The Sun is now in the quietest phase of
its 11-year activity cycle, the solar minimum - in fact, it has been
unusually quiet this year - with over 200 days so far with no observed
sunspots. The solar wind has also dropped to its lowest levels in 50
years. Scientists are unsure of the significance of this unusual calm,
but are continually monitoring our closest star with an array of
telescopes and satellites. Seen below are some recent images of the Sun
in more active times.
A
sweeping prominence, a huge cloud of relatively cool dense plasma is
seen suspended in the Sun's hot, thin corona. At times, promineces can
erupt, escaping the Sun's atmosphere. Emission in this spectral line
shows the upper chromosphere at a temperature of about 60,000 degrees K
(over 100,000 degrees F). Every feature in the image traces magnetic
field structure. The hottest areas appear almost white, while the
darker red areas indicate cooler temperatures. (Courtesy of SOHO/EIT
consortium)
Detailed
closeup of magnetic structures on the Sun's surface, seen in the
H-alpha wavelength on August 22, 2003. (Swedish 1-m Solar Telescope
(SST) operated by the Royal Swedish Academy of Sciences, Oddbjorn
Engvold, Jun Elin Wiik, Luc Rouppe van der Voort) #
NASA's
STEREO satellite captured the first images ever of a collision between
a solar "hurricane", called a coronal mass ejection (CME), and a comet
on April 4, 2007. The collision caused the complete detachment of the
comet's plasma tail. Comets are icy leftovers from the solar system's
formation billions of years ago. They usually hang out in the cold,
distant regions of the solar system, but occasionally a gravitational
tug from a planet, another comet, or even a nearby star sends them into
the inner solar system. Once there, the sun's heat and radiation
vaporizes gas and dust from the comet, forming its tail. Comets
typically have two tails, one made of dust and a fainter one made of
electrically conducting gas, called plasma. (NASA/STEREO) #
Image
of an active solar region taken on July 24, 2002 near the eastern limb
of the Sun. The image highlights the three-dimensional nature of the
photosphere when seen at these large angles. The structures in the dark
sunspots in the upper central area of the image show distinct elevation
above the dark "floor" of the sunspot. The height of the structures has
been estimated by Dr. Bruce Lites of the High Altitude Observatory to
be between 200 and 450 km. The smallest resolvable features in the
image are about 70 km in size. There are also numerous bright "faculae"
visible on the edges of granules that face towards the observer. (Prof.
Goran Scharmer/Dr. Mats G. L�fdahl/Institute for Solar Physics of the
Royal Swedish Academy of Sciences)
The
total solar eclipse of February 16, 1980 was photographed from Palem,
India, by a research team from the High Altitude Observatory of the
National Center for Atmospheric Research. The photograph of the solar
corona was taken with a camera system developed by Gordon A. Newkirk,
Jr. This specialized instrument photographs the corona in red light,
6400 A -- through a radially graded filter that suppresses the bright
inner corona in order to show the much fainter streamers of the outer
corona in the same photograph. (Rhodes College, Memphis, Tennessee /
High Altitude Observatory (HAO), University Corporation for Atmospheric
Research (UCAR)) #
The planet Venus is seen by NASA's TRACE satellite, at the start of its transit across the sun on June 8, 2004. (NASA/TRACE) #
A
view of a sunspot and granules on the Sun's surface, seen in the
H-alpha wavelength on August 4, 2003. (Swedish 1-m Solar Telescope
(SST) operated by the Royal Swedish Academy of Sciences, G�ran Scharmer
and Kai Langhans, ISP) #
Solar
flares produce seismic waves in the Sun's interior that closely
resemble those created by earthquakes on our planet. On May 27, 1998,
researchers observed this flare-generated solar quake that contained
about 40,000 times the energy released in the great earthquake that
devastated San Francisco in 1906, equivalent to an 11.3 magnitude
earthquake, scientists calculated. Over the course of an hour, the
solar waves traveled for a distance equal to 10 Earth diameters before
fading into the fiery background of the Sun's photosphere. Unlike water
ripples that travel outward at a constant velocity, the solar waves
accelerated from an initial speed of 22,000 miles per hour to a maximum
of 250,000 miles per hour before disappearing. (Courtesy of SOHO/EIT
consortium. SOHO is a project of international cooperation between ESA
and NASA) #
An
animation of the sun, seen by NASA's Extreme ultraviolet Imaging
Telescope (EIT) over the course of 6 days, starting June 27, 2005.
(Courtesy of SOHO/EIT consortium) #
Hinode
(formerly known as Solar-B) successfully captured a massive solar flare
on 13 December 2006. It was one of the largest flares occurring in that
period of solar activity minimum. (JAXA/NASA/PPARC) #
The
image shows the corona for a moderately active Sun, with some (red) hot
active regions in both hemispheres, surrounded by the (blue/green)
cooler plasma of the quiet-Sun corona. Notice also the north
polar-crown filament, the trans-equatorial loops, and the coronal hole
in the south-east (lower-right) corner of the image and the smaller one
over the north pole. This image shows the solar corona in a
false-color, 3-layer composite: the blue, green, and red channels show
the 171�, 195�, and 284� wavelengths, respectively (most sensitive to
emission from 1, 1.5, and 2 million degree gases). (TRACE Project,
Stanford-Lockheed Institute for Space Research, NASA) #
A view of an irregular-shaped sunspot and granules on the Sun's surface, seen on August 22, 2003. (Swedish 1-m Solar Telescope (SST) operated by the Royal Swedish Academy of Sciences, Oddbjorn Engvold, Jun Elin Wiik, Luc Rouppe van der Voort, Oslo) #
On November 8, 2006, Mercury is seen, beginning a transit in front of the Sun. (NASA/TRACE) #
This
TRACE 171�-wavelength image from November 11, 2006 shows a sizeable
active region at the east limb of the Sun (rotated clockwise 90 degrees
so north is to the right) just as it rotates onto Earth-facing
hemisphere. Notice the low-lying dark structures of filaments at the
leading edge of the region, some "levitating" dark material on the
right-hand side of the region, and the small ephemeral region towards
the lower right. (NASA/TRACE) #
The
Sun, observed on May 22, 2008. With the Sun persisting in a
near-minimal state of activity, only a few small regions of some
activity are seen on the disk. The cell-like appearance is formed by
the multitude of small clusters of magnetic flux that are collected in
the downflow regions of the supergranular network of convective
motions. (NASA/TRACE) #
TRACE
171� image of an erupting solar filament above Active Region 9077 on
July 19, 2000. Filaments are concentrated bundles of magnetic field
filled with relatively cool gas, suspended in the solar corona. When
they become unstable, they can erupt, triggering coronal mass ejections
and solar flares. The dark material here is relatively cool, while the
bright material is hotter than a million degrees. As this hot material
cools, it condenses and drains down the lines of magnetic field in the
corona much like beads moving along a wire, a process some scientists
refer to as "coronal rain." (Caption courtesy Dan Seaton, Photo
courtesy Dick Shine, NASA/TRACE) #
This
LASCO C2 image, taken 8 January 2002, shows a widely spreading coronal
mass ejection (CME) as it blasts more than a billion tons of matter out
into space at millions of kilometers per hour. The C2 image was turned
90 degrees so that the blast seems to be pointing down. An EIT 304
Angstrom image from a different day was enlarged and superimposed on
the C2 image so that it filled the occulting disk for effect (Courtesy
of SOHO/LASCO consortium) #
Detailed
closeup of magnetic structures on the Sun's surface, seen in the
H-alpha wavelength on August 22, 2003. (Swedish 1-m Solar Telescope
(SST) operated by the Royal Swedish Academy of Sciences, Oddbjorn
Engvold, Jun Elin Wiik, Luc Rouppe van der Voort, Oslo) #
NASA's
STEREO (Ahead) spacecraft observed this visually stunning prominence
eruption on Sept. 29, 2008 in the 304 wavelength of extreme UV light.
It rose up and cascaded to the right over several hours, appearing
something like a flag unfurling, as it broke apart and headed into
space. The material observed is actually ionized Helium at about 60,000
degrees. Prominences are relatively cool clouds of gas suspended above
the Sun and controlled by magnetic forces. (NASA/STEREO) #
A
transit of the Moon across the face of the Sun on February 25, 2007 -
but not seen from Earth. This sight was visible only from the STEREO-B
spacecraft in its orbit about the sun, trailing behind the Earth.
NASA's STEREO mission consists of two spacecraft launched in October,
2006 to study solar storms. STEREO-B is currently about 1 million miles
from the Earth, 4.4 times farther away from the Moon than we are on
Earth. As the result, the Moon appears 4.4 times smaller than what we
are used to. (NASA/STEREO) #
On
September 30, 2001, TRACE observed an M1.0 flare in an active region
very near to the solar limb. Fragments of a prominence hovered above
the regions, with filamentary dark (relatively cool) material moving
along the field lines, which then spread to form this dragon-like
bright outline. (NASA/TRACE) #
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