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YOHKOH MISSION
CELEBRATES A DECADE OF SOLAR DISCOVERY
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| The
Changing Sun -- The 12 x-ray images of the Sun's atmosphere, obtained between
1991 and 1995 at 120 day increments, provide a dramatic view of how the corona
changes during the waning part of the solar cycle. |
| | The
intrepid Yohkoh spacecraft has been taking X-ray pictures of the Sun for more
than ten years, and is still going strong. More than six million Yohkoh "X-rays"
of the Sun are helping astronomers better understand the nearest star. The Japanese-led
international mission was launched August 30, 1991 from Kagoshima Space Center,
Japan. Astronomers are celebrating Yohkoh's tenth anniversary with a scientific
conference September 17 - 20 in Kona, Hawaii to discuss its latest discoveries.
"Yohkoh
was designed and flown to address the how, the why, and the where of high energy
processes on the Sun," said Dr. Loren W. Acton of Montana State University-Bozeman,
the US Principal Investigator for the Yohkoh Soft X-ray Telescope (SXT) instrument.
"It has succeeded beyond our original hopes and dreams in all of these areas.
The quality, coverage, and duration of Yohkoh data are unprecedented in a solar
space mission." NASA
TV will broadcast video of select Yohkoh observations September 10. Among
the many results from Yohkoh are discoveries about: -
The Sun's corona, including information about how and where this multi-million
degree outer layer of the Sun's atmosphere is heated to temperatures up to hundreds
of times greater than the solar surface. Yohkoh also tracked the dramatic year-to-year
evolution of the corona. -
The physics of solar flares, titanic explosions in the atmosphere of the Sun caused
by the violent release of magnetic energy. A typical solar flare can release in
less than one hour as much as 10,000 times the annual energy consumption of the
US. Yohkoh observations have helped astronomers understand better than ever before
how the Sun's magnetic fields are deformed and twisted, broken and reconnected
during flares; and how the electrified gas (plasma) of the Sun's corona is heated
to millions of degrees during flares. -
The structures that produce ejections of material from the Sun, helping astronomers
to understand and begin to predict "space weather". Although the prediction
tools are still rudimentary, two items of note along this line are the discoveries
that certain structures on the Sun, namely sigmoids and trans-equatorial interconnecting
loops (TILs), are more likely to be the sites of solar eruptions. The sigmoids
-- S-shaped regions seen in coronal imagery -- have been found to be more likely
to erupt than non-S-shaped regions. The TILs have recently received attention
as another possible source of mass ejections. Yohkoh
is the first spacecraft to continuously observe the Sun in X-rays over an entire
sunspot cycle, the roughly 11-year cycle in which the Sun goes from a period of
numerous intense storms and sunspots to a period of relative calm and then back
again. "The value of the Yohkoh observations increases as the mission continues
because they better reveal the many faces of our variable Sun," said Acton.
Additionally, the Yohkoh SXT carries the longest-operating Charge Coupled Device
(CCD) camera in space. After 10 years, the CCD camera -- similar in operation
to digital cameras now popular worldwide -- is still taking beautiful X-ray pictures
after collecting more than 6 million images. Yohkoh
is a mission of Japan's Institute of Space and Astronautical Sciences with the
cooperation of the United States and the United Kingdom. The US part is funded
by NASA; it comprises the building of the SXT by Lockheed-Martin Solar & Astrophysics
Laboratory (LMSAL), under the leadership of Dr. Acton. A consortium of organizations
is responsible for the science operations of SXT and the Yohkoh data analysis,
including LMSAL, Montana State University, Stanford University, and the University
of Hawaii. The
collaboration has been extremely fruitful, with more than 900 peer-reviewed publications
and 100 master's and doctoral theses to date. Yohkoh data are freely available
on-line for interested scientists worldwide, and are being analyzed in many countries,
including China, Saudi Arabia, India, Argentina, Brazil, Russia, Australia, most
European countries, and Canada. According
to the latest projections, Yohkoh will stay in orbit until the next solar maximum,
around 2010. In the coming years, Yohkoh will closely collaborate with the High
Energy Solar Spectroscopic Imager (HESSI), an upcoming NASA mission, providing
crucial calibration data for its high-resolution hard X-ray images. Solar-B is
the Japanese follow-up mission, again with involvement from the US and the UK.
It will look at the Sun in soft X-rays, as Yohkoh before, but it will also make
very high resolution images in visible light. Click
on links below for animations of Yohkoh's achievements:
THE
AMAZING CHANGING SUN
One of Yohkoh's main purposes is to study high-energy
solar flares to scrutinize where and how the energy is released and particle acceleration
takes place. This is a compilation of stills showing the complete solar sunspot
cycle as seen by Yohkoh from 1991 through 2001. The maximum point of the cycle
is regarded as 2000-2001. Yohkoh is a mission of NASA and the Japanese Institute
of Space and Astronautical Sciences (ISAS). TWO
YEARS OF SOLAR VIEWING
On a quiet day of few to no flares, Yohkoh's telescope
has been used to image the Sun's million-degree atmosphere to study how the hot
gases evolve, interact and change their magnetic structure on both small and global
scales. The result has been the discovery of new flaring phenomena and insight
into the heating and expansion of the high-temperature material.
THE
SPACECRAFT & LAUNCH
Yohkoh carries four instruments, each for observing
various kinds of X-rays depending on their wavelength or energy. Its Soft X-ray
Telescope (SXT) carries the longest-operating Charge Coupled Device (CCD) camera
in space, having shot over 6 million pictures. Launched on August 30, 1991, Yohkoh
is a Japanese Institute of Space and Astronautical Sciences mission with the cooperation
of the United States and the United Kingdom. Yohkoh will stay in orbit until the
next solar maximum, around 2010.
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