AMAZING STRUCTURE OF THE SUN
Statistics on the Sun stretch the imagination. Sizes, distances and
temperatures are far beyond our experience.
diameter of the Sun is about 1,390,000 km. The
average diameter of the Earth is 12,740 km. About
109 Earths could be placed side-by-side along the
diameter of the Sun.
The volume of the Sun is unimaginable.
The volume is 1.406 x 1018 km3. Approximately 1,300,000
Earths could fit inside the Sun.
- Its mass is about 1.989 x 1030 kg. This is the
mass of about 300,000 Earths.
The structure of the Sun is separated into several regions:
Interior, Photosphere, Chromosphere, Transition Region, Corona, and
For a closer look at the Sun +
Website link for more.
Interior: The Core and the Radiative Layer
The core occupies the first 25% of the distance from
- The temperature at the core is enormous. The temperatures
range between 15,000,000°C (27,000,000°F)
at the center to 7,000,000°C (12,600,000°F)
at the outer edge of the core. This is very hot.
Metal that is hot enough to glow white is only around
- The density changes dramatically. It is 8 times
the density of gold (160g/cm3) at the center. At
the outer edge of the core the density is about the
density of gold (20g/cm3).
At these temperatures and pressures the hydrogen is fused into helium
and elements are in the plasma state. (For a FLASH
animation of this process visit +
website http://www.kingsu.ab.ca/ and
find the Proton-Proton Cycle).
Surrounding the core is the radiative zone.
- The radiation that escapes the core is mostly x-rays.
The Sun's energy output is about 4 x 1026 Watts of
energy. For comparison, the total U.S. demand for
electricity for 2001 was estimated at 6.7 x 105 Watts.
- According to Einstein's equation, E=mc2, this amount
of energy is equal to about 4.4 billion kilograms
of matter being completely changed to energy every
second. On Earth that amount of matter would
weigh about 1 million tons.
- This radiation takes about 1 million years to find
its way out of the radiative layer, even traveling
at the speed of light, due to collisions between
light and matter within the radiative layer.
Between the Radiative zone and the Convective zone is an Interface
layer. It is now believed that there is a magnetic
dynamo in this layer that generates the Sun's magnetic
field. (see also Why
Do Sunspots and CMEs Occur)
In the final 200,000 km (124,000mi.) to the Photosphere, energy is
carried by convection in the Convective zone.
- The temperature drops from 2,000,000°C (3,600,000°F)
to 5,700°C (10,000°F).
- The density drops from 0.2 g/cm3 to 0.0000002 g/cm3.
- Hot plasma rises and cooler plasma sinks, creating
'cyclones' as the Sun rotates.
As these bubbles of upwelling, hot plasma reach the surface of the Photosphere,
bright spots or granules are created.
The brighter spots are Solar granules and the large,
dark spots are Sunspots.
These granules and sunspots are features of the Photosphere
which is a thin layer only 100 km (62 miles) thick. We are most familiar
with this layer because it is the visible surface of the Sun. It produces
most of the white light we see.
Above the Photosphere is the Chromosphere. The temperature rises from about
6000°C (10,800°F) to about 20,000°C (36,000°F). At this temperature
hydrogen emits a reddish light. Solar flares and eruptions are common in
Between the Chromosphere and the Corona is a thin, irregular layer that is
poorly understood. This layer, called the Transition Region, is being examined
by TRACE (Transition Region And Coronal Explorer). Within this region the temperature
rapidly increases from 20,000°C to 1,000,000°C. Scientists are studying
this region to increase their understanding of the processes that cause this
Above the Chromosphere is the Corona. The temperature in the Corona is about
1,000,000°C (1,800,000°F). Hydrogen and other elements are ionized
and blown into space as a continuous outpouring of plasma known as the Solar
The image below captures a sweeping prominence as it
erupts from the Sun. Prominences are huge arcs of gas injected into
the corona. They can reach 200,000 to 300,000 km into the corona.
Prominences can be quite stable and last for days. When they erupt
they contribute additional energy to the solar wind. The Solar and
Heliospheric Observatory (SOHO) took the image below using the Extreme
ultraviolet Imaging Telescope (EIT). This instrument "looks" at
the Sun at four different wavelengths of light. All of these wavelengths
are in the ultraviolet region of the Electromagnetic
Spectrum. The four wavelengths in angstroms (10-8cm) are 304Å,
284Å, 195Å and 171Å. The image below shows the Sun
at 304Å. Emission in this wavelength shows the upper chromosphere
at a temperature of about 60,000ºC.
The hottest areas appear almost white, while the darker red areas
indicate cooler temperatures.
(Photo to left: Solar & Heliospheric Observatory (SOHO).
SOHO is a project of international cooperation between
ESA and NASA.)
Sometimes eruptions are very large and earn the name
Coronal Mass Ejection (CME). SOHO captured these images of a CME.
The central disk of the Sun is covered to screen the instrument from
the intense radiation of the Sun and allow the instrument to detect
the less intense
corona and CMEs.
The white circle shows the size of the Sun.
(Photo to right: SOHO/LASCO consortium.)
The bright white region coming from the central disk toward the right
is a Coronal Mass Ejection. The two, smaller white lines coming from
the bottom right are sun grazing comets that were quickly annihilated
by the heat of the Sun. Click on the link below the above image to
see a short movie of the CME and the comets.
Solar Wind and the more energetic Coronal Mass Ejections are extremely
important to the Earth and
to our life and society. It is time to learn more about the Solar
Wind and CMEs and Why
Sunspots and CMEs Occur.
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