Cortesia del "National Solar Observatory/Sacramento Peak"

Il filmato mostra il brillamento solare del 7 aprile 1997. 
La durata reale dell'evento è di circa 2 ore e mezzo.

These images and movies shows a solar flare that occurred on the Sun on 7
April 1997 around 14:00 UT in active region 8027. The coronal mass ejection
that was observed coming toward the Earth on 7 April is thought to have been
associated with this solar flare. The movie runs from 13:35 UT through 16:10
UT and has one frame per about 4 minutes. The area shown is 82,000 miles by
54,000 miles in size. The images were taken at the Hilltop Dome at our
observatory (NSO/Sacramento Peak), using an H-alpha filter in front of the
camera.

The movie shows that the flare is of the two-ribbon kind, with brightening
in two ribbons that are mostly parallel. The dark and slender structure
between the two ribbons is a filament, which consists of material suspended
high above the visible surface of the Sun by magnetic field. Such a filament
usually indicates the position of the so-called neutral line that separates
the two kinds of magnetic polarity in the active region. A solar flare
occurs when strong magnetic field rearranges itself into a more relaxed
(less twisted) state. This process releases energy which heats up part of
the material. A solar flare results in temporary enhancement of radiation at
wavelengths including x-ray, ultraviolet, visible, and radio. The brightest
parts visible in the movie probably reached a temperature of about 20
million degrees Fahrenheit (10 million degrees Celsius), while the visible
surface of the Sun has a temperature of about 11,000 degrees F (6,000
degrees C).

Some of the energy may be used to shoot some material into outer space,
where it may pass by the Earth after a few days as part of the solar wind if
it happens to be going in the right direction. The Coronal Mass Ejection
observed by several instruments on the SoHO satellite just after the solar
flare was probably triggered by the solar flare.

These solar flares and coronal mass ejections look spectacular and are of
great interest to solar physicists (astronomers who study the Sun), but are
of no importance to the average person. There are usually a few solar flares
observed each day, even when we are near the minimum of the solar cycle, as
now. Near the maximum of the solar cycle large number of flares of the size
of this one or greater are observed: in 1989, for instance, about 3 solar
flares were observed each day that were at least as strong as the one
displayed here. As recently as 1 April 1997 a solar flare occurred that was
three times as strong (in peak x-ray brightness) as the one displayed here.

More images & Info

More images & info can be found at the following sites:

   * SoHO/EIT image of the coronal mass ejection in the Astronomy Picture of
     the Day for 11 April 1997.
   * Many images and movies of the event on the SoHO Latest News page.
   * The NASA press release about the event (number 97-67).
   * The Space Environment Center has much information about past and
     current events on the Sun and resulting circumstances in space near the
     Earth.
   * An explanation of the event (especially the cloud that reached the
     Earth) on the Eruption Page.
   * An explanation of the effects that the Sun has on the Earth, on the
     Polarity Page.
   * An explanation of sunspots and the solar cycle on the Sunspots Page of
     Mr Sunspot's Answer Book.

[LS 11 April 1997]
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Last Modified: 11 April 1997