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Wednesday, July 5, 2017

Observe August’s Eclipse with an AM Radio

Solar eclipses are more than exceptional visual astronomical phenomena; they’re pretty interesting from a radio viewpoint too. Should it be cloudy over your location on eclipse day, you can still make some interesting observations using a basic AM radio.

Sudden changes can take place in radio reception when the day changes into night and vice versa. Perhaps you’ve had the experience of driving in your car at night, listening to some program on the AM dial, when the announcer will identify the station as WBBM in Chicago. This might seem odd if you are listening from Albany, New York, more than 700 miles (1,100 km) from the Windy City. Yet, cases like this happen every night.

At night, electrons in the ionosphere's F2 layer can refract radio waves broadcast by AM stations, allowing them to be picked up by receivers many hundreds of miles away. This schematic shows the ionosphere reflecting the waves, though actually, they refract along curved arcs when passing through the ionosphere. Adapted from Wikipedia Commons
At night, electrons in the ionosphere's F2 layer can refract radio waves broadcast by AM stations, allowing them to be picked up by receivers many hundreds of miles away. This schematic shows the ionosphere reflecting the waves, though actually, they refract along curved arcs when passing through the ionosphere. Adapted from Wikipedia Commons

A total solar eclipse produces an expansive, round area of darkness and greatly reduced sunlight that travels across Earth’s surface in a relatively narrow path during the daytime. Its effect on sunlight’s local intensity is remarkably similar to what happens at sunrise and sunset. Distant radio stations along and near to the path of totality might briefly experience enhanced propagation, thus making long-distance reception possible during a solar eclipse, unlike any other time.

We can thank Earth’s ionosphere for natural long-distance radio reception at night. The ionosphere is composed of a set of tenuous, electrically conductive layers that consist of both neutral and charged particles, extending from altitudes of approximately 30 miles (50 km) to more than 250 miles (400 km). The ions present in the ionosphere interact with radio waves in two ways. They can either absorb the waves, thus reducing their intensity and reducing signal strength, or they can refract the waves, changing their direction; conceptually this is akin to a radio-wave "mirror".

Read Full Source Article at http://www.skyandtelescope.com/2017-total-solar-eclipse/how-to-hear-the-solar-eclipse/

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