Most of the sunlight we
see from earth comes
from continuous
photosphere emissions.
These emissions make
up the “quiet sun”.
The active sun is sporadic,
unpredictable radiation.
It is characterized by
explosive outbursts,
but the active sun
contributes little to the total
light emitted by the sun.
Sunspots are dark
areas on the sun’s
surface. They
average 10 000 km
across (about the
size of earth).
Sunspots often
occur in groups;
the sun may have
100’s or more at
one time.
Sunspots have an
umbra, a dark center;
and a penumbra, a
grayish area around
the umbra.
Sunspots are cooler areas of
the photosphere.An umbra is
about 4500K, a penumbra is
about 5500K.
Sunspots seem dark because
they are seen next to hotter
regions of the sun’s surface;
about 6000K.
Sunspots change size
and shape, they may
fade out completely.
A spot may last from
1 to 100 days.
A group of spots
typically lasts 50 days.
Spots move across the
sun’s surface indicating
the sun’s rotation
speed. The sun exhibits
differential rotation, it
rotates faster at the
equator.
The photosphere
rotates once every
27 days at the
equator. It rotates
once every 31 days
at the poles.
Sunspots are sites
of concentrated
magnetic fields
(1000x the
undisturbed
photosphere regions).
They are the
strongest known
naturally occurring
magnets in the
solar system.
Sunspots may be
cooler because
fields block the
normal upward
convection of
the hot gases.
Sunspots almost always exist in
pairs with opposite polarity. All
the sunspot pairs in the northern
hemisphere have the same
polarity. In the southern
hemisphere all the pairs have
the opposite polarity of the
northern hemisphere.
Differential rotation
distorts the magnetic
field, wrapping it
around the equator.
Eventually it loops and
produces sunspot
pairs.
The solar cycle is a
pattern of increasing
and decreasing
numbers of sunspots.
Part of this is the
sunspot cycle.
Approximately every
11 years the sun has its
maximum number of
sunspots. Halfway
between these times of
maximum sunspots, there
are almost no sunspots.
The start of the cycle is
called solar minimum. Four
years into the cycle solar
maximum is reached. The
beginning of the next cycle
appears to overlap the
previous cycle.
The solar cycle is actually a 22
year cycle composed of
consecutive 11 year cycles.
These consecutive cycles have
opposite polarities of pairs of
sunspots. From one 11 year
cycle to the next the entire solar
magnetic field reverses itself.
Active regions are
areas of violent
eruptions around
sunspots. They tend to
be most violent around
solar maximum.
Prominences are loops
or sheets of glowing
gas ejected from an
active region. These
prominences move
through the inner
corona.
There are two basic
types of prominences:
The first is quiescent
prominences which are
suspended by the
magnetic field
and can persist
for days or weeks.
The other type of prominence
is an active prominence.
These come and go more
erratically; they may change
in hours. They are typically
some 100,000 km in extent
(10 times Earths’ diameter).
Flares are cataclysmic
explosions on the sun,
more violent than
prominences. They are
like bombs exploding in
the lower regions of the
sun’s atmosphere.
A flare can release as much
energy as a prominence, but it
can do so in hours rather than
days or weeks.
(The particles in a prominence
are held up by the sun’s
magnetic field; the particles in a
flare are blasted into space.)
At sunspot maximum,
the corona is an active
corona. It is more
irregular and extends
further out into space
than at sunspot
maximum.
The energy source of the sun
is fusion - light nuclei
combining to form heavier
nuclei.
Einstein’s theory of special
relativity explains where the
2
energy comes from: E = mc .
The extreme heat at
the center of the sun
7
(10 K) is needed to
force protons to
move fast enough
to fuse.
The basic equations
that occur inside the
sun are called the
proton-proton chain.
Step (1):
1 H
1
2
1H
+
1 H
1
-->
2
1H
+ positron
+ energy
+ 1 neutrino.
is a deuteron,
a positron is the
antiparticle of a proton,
A neutrino is a
massless chargeless
particle which can
pass through several
light years of lead.
Step (2):
A deuteron combines with
a proton to form a helium
nucleus:
2
1H
+
1 H
1
-->
3
2He
+ energy
Step (3):
3
2He
+
3
2He
4
-->
2He
+
1 H
1
+
1 H
1
+ energy
The net reaction is:
4
1 H
1
-->
4
2He
+ energy
+ 2 neutrinos
The energy is in the form
of gamma ray photons.
The same basic
process occurs
for all stars.
The number of
neutrinos given off by
the sun allows us to
determine if the solar
model is correct.
Unfortunately, every
measurement taken
shows less neutrinos
than expected.
This is the missing
solar neutrino
problem and has
three possible
solutions:
1. The sun
pulsates and
is now at a
low neutrino
emission level.
2. Neutrino oscillations neutrinos leave the sun at
the expected rate, but are
changed to some other
particle before detection.
(This is the most accepted
reason.)
3. Other materials
influence the internal
structure of the sun.
(In other words, the
solar model is wrong.)
In conclusion, the sun is
a mass of incandescent
gas, a gigantic nuclear
furnace where hydrogen
is changed into helium at
a temperature of millions
of degrees.
The sun is hot, the sun
is not a place where we
could live, but here on
earth there would be no
life without the light it
gives.