The sun is a burning ball of gas at the centre of the solar system. It’s bigger than a million earths and has enough fuel to shine for five billion years. Its gravity holds the planets in place and its heat and light power life on earth. But the searing sun is a dangerous life-giver. One day, as it begins to die, the sun will reach out and consume the earth, and any life that still exists.

The sun was born around 4.6 billion years ago, as the swirling cloud of gas that formed the early solar system contracted due to gravity and heated up. Only part of the cloud formed the sun. The rest coalesced into the planets, comets and other bodies that spin around our nearest star.

Nuclear power
The sun is a yellow dwarf star, but don’t be misled by the name. At almost 1.4 million km (860,000 miles) across it’s 109 times wider than the earth - a mere speck in comparison. The surface sizzles at 5,500ºC (10,000ºF), but that’s not the hottest part. The ethereal corona, visible during an eclipse, flickers at several million degrees, while the core boils at over 15 millionºC (27 millionºF).

In 15 minutes the sun radiates as much energy to the earth as the world's population uses in a year.

Like most stars, the sun is made entirely of gas. Over 92 per cent of this is hydrogen, which is converted into helium by nuclear fusion deep inside the sun’s core. Every second, 500 million tonnes (600 million tons) of hydrogen is used to generate 386 billion megawatts of energy. In 15 minutes the sun radiates as much energy to the earth as the world’s population uses in a year.

Lethal rays
Sunlight and all other forms of electromagnetic radiation travel at 299,792km per second (186,282 miles per second). It takes only eight minutes to make the 150 million km (93 million miles) journey from the sun to the earth. About 60 per cent of this radiation is blocked by the planet’s atmosphere. Fortunately for life, this includes most ultraviolet rays, and all x-rays and gamma rays.

At the same time, earth’s magnetic field shields us from the solar wind - protons and electrons streaming from the sun at 400km per second (250 miles per second). Because parts of the sun rotate at different speeds, it too has a magnetic field. Its instability produces sunspots, looping jets of plasma and ferocious flares that can endanger astronauts, blind satellites and light up the sky with aurorae.

Source of life
Sunlight is used by green plants to create and store energy - a process called photosynthesis. It is the most important chemical reaction on earth, responsible for virtually all energy available for life in the biosphere.

Animals are not able to use sunlight in this way, and must get their energy from eating plants or other animals.

Death of a star
All stars eventually fade, but they go out with a bang. In a few billion years, the sun’s internal nuclear furnace will expand away from the exhausted core like a burning shell. When it bursts through the surface our sun will bloom into a red giant, vaporising the earth. Finally it will collapse back - a faint, cool shadow of its former glory.


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Main sources

NASA, ESA, Encyclopædia Britannica Online