Geoscience Reference
In-Depth Information
Figure 3.4 The elliptical Earth orbit.
As Earth travels on the plane of the eclip-
tic, it is closest to the Sun at perihelion
on January 3. Earth is farthest away from
the Sun at aphelion on July 4.
Plane of the
ecliptic
152 million km
(94.5 million mi)
147 million km
(91.5 million mi)
Aphelion
Perihelion
D i s c o v e r…
THE SUN
The Sun is easily the most important natural feature when it
comes to life on Earth. Although the Sun is about 100 times
larger than the Earth, it is quite small compared to the
millions of giant stars, multiple stars, pulsating stars, and
black holes scattered throughout the Universe. The Sun is
incredibly important for us because it provides the power
that drives most of the natural processes on Earth. This
power is generated because the Sun essentially functions
as a gargantuan nuclear reactor that converts hydrogen gas
to helium. As a result, the Sun's temperature is incredibly
high, ranging from about 15,000,000
o
C (27,000,000
o
F) at
the center to about 6000
o
C (10,800
o
F) at the surface. The
heat energy produced by these incredible temperatures is
the engine that powers Earth. Traveling at the speed of light,
it takes about 8 minutes for the Sun's energy to reach Earth.
In addition to emitting very high temperatures, the Sun
also produces strong magnetic fields. These fields cause
huge flares of hot gas to erupt from the surface in the shape
of loops, as shown here. The Sun also has cooler areas
scattered across its surface that appear dark in comparison
with the hotter and brighter background. These areas are
called sunspots. The number of sunspots at any one time
rises and falls in a regular cycle that is closely connected to
the Sun's magnetic field.
This image illustrates two interesting things about the
Sun.
First, notice how much bigger the Sun is than Earth, which
is the blue dot provided for scale. Second, look at the immense
size of the solar flare compared to the Sun. Such flares are loops
of gas that follow the pattern of the Sun's magnetic field.
Sunspots are cooler areas on the Sun that appear to be
relatively dark compared to the rest of the surface.
The
largest sunspot in this image is about the same size as Earth.
