The sun is the biggest star located at the centre of the Solar System. It is a near-perfect sphere of hot plasma believed to have a diameter of roughly 864,000 miles – 109 times the size of the Earth – and reaches temperatures of roughly 15,000,000C. The sun is by far the most important source of energy for life on Earth, with three-quarters of its mass consisting of hydrogen.
However, it will not live forever.
Eventually, hydrogen fusion in its core will diminish to the point at which the sun is no longer in hydrostatic equilibrium and its core will undergo a marked increase in density and temperature while its outer layers expand to eventually become a red giant.
Professor Brian Cox revealed during his BBC series “A Collection of Wonders” how scientists at the Paranal Observatory have predicted when this will happen – and it’s not good for life on Earth.
While visiting the observatory in the Atacama Desert, Chile, Professor Cox showed how they use four big telescopes to map out the lifespan of stars in our solar system.
He said in 2013: “Perched high above the clouds, four colossal instruments make up the European southern observatory’s Very Large Telescopes (VLT).
“Even with the naked eye, the scene here is spectacular.
“The first thing you notice is, streaking across the sky, the Milky Way.
“You can have no doubt when you look at it, that we live in a universe made up of billions of stars.”
Professor Cox went on to explain how the colour of a star reveals its age.
He added: “The next thing you notice, if you look very carefully, is that the stars aren’t just white beams of light – they are actually coloured.
“Astronomers have gazed upon a galaxy full of stars at all stages of their lives – from youthful bright stars, to middle-aged yellow stars like the sun.
“They meticulously charted the nearest 10,000 of them and arranged each one according to its colour and brightness.”
Professor Cox then explained how astronomers used something known as the Hertzspung–Russell diagram to predict the future of the sun.
This tool is a scatter plot of stars showing the relationship between the stars’ absolute magnitudes or luminosities versus their stellar classifications or effective temperatures.
He added: “What emerges is one of the most powerful and elegant tools in all of astrology – the Hertzspung-Russell diagram.
“This diagram allows astronomers to predict the history and evolution of stars and, in particular, their future life of or sun.
“The sun will spend most of its life on the main sequence, steadily burning its vast reserve of hydrogen fuel – which will last for at least another 5 billion years.
“Then its core will collapse, causing it outer layer to expand as Mercury is engulfed.
“It will grow to 200 times today’s size and our own planet’s prospects are dim.”