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Clear August 21 in your diary: It's a total solar eclipse for the smart

With apologies to Bonnie Tyler

Scientists are gearing up for the hotly anticipated total solar eclipse on August 21 by preparing a series of experiments.

The event, dubbed the Great American Eclipse, will blot out sunlight across a 70-mile (112-kilometre)-wide strip stretching from Oregon to South Carolina in the US. The last total solar eclipse visible coast to coast took place 99 years ago.

The eclipse will begin at Lincoln Beach, Oregon, at 9:05am PDT and make its way to Charleston, South Carolina, at 2:48pm EDT. Observers outside its path will see a partial eclipse: if you're in the UK, for example, you'll see a partial eclipse around 7.35pm BST on August 21.

Although the darkness will only last a few minutes, the total eclipse will provide a rare opportunity to study parts of the Sun that are not normally visible. The shadow will be cast when the Moon is wedged between the Sun and the Earth in a perfect line. The Moon will occlude the Sun’s light rays, making the wisps of hot plasma in the solar corona observable.

Scientists from the US National Science Foundation (NSF), NASA and the US National Center for Atmospheric Research, will try to understand why the corona is hotter than the Sun’s surface and the nature of coronal mass ejections.

The huge threads of plasma and magnetic field lines erupting from the Sun’s corona can be powerful enough to disrupt GPS systems.

An NCAR team will fly a Gulfstream-V aircraft to track the eclipse, increasing observation time. A team of scientists at the Southwest Research Institute, Colorado, United States will direct visible and infrared telescopes NASA’s WB-57 airplanes to inspect the solar corona and Mercury for eight minutes.

Boston University researchers will focus on how the solar eclipse affects Earth. The ionosphere is an area in the Earth’s outer atmosphere, where particles are ionized by incoming solar radiation and radio waves are carried.

GPS signals on mobile phones will be used as sensors to study how the radio signal varies as the level of solar radiation hitting Earth’s ionosphere falls during the eclipse.

Disturbances in the ionosphere can affect radio waves. Because the eclipse blocks energy from the sun, scientists can study the ionosphere's response to a sudden drop in solar radiation. In a similar experiment, scientists from Virginia Tech, the University of Virginia and George Mason University will analyze signals from radio transmitters broadcasting at low frequencies.

Observers will also be able to play a part. The US National Solar Observatory has launched the Citizen Continental-America Telescopic Eclipse Experiment, which relies on volunteers to use identical telescopes and cameras to observe the entire 93-minute eclipse.

Carrie Black, a program director working at the NSF in atmospheric and geospace sciences, said: “This total solar eclipse across the United States is a unique opportunity in modern times, enabling the entire country to be engaged through modern technology and social media. Images and data from as many as millions of people will be collected and analyzed by scientists for years to come." ®

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