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THE
SUN is a huge, bright sphere of
mostly ionized gas about 5 billion years old. The closest star to Earth,
it is 145 million km The Sun is some 333,400 times more massive than Earth (mass= 1.99 x lO 30 kg), and contains 99.86% of the mass of the entire solar system. It is held together by gravitational attraction, producing immense pressure and temperature at its core (more than a billion times that of the atmosphere on Earth, and a density about 160 times that of water). At the core the temperature is 16 million degrees K, which is sufficient to sustain thermonuclear fusion reactions. The released energy prevents the collapse of the Sun and keeps it in gaseous form. The total energy radiated is 383 billion trillion kilowatts/ second, which is equivalent to that generated by 100 billion tons of TNT exploding each second. In addition to the
energy- producing solar core, the interior has two distinct regions: a
radiative and a convective zone. From the edge of the core outward, first
through the radiative and then through the convective zone, the
temperature decreases from 8 Because the Sun is gaseous, it rotates faster at the equator (26.8 days) than at the poles (as long as 35 days). The Sun's "surface," known as the photosphere, is just the visible 500 km- thick layer from which most of the Sun's radiation and light finally escapes, and is the place where sunspots are found. Above the photosphere lies the chromosphere (" sphere of color") that may be seen briefly during total solar eclipses as a reddish rim, caused by hot hydrogen atoms, around the Sun. Temperature steadily increases with altitude up to 50,000 K, while density drops to 100,000 times less than in the photosphere. Above the chromosphere lies the corona (" crown"), extending outward from the Sun in the form of the "solar wind" to the edge of the solar system. The corona is extremely hot millions of degrees Kelvin. The process that heats the corona is very mysterious and poorly understood, since the laws of thermodynamics state that heat energy flows from a hotter to a cooler place. Mysterious phenomena, such as this, are studied by researchers in NASA'S Space Physics Division.
Click on the images below for a larger one.
This image was
acquired from NASA's Skylab space station on December 19, 1973. It shows
one of the most spectacular solar flares ever recorded, lifting off from
the Sun.
This image of the
solar corona was acquired on 23 December 1996 by the LASCO instrument on
the SOHO spacecraft. It shows the inner streamer belt along the Sun's
equator, where the low latitude solar wind originates and is accelerated.
Over the polar regions, one sees the polar plumes all the way out to the
edge of the field of view.
"Plumes" of outward
flowing, hot gas in the Sun's atmosphere may be one source of the solar
"wind" of charged particles. These images, taken March 7, 1996, by the
Solar and Heliospheric Observatory (SOHO), show (top) magnetic fields on
the sun's surface near the south solar pole; (middle) an ultraviolet image
of the 1 million degree plumes from the same region; and (bottom) an
ultraviolet image of the "quiet" solar atmosphere closer to the surface.
This sequence of
images of the the Sun in ultraviolet light was taken by the Solar and
Heliospheric Observatory (SOHO) spacecraft on February 11, 1996. An
"eruptive prominence" or blob of 60,000°C gas, over 80,000 miles long, was
ejected at a speed of at least 15,000 miles per hour. The gaseous blob is
shown to the left in each image. Eruptions of this sort can produce major
disruptions in the near Earth environment, affecting communications,
navigation systems and even power grids.
A New Look at the Sun This image of 1,500,000°C
gas in the Sun's thin, outer atmosphere (corona) was taken March 13, 1996
by the Extreme Ultraviolet Imaging Telescope from the Solar and
Heliospheric Observatory (SOHO) spacecraft.
This is an X-ray image of
the Sun obtained on February 21, 1994. The brighter regions are sources of
increased X-ray emissions.
This image (left) shows the region around a sunspot. Notice the mottled appearance. This granulation is the result of turbulent eruptions of energy at the surface. (Courtesy National Solar Observatory/Sacramento Peak)
The parts of the Sun. This gives a basic overview of the Sun's parts. The three major interior zones are the core (the innermost part of the Sun where energy is generated by nuclear reactions), the radiative zone (where energy travels outward by radiation through about 70% of the Sun), and the convection zone (in which convection currents circulate the Sun's energy to the surface). The flare, sunspots and photosphere, chromosphere, and the prominence are all clipped from actual SOHO images of the Sun.
Most Recent SXT Composite Image Image Time :
26-NOV-00 02:47:35 UT This is a recent X-ray image of the sun, taken by the Soft X-ray Telescope (SXT) on board the Yohkoh satellite. The image is a composite of a long and short exposure for increased dynamic range. Prior to compositing, the component images are corrected for CCD dark current, straylight, and pointing.
STEREO, a two-year mission, launched October 2006, will provide a unique and revolutionary view of the Sun-Earth System. The two nearly identical observatories -- one ahead of Earth in its orbit, the other trailing behind -- will trace the flow of energy and matter from the Sun to Earth. They will reveal the 3D structure of coronal mass ejections; violent eruptions of matter from the sun that can disrupt satellites and power grids, and help us understand why they happen. STEREO will become a key addition to the fleet of space weather detection satellites by providing more accurate alerts for the arrival time of Earth-directed solar ejections with its unique side-viewing perspective. |
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The Future
Astronauts of America Foundation Title; 'We help launch the future' slogan;
Character and Name Ikky;
and
The Future Astronauts of America
Foundation Logo are
intellectual property of The Future Astronauts of America
Foundation
distant (this distance is called an
Astronomical Unit). The next closest star is 300,000 times further away.
There are prob- ably millions of similar stars in the Milky Way galaxy
(and even more galaxies in the Universe), but the Sun is the most
important to us because it supports life on Earth. It powers
photosynthesis in green plants and is ultimately the source of all food
and fossil fuel. The Sun's power causes the seasons, the climate, the
currents in the ocean, the circulation of the air, and the weather in the
atmosphere.
