The Sun

The Sun is the closest star, which makes life on Earth possible. The sun is a sphere with a 1.4 million km diameter (109 times as much as the earth’s diameter) and has a mass approximately 300.000 times greater than the earth’s mass. 75% of it is hydrogen, 23% is helium and only 2% is formed by heavier elements. It produces its heat by transforming hydrogen into helium in its inner core, where the temperature reaches 15 million °C (the surface temperature is around 6000°C). The transformation reaction is called nuclear fusion and joins together 4 nuclei of hydrogen (protons) to create a helium nucleus, freeing a large quantity of energy, which, as photons, is irradiated towards the space. A solar constant is the radiation that perpendicularly hits a unit surface positioned at the top limit of the atmosphere and amounts to 1350 watts per square metre. This heat, multiplied by the surface of the earth’s section (the squared earth’s average radius multiplied by pi Greco) calculates the quantity of energy the earth receives from the sun every second, i.e. 173,000 TW.

Special reports

  • 23 October 2013

    Carbon Footprint

    A very special footprint...

    13 May 2013

    Small steps, great footprints

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    22 May 2016

    Green chemistry

    Chemistry accompanies man from that day long ago...

  • 18 May 2011

    Artificial photosynthesis

    The history of science and technology is packed with discoveries and inventions inspired by nature...

    27 September 2012

    Over 7 billion people on Earth

    Demographers have estimated that on 31 October 2011 world population...

    18 January 2016

    Ten years of oil demand

    Eni has recently published the 14th edition of the 2015 World Oil and Gas Review...

  • 4 November 2009

    Ecological house

    At present, it is more and more difficult to assure the comfort standard...

    14 July 2021

    Italy’s renewable sources

    Renewable energy sources in Italy The Energy Services Operator (GSE) periodically publishes data and statistics on the renewable energy sources…

    10 September 2020

    A simple and ingenious invention

    There are objects so simple and ordinary that we forget their existence when we don't need them. Their presence is…

From the Multimedia section

Facts

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    Bio-climatic architecture

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