Our Expert Voices conversation about the 2017 solar eclipse.

The eclipse affords us the opportunity to study Earth's ionosphere, a layer of partially charged gas 90 - 1000 km above the surface that helps to transmit satellite and radio signals around the planet and to protect life here by absorbing the Sun's extreme ultraviolet radiation. Disruptions in the ionosphere — from space weather, for example — can interfere with communication and navigation. During the eclipse, we'll be able to measure how the ionosphere responds to a dramatic reduction of UV radiation (up to 85%) and therefore better understand the details of how the ionosphere works.

A prediction: Recent computer simulations of the upcoming total solar eclipse over the continental U.S. predict the density of electrons in the ionosphere will be reduced by 50%, their temperature will drop by 15%, and the wind structure of parts of the atmosphere will be disturbed. That should produce an effect that can be detected by GPS receivers as far away as South America — a prediction that will be tested during the upcoming eclipse.

The bottom line: The solar eclipse will allow us to answer key questions about Earth's space environment that may in turn ensure the accuracy of vital systems we use daily.

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Trump commutes Roger Stone's sentence

Roger Stone arriving at his sentencing hearing on Feb. 20. Photo: Drew Angerer/Getty Images

President Trump on Friday evening commuted the sentence of his longtime associate Roger Stone, according to two senior administration officials. Stone in February was sentenced to 40 months in prison for crimes including obstruction, witness tampering and making false statements to Congress.

Why it matters: The controversial move brings an abrupt end to the possibility of Stone spending time behind bars. He had been scheduled to report to prison on July 14.

Updated 10 hours ago - Health

Which states have set single-day coronavirus records this week

Data: COVID Tracking Project and state health department data compiled by Axios; Map: Danielle Alberti and Naema Ahmed/Axios

13 states this week surpassed records set just last week for their highest number of coronavirus infections in a single day, according to the COVID Tracking Project and state health department data. 16 states in total reported new highs.

The big picture: The United States' alarming rise in coronavirus cases isn't just due to increased testing — particularly where the number of cases has grown fastest over the last month, Axios' Andrew Witherspoon and Caitlin Owens report.

Updated 10 hours ago - Politics & Policy

Coronavirus dashboard

Illustration: Sarah Grillo/Axios

  1. Global: Total confirmed cases as of 6:30 p.m. ET: 12,389,660 — Total deaths: 557,279 — Total recoveries — 6,830,596Map.
  2. U.S.: Total confirmed cases as of 6:30 p.m. ET: 3,169,611 — Total deaths: 133,885 — Total recoveries: 983,185 — Total tested: 38,856,341Map.
  3. Public health: The reality of the coronavirus bites.
  4. Trade: Trump says he's no longer considering phase-two trade deal with China because the pandemic damaged the two countries' relationship.
  5. 🎧 Podcast: Rural America has its own coronavirus problem.