- explain how the Sun produces radiation
- distinguish between different regions in the cross-section of a star
- describe the granules on the surface of the Sun
Radiation is often given a bad reputation. It is a
term used when discussing harmful rays from the Sun or cancer
treatments. However, it isn’t always bad. Since radiation is actually
any energy emitted in the form of rays or waves, without it, life would
not be possible on Earth!
Particles from the corona travel away
from the Sun and stretch far out
mentioned in Unit 6, Lesson 1, the Sun produces radiation when
hydrogen fuses into helium, due to the high pressure and temperature in
the core of the star. Nuclear fusion occurs when light atoms combine to
form heavier atoms, releasing great amounts of energy in the process.
When small, light atoms combine to form heavier atoms, Did you know?
a great deal of energy is released.
getting a bad reputation comes from radioactive decay like what happens
with uranium, a radioactive material. With radioactivity, the nucleus
of the material is actually unstable in its present state and it
naturally splits, giving off smaller particles such as neutrons,
protons, or slightly larger clusters of both. These escaping particles
are also called radiation, specifically alpha rays and beta rays. As
well, this process sometimes releases gamma rays, which is a true form
of radiation: light.
Specifically, four hydrogen atoms combine to make
one helium atom. However, the mass of a helium nucleus is less than the
mass of the four hydrogen atoms which fused to create it. The extra
mass is converted into energy through the famous relationship E=mc2,
where m is the mass to be converted, and c is the speed of light. This
process occurs in all stars, including the Sun, which is composed of
about 90% hydrogen.
difference between one helium atom and four hydrogen atoms is a mere
0.000 000 000 004 Joules of energy (it takes about 36 000 Joules to run
a toaster for 30 seconds!). Though it may not seem like much,
converting just one gram of hydrogen into helium creates 350 000 000
000 000 000 000 000 000 000 000 000 Joules – over a billion billion
times the energy created in a hydrogen bomb!
main body of the Sun can then be divided into three sections, defined
by changes in the behaviour of the heat energy. As aforementioned,
fusion occurs in the core of the Sun. From there, the heat energy
pushes outward from the core in an effort to “float” to the surface. In
a sense, this is what stabilizes the star and prevents it from
collapsing inward due to intense gravitational pressures. The
temperature of the core of the Sun is about 15 000 000°C.
In the radiative zone
the energy from the nuclear reactions in the core continues to radiate
outward, traveling – more or less – in a straight line, until it
reaches the convective zone
the time the energy has reached this top 200 000km of the star, it has
cooled considerably. This difference in temperature causes convective motion
warm gas rises even closer toward the surface due to a lower density,
cools as it reaches the outer edge of the Sun and becomes more dense,
and then begins to fall back toward the core. As it falls, the gas
regains heat energy and begins to rise toward the surface again,
continuing the cycle. At the top of its motion, some heat is also
released into space, and eventually reaches us here on Earth.
The interior layers of the Sun. Try This!
a balloon to a medium size, and knot it. Place it in a freezer for a
few hours. What happens? As the air inside the balloon cools, it cannot
support the elasticity of the balloon, which loses its shape. Warming
up the balloon again will cause it to “re-inflate” as the hot air
pushes out from the centre of the balloon – just like the heat energy
pushes out from the centre of a star. Did You Know ?
it takes more than a million years for the energy to get from the core
of the Sun to the corona (leaving the Sun) because of the high density
of the Sun!
We can see evidence of convective motion in the granules
observed on the photosphere
(surface) of the Sun. Bright areas are the hot gas rising while the
dark areas surrounding the bright spots are the cool gas falling back
toward the centre. Each granule is between 1000km and 5000km in
diameter, and only lasts a few minutes before moving or changing shape,
due to the constant motion of the gas. The average temperature of the
photosphere is about 5700°C – still very hot, but certainly not as hot
as the core.
Up close, granules look like little bubbles on the surface of the Sun – and that’s exactly what
they are! Bright spots are hot, rising gas, while darker lines indicate cool, falling gas.