Geoscience Reference
In-Depth Information
The sun, our nearest star
NEW DEVELOPMENTS
The sun is a nuclear furnace located about 150 M km away from our planet. Virtually all the energy reaching Earth
comes from the sun. Although the amount Earth receives is only some two billionth of the sun's total energy, it
provides sufficient heat to keep the planet within an equitable temperature range that allows life to thrive.
Solar energy is generated in the core by nuclear fusion where the temperatures are estimated to be near 15 M
s
C.
Hydrogen nuclei collide at very high speeds, fusing into helium nuclei and releasing vast amounts of energy. This
slowly makes its way towards the solar surface, from where it is released into space at temperatures of about 6,000
s
C.
The rotation of the sun under these conditions generates an intense magnetic field which in turn has an effect on
solar activity. Magnetic activity has a cycle lasting about eleven years. We can see evidence of this in the sunspots,
which are huge cooler regions dotted about the solar surface like black spots. Although the spots are cooler, they
are most abundant during the more active phases of the solar cycle, the surrounding areas radiating more energy
during these times, more than compensating for the darker sunspot areas. Satellite measurements of solar output
confirm that this is the case. At times of high solar activity, flares and prominences, consisting of vast jets of gas
arching into the solar atmosphere, can be ejected. They emit large quantities of energy and charged particles that
can reach Earth. As they disturb our magnetic field, there can be a great effect on radio and satellite communications.
The level of solar activity as measured by sunspots has been recorded for a considerable time (
Figure 9.10
).
During
the seventeenth century few sunspots were recorded, implying that solar activity was low. Recently the number of
sunspots has been much higher, associated with a more active sun. Global temperatures have increased during this
period and it has been argued that changes in solar activity have a significant effect on global temperatures. On
geological time scales the sun's output is believed to have risen steadily from values only about 80 per cent of present-
day ones about 4 Ga years ago.
Wavelength
(which involves disturbance of magnetic and electric
fields) is transmitted into the molecules making up the
ground and atmosphere, with a resulting change in the
type of energy.
Thermal energy can therefore be considered as energy
involved in the motion of extremely small components of
matter. The energy of motion is referred to as
kinetic
energy
(and thus thermal energy is sometimes described
as the kinetic energy of molecules). Any moving object
possesses kinetic energy, and it is through the use of this
energy that, for example, a stone thrown into a lake can
disturb the water and produce waves. It is also through
the exploitation of kinetic energy that turbines and
engines are able to produce heat, light and so on.
Chemical energy
represents a form of electrical energy
bound up within the chemical structure of any substance.
It is released in the form of thermal or kinetic energy when
the substance breaks down. Coal, when it is burnt, releases
heat. Food, when it is digested, provides the body with heat
and movement.
10
5
m
10
4
m
10
3
m
10
2
m
10 m
Long radio
waves
A
M radio broadcasts
FM radio
and TV
1 m
0.1m (100mm)
0.01m (10mm)
1mm
0.1mm (100
R
m)
0.01mm (10
R
m)
1
R
m
Microwaves
Infrared
radiation
Red
Orange
Yellow
Green
Blue
Violet
0.7
R
m
0.4
R
m
Visible light
Ultravio
l
et radiation
0.1
R
m
0.01
R
m
0.001
R
m
X rays
0.0001
R
m
Gamma rays
micrometre, one-millionth of a metre.
