may seem surprisingly connected, there is no biological relationship between the Sun's corona and coronaviruses. One is a region of the Sun's atmosphere, while the other refers to a family of viruses.

Why the same word is used

The simplest way to understand the connection is to think of the word's original meaning. In both cases, scientists were describing something that looked like a crown.

During a total solar eclipse, the Sun's corona forms a luminous crown around the Moon's silhouette. Under an electron microscope, the spikes surrounding a coronavirus particle give it a crown-like appearance. The shared word comes from that visual resemblance.

So, the recent solar eclipse may have put the solar corona in view, while the coronavirus connection takes us in a completely different direction. The common thread is simply the ancient word "corona" and the crown-like appearance it was used to describe.