The Sun´s radiations
The Sun is our nearest star – a star like all other stars, and the source of energy for life on Earth. It is an enormous gas sphere nearly 4,5 billion years old. It is about 150 million km away (93 million miles), a distance which sunlight covers in approximately 8 minutes, whereas the distance to the Moon is only 1.3 light-seconds. This distance between Sun and Earth is also called 1 AU – one astronomic unit. |
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| General description of the Sun |
| The Sun is the largest body in our solar system, containing 99 % of the system’s mass. Its mass is constituted by ~ 75 % hydrogen and about 25 % helium, the two lightest of all elements. Other heavier gases contribute to less than 0,2 % of the solar mass. |
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| The solar furnace |
| Solar energy is produced in the Sun’s centre, where the temperature is very high. Because of this high temperature, a physical process called fusion takes place. The energy we now receive from the Sun was produced nearly one million years ago. |
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| Solar activity, electromagnetic radiations from the Sun |
| The electromagnetic radiation from the Sun is shown in the figure below. As this curve shows the transparency of our atmosphere is high in a broad window from UV to IR. |
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| The Solar Wind and Coronal Mass Ejections |
| Around 1960 the American Professor E. Parker suggested that the gas pressure in the corona could be large enough to force gas out into space – a wind of particles from the Sun with velocity of about 350 km/s. |
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| The solar magnetic field |
| The interior of the Sun below the photosphere is not directly observable in any spectral regions. Its outermost layer – called the convection layer, has a variable rotational period. |
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| The dynamic Sun |
| The Sun is our most important energy source, and has large direct and indirect influences on life and climate on Earth, as well as being the source of the aurora. The Sun’s electromagnetic and particularly its particle emissions are dynamics. |
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