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The Sun
The sun is the largest object in the solar system, in both size and mass. It would take 109 earths lined up edge to edge to fit across
the sun, or almost 10 Jupiters. The sun is about 330,000 times more massive than earth and 1,048 times more massive than
Jupiter. In fact the sun contains more than 99% of all the mass in the solar system.
Therefore it controls the motions of the planets
and other objects in the solar system.
Inside the Sun
The sun consists of hydrogen, about 73.4% by mass, and helium, 25%, as well as a small amount of other elements. This composition is very similar to that of
gas giant planets, which suggests that the sun and the gas giants represent the composition of the interstellar
cloud from which the solar system formed.
Within the Sun’s core Fusion occurs. Hydrogen atoms are fused together to form helium atoms. The byproduct is an extreme
amount of energy in the form of heat and light.
The core (1) of the sun is around 27 million degrees F. The core also has a pressure 200 billion times that of earth. The sun is about 4.6 byo. At the sun’s rate of hydrogen fusing, it is about halfway through its lifetime,
with another 5 billion years or so left.
1
Above the core is the radiation zone (2). In this area gamma rays from the core are changed into x-
rays, ultraviolet, and visible light.
2
Next comes the convection zone (3) this is the zone that carries the energy the rest of the way to the
sun’s surface. It takes about 170,000 years to transfer energy to the surface of the sun through
these zones.
3
The Sun’s atmosphere
The lowest layer of the sun’s atmosphere or the surface of the sun is called the photosphere.
This is what we see. The photosphere is about 11,000
degrees F, the same as the core of the earth.
Above the photosphere is the chromosphere. Normally, this layer is only visible during solar eclipses. It is tens of thousands
degrees, but not hot/bright enough to see everyday.
The top layer is called the corona and extends several million kilometers from the top of the
chromosphere and has temperature range in the millions. Scientists still don’t understand why it is
hotter than the lower layers…
Sun’s Forces
The gas from the corona flows outward at high speeds and forms the solar wind. As this wind of
charged particles, or ions, flows outward through the entire solar system, it hits each planet in a flood of
particles.
At 1 AU, 93,000,000 miles, the distance earth is from the sun, solar winds can be measured at about 400 km/s. The
charged particles are deflected by the earth’s magnetic field and are trapped in two huge rings in earth’s
magnetic field. This is what causes the auroras.
Sunspots
The sun’s magnetic field disturbs the solar atmosphere periodically and causes new features to appear. The
obvious features are sunspots, which are dark spots on the surface of the photosphere.
The grainy appearance on the surface of the sun you saw in the previous slide is called granulation. The
granules are convection cells that can be as large as Texas.
Sunspots are actually very bright, but they appear darker than the surrounding area on the sun because they are cooler, around 7,400 degrees F. These are located in regions where the Sun’s intense magnetic fields poke
through the photosphere.
These magnetic fields prevent hot gases inside the sun from rising to the surface and heating the spots, making
them cooler. They typically last around two months.
•Astronomers have observed that the number of sunspots changes regularly and on average, reaches a maximum number every 11.2 years, then steadily declines.
•It is believed by some that this 11.2 year cycle causes subtle climate variations here on earth.
•Also, there were severe weather changes on earth during the latter half of the 1600’s when the solar activity cycle stopped and there were no sunspots for nearly 60 years. This time period was known as the “Little Ice Age” because the weather was very cold in North America and Europe.
Highly active solar flares are also associated with sunspots. These are violent eruptions of particles
and radiation from the surface of the sun.
Often, the released particles escape the surface of the sun in the solar wind and earth gets bombarded with
the particles a few days later. These particles can interfere with communications and damage satellites.
Prominence
Prominence is an arc of gas that is ejected
from the chromosphere, or gas that condenses in
the inner corona and rains back to the
surface. These can last from a few hours to a
few months. Like flares, prominences also are
associated with sunspots, and hence, occurrences of both vary with the solar
activity cycle.
