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At 2:50 Universal Time,
on July 23, 2012, the sun unleashed
an incredibly powerful coronal mass ejection, or
CME. A CME is a huge cloud of plasma
that bursts out of the sun's atmosphere and is held together with magnetic fields.
An average CME travels at about 1 million miles
per hour, and weighs around 2 trillion tons.
On this particular Monday, however, the sun unleashed a perfect
storm of plasma. Thanks to NASA's far-ranging
heliophysics fleet, we have an excellent picture of the event.
The incredibly high-resolution view of the sun,
provided by NASA's Solar Dynamics Observatory, or SDO,
revealed the beginning of the eruption in several different wavelengths of ultraviolet
light. [Music]
NASA's twin STEREO spacecraft, orbiting the sun ahead and behind
Earth, gave a similar view from alternate perspectives.
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The STEREO satellites also carry coronagraphs, which block the bright
solar disk, to make the fainter extended solar atmosphere, or corona,
visible. As a result, they were able
to image the actual CME as it left the sun.
The CME headed in the direction of the STEREO A spacecraft
at an astonishing 6.7 million miles an hour.
As the CME arrived at
STEREO A, the coronagraph and STEREO's wider-field
heliospheric imagers were pummeled by high-energy particles,
which appear like snow in the imagery. The joint ESA
and NASA Solar and Heliospheric Observatory, or SOHO,
that has been observing the sun since 1995,
captured footage of the CME in both of its coronagraphs, which overlap
their fields of view. All of these
data allow computer models to reconstruct the full shape and
expansion of the CME. The main event is preceded by
a few smaller CMES, one of which was Earth-directed.
It is immediately clear how much larger and faster
the July 23rd CME was, as it blasted towards
STEREO A. NASA's fleet of heliophysics
spacecraft, watching the sun from all sides, improves our understanding,
and enables predictions of these solar outbursts.
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