ARLA/CLUSTER: Efeito de um eclipse solar, a acontecer a 21 de Agosto, na propagação em Ondas Médias

[João Costa > CT1FBF]

'Observe' August 21 eclipse with your AM radio

Writing in Sky and Telescope meteorologist Joe Rao describes the
effect of a solar eclipse on radio propagation

Solar eclipses are more than remarkable visual astronomical phenomena;
they’re pretty interesting from a radio viewpoint too. Should overcast
skies prevail over your location on eclipse day, you can still make
some interesting observations using an AM radio.

Dramatic changes can take place in radio reception when 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.

A total solar eclipse produces a broad, 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.

Listening to distant radio signals is a most interesting hobby and is
referred to by amateur radio enthusiasts as “DX’ing.” As already
pointed out, radio signals in the commercial 540–1700 kHz AM radio
band can be heard for hundreds — sometimes even thousands — of miles
under the cover of darkness. This is especially true of the so-called
“clear channel” (Class A) radio stations. “Clear channels” are
frequencies set apart by international agreement for use primarily by
high-powered stations designed to cover wide areas with line-of sight
“groundwave” service and, at night, “skywave” service, particularly
for remote rural areas.

Read the full story at
http://www.skyandtelescope.com/2017-total-solar-eclipse/how-to-hear-the-solar-eclipse/

Joe Rao Weather
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