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Our Expert Voices conversation about the 2017 solar eclipse.

The solar corona — the outer atmosphere of the Sun that is revealed so spectacularly during a total solar eclipse — is one of the great mysteries in space science. The biggest puzzle of all is its extreme temperature of several million degrees. Why is the corona so hot when the solar surface below is a comparatively paltry 6,000 degrees?

Most solar physicists believe the primary source of the heat is stressed magnetic fields that permeate the corona and impulsively release pent up energy when the fields reach their breaking point. Occasionally this produces giant explosions called solar flares and coronal mass ejections. But much smaller nanoflares are happening all the time — about a million per second across the Sun — each equivalent to the detonation of a 50 megaton hydrogen bomb.

Why it matters: The corona produces large quantities of X-ray and ultra-violet radiation that are absorbed in Earth's upper atmosphere. Variations in radiation affect the propagation of radio signals, which adversely affects communication, navigation, surveillance, and precision weapons guidance systems. The upcoming solar eclipse affords us a rare view of the Sun's atmosphere and a chance to study how it gives rise to nanoflares so that we can improve space weather forecasts.

Other voices in the conversation:

Go deeper

Biden plans to ask public to wear masks for first 100 days in office

Joe Biden. Photo: Mark Makela/Gettu Images

President-elect Joe Biden and Vice President-elect Kamala Harris sat down with CNN on Thursday for their first joint interview since the election.

The big picture: In the hour-long segment, the twosome laid out plans for responding to the pandemic, jump-starting the economy and managing the transition of power, among other priorities.

The quick FCC fix that would get more students online

Illustration: Sarah Grillo/Axios

As the pandemic forces students out of school, broadband deployment programs aren't going to move fast enough to help families in immediate need of better internet access. But Democrats at the Federal Communications Commission say the incoming Biden administration could put a dent in that digital divide with one fast policy change.

State of play: An existing FCC program known as E-rate provides up to $4 billion for broadband at schools, but Republican FCC chairman Ajit Pai has resisted modifying the program during the pandemic to provide help connecting students at home.

Dion Rabouin, author of Markets
55 mins ago - Politics & Policy

America's hidden depression

Biden introduces his pick for Treasury secretary, Janet Yellen, on Dec. 1. Photo: Alex Wong/Getty Images

President-elect Biden faces a fragile recovery that could easily fall apart, as the economy remains in worse shape than most people think.

Why it matters: There is a recovery happening. But it's helping some people immensely and others not at all. And it's that second part that poses a massive risk to the Biden-Harris administration's chance of success.