Scientists expose mystery behind northern lights
CAPE CANAVERAL, Fla. (AP) - July 25, 2008 On Thursday, NASA released findings that indicate magnetic
explosions about one-third of the way to the moon cause the
northern lights, or aurora borealis, to burst in spectacular shapes
and colors, and dance across the sky.
The findings should help scientists better understand the more
powerful but less common geomagnetic storms that can knock out
satellites, harm astronauts in orbit and disrupt power and
communications on Earth, scientists said.
A fleet of five small satellites, called Themis, observed the
beginning of a geomagnetic storm in February, while ground
observatories in Canada and Alaska recorded the brightening of the
northern lights. The southern lights - aurora australis - also
brightened and darted across the sky at the same time.
These auroral flare-ups occur every two or three days, on
average.
A team led by University of California, Los Angeles, scientist
Vassilis Angelopoulos confirmed that the observed storm about
80,000 miles from Earth was triggered by a phenomenon known as
magnetic reconnection. Every so often, the Earth's magnetic field
lines are stretched like rubber bands by solar energy, snap, are
thrown back to Earth and reconnect, in effect creating a short
circuit.
It's this stored-up energy that powers the northern and southern
lights or, in other words, causes them to dance, according to
Angelopoulos.
An opposing theory has these geomagnetic events occurring much
closer to Earth, about one-sixth of the way to the moon. More
Themis observations are needed to resolve the debate, said David
Sibeck, NASA's project scientist.
"Finally, we have the right instruments in the right place at
the right time, and it's allowed scientists to be able to make the
necessary observations to settle this heated debate once and for
all," said Nicola Fox, a Johns Hopkins University scientist who
was not involved in the study.
At present, about 20 of these geomagnetic storms are being
analyzed. Scientists hope to eventually learn, via this project,
more about the bigger solar storms that occur about 10 times a year
and can lead to far more expansive and prolonged northern and
southern lights.
The five Themis spacecraft - a NASA acronym standing for Time
History of Events and Macroscale Interations during Substorms -
were launched aboard a single rocket last year.
---
On the Net:
NASA: www.nasa.gov/themis