The Sun

Our Sun is the nearest star to Earth
The Sun is the star at the center of the Solar System – almost perfectly spherical and
consists of hot plasma (gas) interwoven with magnetic fields.

The Sun

  • medium-sized and yellow star – measures 870,000 miles across and 109 times the diameter of the Earth in length.


  • it is made of gases – hydrogen and helium (the lightest gases in the Universe).
  • it weighs 2,000 trillion trillion tonnes – about 300,000 times as much as the Earth’s weight.
  • heating by nuclear reactions to  temperatures of 15 millionºC.
  • visible surface layer of our Sun is called photosphere – sea of boiling gas sends out the light and heat that we see and feel on Earth.


  • flames – it’s called spicules dart through a thin layer above the photosphere called the chromosphere.


  • above the chromosphere – the Sun’s halo `look-like` corona.
  • the heat from the Sun – erupts on the surface called granules or gigantic arcs of hot gases called solar prominence.

Solar Prominence


  • why our Sun gets hot? – because of so big and pressure inside the Sun; core is tremendous. (hydrogen atoms to fuse (join together) to make helium atoms, this nuclear fusion reaction is like nuclear bomb to release huge amounts of energy.

Nuclear Fusion Reaction

  • nuclear fusion reactions – five million tonnes of gas into energy every one second, but the energy takes ten million years to reach the surface.
  • the temperature of the Sun’s surface is 6,000ºC – each one centimeter square burns with the brightness of 250,000 candles.

Cutaway of our Sun with details

Cutaway of our Sun


Infrared photographs revealed the sunspots
that appear on the surface of our Sun.


  • dark spots on our Sun’s photosphere (surface) are called sunspots.
  • sunspots are 1500ºc cooler than the rest of the surface.
  • dark centre of the sunspot is the umbra – the coolest part of a sunspot, around the it is the lighter penumbra.

  • sunspots appears in groups that seem to move across the Sun over two weeks, as the Sun rotates.
  • small or individual sunspots may last less than one day.
  • number of sunspots reaches maximum every eleven years – this is called “Solar Cycle or Sunspots Cycle”. (see the video clip: Eleven years Solar Cycles)
  • next sunspots maximum will be around between 2019 and 2023.
  • when sunspots are at their maximum – the Earth’s weather may be warmer and stormier.

Sun’s eruptions

Solar flares are sudden eruptions on our Sun’s surface

Sun’s eruptions

  • eruptions could flare up in just few minutes, then take more than half hour to die away.
  • Sun’s flares reach temperature of 10 million degrees and have he energy of billions of nuclear explosions.
  • Sun’s flares send out heat and radiation – also streams of charged particles.
  • `Solar Wind` is the stream of charged particles that shoots out from our Sun in all directions at speeds of over one million miles per hour.
  • taking around three days to reach Earth from the Sun, but still blows far throughout our Solar System.
  • every second – Solar Wind carries away over one million tonnes of charged particles from our Sun.
  • Our Earth is shield from the lethal effects of the Solar Wind by its magnetic field.

Solar prominences

  • solar prominences are giant arcs of hot hydrogen (gas) that sometimes spout out from our Sun.
  • solar prominences reach temperatures of 10,000 degrees.
  • Coronal mass ejections are giant eruptions of charged particles from our Sun – creating gusts in the Solar Wind that set off magnetic storms on Earth.

Solar Wind

  • magnetic storms are massive hails of charged particles that hit earth every few years to set up the atmosphere buzzing with electricity.

Life cycle of our Sun

Life cycle of our Sun

  • the time frame of the Solar System’s formation has been determined using radiometric dating – Scientists estimate that the Solar System is over 4 billion years old.

Radiometric dating
(Click here for enlarge)

Our Sun

  • now our Sun around 4.6 billion years old – medium sized star, and halfway through its life.
  • probably live for other 11 billion years times.
  • after 11 billions years, our Solar System is gone.
  • over the next two or three, maybe four billion years, our Sun will brighten and swell until it is twice as bright and 50% bigger.
  • in 5 billion years, our Sun’s hydrogen fuel will have burnt out – inside our Sun’s core will start to shrink.

  • as its core shrinks – the rest of our Sun will swell up and its surface will become cooler and redder.
  • this will be a `Red Giant Star` that you can see compare other stars in our night skies today.
  • Our Earth will burn out long before our Sun is big enough to completely swallow it.

Example: Our Sun will end as a white dwarf.


Back to  The Solar System page / next to  The Planets  page.



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