The document discusses the sun's composition, structure, and its role in the solar system, highlighting that it is primarily made of hydrogen and helium and is responsible for the water cycle. It outlines the sun's internal processes, including energy generation through nuclear fusion and the regularity of solar radiation, while also noting the variability in solar emissions and solar spots. Additionally, it touches on the relationship between solar activity cycles and climate, specifically referencing historical periods of low solar activity coinciding with the little ice age.

1. Riccardo Rigon
IlSole,F.Lelong,2008,ValdiSella
Solar Radiation
The Sun

2. R. Rigon
The Sun is the origin of the water
cycle
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The Sun

3. R. Rigon
The Sun is mainly composed of hydrogen. The rest is prevalently He4.
Hydrogen is the fuel for the nuclear fusion that takes place inside the Sun and
produces helium. However, the He4 contained in the Sun for the most part
originates from previous stellar lives.
Composition of the Sun
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The Sun

4. R. Rigon
Sun Fact Sheet
The Sun is a G2 type star, one of the hundred billion stars of this type in our
galaxy (one of the hundred billion galaxies in the known universe).
Diameter: 1,390,000 km (the Earth: 12,742 km or 100 times smaller)
Mass: 1.1989 x 1030 kg (333,000 times the mass of the Earth)
Temperature: 5800 K (at the surface) 15,600,000 K (at the core)
The Sun contains 99.8% of the total mass of the Solar System (Jupiter
contains nearly all the rest).
Chemical composition:
Hydrogen 92.1%
Helium 7.8%
Other elements: 0.1%
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The Sun

5. R. Rigon
The Sun and the planets to scale
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The Sun

6. R. Rigon
The Sun’s energy is created in the core by fusing hydrogen into helium. This
energy is irradiated through the radiative layer, then transmitted by convection
through the convective layer, and, finally, radiated through the photosphere,
which is the part of the Sun that we see.
The internal structure of the Sun
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The Sun

7. R. Rigon
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The Sun
Provide a relatively constant rate of radiation energy that in few minutes
from the cromosphere arrives to the Earth.
DetailofaPellizzadaVolpedoPainting

8. R. Rigon
Solar Spots
Solar spots appear as dark spots on the surface of the Sun and they have a
temperature of 3,700 K (to be compared to the 5,800 K of the surrounding
photosphere). A solar spot can last for may days, the most persistent lasting for
many weeks.
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The Sun
Radiation flux is regular up to a point. In reality it manifests variations.

9. R. Rigon
An image of the sun in X-ray
band, taken by the Yohkoh solar
observatory satellite, which
shows changes in emissions of
the solar corona from a
maximum in 1991 (left) to a
minimum in 1995 (right).
Variability of the Emissions
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The Sun

10. R. Rigon
Solar radiation is subject to
fluctuations, some of which are
localised in restricted areas, while
others are more global and follow
an 11-year cycle.
Every 11 years the sun goes from
a limited number of solar spots
and flares to a maximum, and
vice versa. During this cycle the
Sun’s magnetic poles switch
orientation. The last solar
minimum was in 2006.
Variability of the Emissions
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The Sun

11. R. Rigon
The graph shows the solar spot cycle over the last 400 years. It should be
noted that before 1700 there was a period in which very few solar spots were
observed. This period coincides with the Little Ice Age, which is why there are
suggestions that there is a connection between solar spot activity and the
climate on Earth. The most evident cycle has a period of 11 years. But there
is a second cycle which seems to have a period of 55-57 years.
Variability of the Emissions
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The Sun