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What will happen when lights go out.

Byline: WITH DAVID WARRINGTON Stargazing

THE Sun that we see in the sky on a clear, bright day is a star.

It shines because it produces energy in its core and is extremely important for life here on Earth.

Stars form from enormous, dense, cold clouds of gas and dust that lie in the interstellar medium.

The interstellar medium, the vast space between the stars, is composed mainly of hydrogen and helium.

When older generations of stars came to the end of their life cycle, they shed heavier elements, made during the life of the star, into the interstellar medium.

Younger stars like the Sun contain some of these heavier elements. The Sun's mass is made up of about 71 per cent hydrogen, 27 per cent helium and one or two per cent of those heavier elements.

A trigger is often needed to make a gas cloud start to contract. This could be the gravitational pull of a passing star. It could be an immense density wave moving through the galaxy. Or it could be the huge shockwave produced from a supernova.

It could be that a nearby exploding star was the spark that led to a cloud contracting and the Sun forming 4.6 billion years ago.

As that gas cloud contracted, pressure and temperature shot up. At the centre of a clump of gas and dust, the heat and pressure would have been so great that nuclear fusion began. Nuclear fusion is the power plant process within all stars.

In the Sun, vast amounts of hydrogen atoms are fused together every second, changed into helium atoms producing massive amounts of energy. A star is born when nuclear fusion begins.

A star's life is something of a balancing act. Gravity is constantly trying to make the star contract. Radiation pressures within the star are trying to push it apart. When balanced and stable, the star is at hydrostatic equilibrium.

At this stable stage in a star's life cycle, it is known as a main sequence star and it will spend most of its life in this way. The Sun is currently a main sequence star, roughly halfway through its life, and will continue to fuse hydrogen in its core for about another five billion years.

Once the entire hydrogen fuel source in the core has been used up, the Sun will start to burn hydrogen all the way through its structure in a series of shells.

The Sun will expand and cool down, becoming a red giant, gradually using up all its hydrogen and leading to the eventual collapse of its structure.

It's not at all advisable to look directly at our nearest star the Sun (especially with binoculars or a telescope). But away from the glow of street lights, it is possible to see hundreds of stars at great distance with the naked eye on a clear night.

| David Warrington, FRAS, is resident astronomer at the Scottish Dark Sky Observatory in Dalmellington, Ayrshire. Find out more at www.scottishdarkskyobservatory.co.uk.

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Title Annotation:Features
Publication:Daily Record (Glasgow, Scotland)
Date:Sep 17, 2016
Words:519
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