Our Sun
Our Sun.
Our closest star is the strangest, most alien place in the Solar System.
It’s a place we can never hope to visit.
Through space exploration and a few chance discoveries,
our generation is getting to know the Sun in exquisite new detail.
For us it is everything.
Yet it is just one ordinary star among 200 billion starry wonders,
that makeup our Milky Way galaxy.
To explore the realm of our Sun requires a journey of over 13 billion kilometres.
This journey takes us from temperatures reaching 15 million degrees celsius,
in the heart of of our Sun, to the frozen edge of the Solar System,
where the Sun’s warmth has long disappeared.
In 2003, scientists discovered a dwarf planet at the remotest frontier of the Solar System.
Sedna is a planetoid three times more distant from the Sun than Neptune.
It is around 1600 kilometres in diameter.
Sedna is barely touched by the Sun’s warmth.
Its surface temperature never rises above -240 degrees celsius.
For most of its orbit, Sedna is further from our Sun than any other known planetoid.
To complete one orbit, which is a Sedna year, is twelve thousand earth years.
From it’s frozen surface 13 billion kilometres from Earth,
a view of the Sun rising would give a different perspective of our Solar System.
Sunrise on Sedna is no more than a rising star in the night sky.
From Sedna our blazing Sun is just another star.
Uranus was the first planet to be discovered with the use of a telescope,
in 1781, by William Herschel.
Like all giant planets, except Neptune, it is visible to the naked eye.
Even so, sunrise in Uranus is barely perceptible.
The sun hangs in the sky 300 times smaller than it appears on Earth.
We have to travel two and half billion kilometres past Jupiter and Saturn,
to arrive at the first world with the more familiar view of the Sun.
Over 200 million kilometres out, Sunset on Mars is a strangely familiar sight.
Twilight on Mars is a rather long affair, lasting for upto two hours before Sunrise,
and two hours after Sunset.
The reason for this slow progression to and from darkness,
is the fine dust that is whipped off the surface of Mars and lifted to incredibly high altitudes.
At this height, the Sun’s rays are scattered by the dust from the sunlit side of Mars,
around to the dark side.
This produces the long, leisurely and beautiful journey between day and night.
Here on Earth the most spectacular sunrise’s and sunsets,
are produced by a similar mechanism, when tiny dust grains are catapulted,
high into the atmosphere by powerful volcanoes,
scattering light into extra colourful moments on our Planet.
Earth is 150 million kilometres from the Sun.
Mercury is the closest planet to the Sun.
It is just 6 million kilometres from the Sun.
It spins so slowly that sunrise to sunset lasts for 176 Earth days.
Beyond it there is nothing but the naked Sun.
The Sun is a colossal fiery sphere burning with a core temperature,
of 15 million degrees celsius.
The sheer scale of the Sun is difficult to conceive.
It is 1,400,000 kilometres in diameter, which is over 100 times the diameter of the Earth.
This means you could fill the Sun with over a million Earths.
Its mass is 2 into 10 to the power of 30 kilograms.
This is 330,000 times that of our planet.
If we add up the masses of all the planets, dwarf planets, moons and asteroids,
they would contribute less than half percent of the Solar system.
The Sun is dominant, the rest is an after thought.
In 1838, John Herschel did a simple experiment,
to measure the amount of energy the Sun produces.
He calculated how much energy is delivered to a square metre of the surface of the Earth.
It turns out that on a clear day, when the sun is vertically overhead, it is about a kilowatt.
That equates to 10, 100watt bulbs being powered by the Sun’s energy,
for every metre square of the Earth’s surface.
With this number Herschel could take a leap of imagination,
and calculate the entire energy output of the Sun.
He knew the Earth is 150 billion kilometres away from the Sun.
He created an imaginary giant sphere around the Sun,
with the radius of 150 million kilometres.
By adding up each of the kilowatts for every square metre of this imaginary sphere,
he was able to estimate the total energy output of the Sun per second.
Every second the Sun produces 400 into 10 to the power of 24watts of power.
That is a million times the power consumption of the U S every year, radiated every second.
It is a wonder of the Sun, that it has managed,
to keep up this phenomenal rate of energy production for millennia.
Stars like the Sun are incredibly long lived and stable.
Our best estimate for the age of the Universe is 13.7 billion years.
The Sun is been around for nearly 5 billion years.
The Sun is originally a molecular cloud of dust and gas.
Over a period of 100,000 years, the cloud collapsed to become the Sun.
Molecular clouds are the raw material from which stars are made.
They are vast stellar nurseries that are among the coldest, most isolated places in the galaxy.
One example, of a molecular cloud that has been observed recently, is called Barnard 68.
It is about half a light year across.
It has a mass that is about twice that of our Sun.
Most importantly, it is incredibly cold.
In the heart of this cloud, the temperature is no more than 4 Kelvin,
that is -269 degrees Celsius .
The stability of a cloud like Barnard 68 is a fine balance.
On one hand the clumps of hydrogen and dust are moving around,
which leads to outward pressure that acts to expand the cloud.
Counter acting this is the force of gravity, an attractive force,
between all the particles in the cloud that tries to collapse it inwards.
In order for the cloud to become a star, gravity must gain the upper hand,
long enough to cause a dramatic collapse of the cloud.
This can happen only if the particles are moving very slowly, that is if the temperature is low.
Over millennia gravity’s weak influence dominates and the molecular cloud begins to collapse.
This forces the hydrogen and dust together in ever denser clumps.
The name for clumps of gas and dust collapsing under their own gravity, is protostars.
As the clouds collapse further and further they began to heat up.
Eventually in their cores they become hot enough,
for the hydrogen to begin to fuse into helium.
The star ignites, and the life cycle of a new star like our Sun has begun.
Nuclear fusion is the process by which all the chemical elements of the Universe,
other than hydrogen were produced.
There are just 3 fundamental building blocks of matter to makeup every thing,
from the most distant stars, to the smallest piece of dust in the Solar System.
Two kinds the Up and Down quarks, make up them the protons and neutrons,
in the atomic nuclei, and a third, the electrons, orbit around the nuclei to make atoms.
These particles make up literally everything.
The Universe is a complex, beautiful and diverse place with stars and planets.
Nuclear fusion is one of the primary process that built that complexity.
The Universe began 13.7 billion years ago in the Big Bang.
In the first instant it was unimaginably hot and dense.
It expanded and cooled very rapidly.
After just one second it was cold enough for the Up and Down quarks,
to stick together into protons and neutrons.
The hydrogen nucleus is the simplest in nature, comprising of a single proton.
Helium is the next simplest, built of two protons and one or two neutrons.
Then comes lithium, beryllium, boron, carbon, nitrogen, oxygen and so on.
Each of them has one more proton and accompanying neutrons.
This process of binding more and more protons and neutrons together,
is known as nuclear fusion.
The process of fusion is not easy.
Protons carry positive electric charge, which means that they feel a powerful repulsive force, when they get close
The force that drives them apart is one of the four fundamental forces of nature:
Electromagnetism.
If the protons get close enough, another force - called the strong nuclear force - takes over.
The strong nuclear force is aptly named - It is the strongest in the Universe -
and easily overcome the weaker electromagnetic repulsion.
We don’t notice the strong force in everyday life because its effects,
are felt over from very short range,
and it stays trapped when hidden within the atomic nucleus.
The way to get protons close enough for fusion to occur is to heat them up,
to very high temperatures.
Temperature is a measure of how fast things are moving around.
If the protons approach each other at a high speed,
it can overcome the electromagnetic repulsion and get close enough,
for the strong force to take over and bind them together.
For the first few moments in the life of the Universe, all of space was filled with particles,
that were hot enough to smash together and fuse.
This only lasted for a few minutes.
10 minutes after the Big Bang the Universe had cooled down enough for fusion to cease.
At that time our Cosmos was 75% hydrogen and 25% helium,
with very small traces of lithium.
Fusion did not reappear in the Universe until the first stars were born,
a few hundred million years later.
The high temperatures inside stars like our Sun mean that the hydrogen nuclei,
in their cores are moving fast for the electromagnetic repulsion to be overcome,
and the strong nuclear force to take over, initiating nuclear fusion.
The process is quiet complex and involved, and very very slow.
First two protons must approach each other to within 10 to the power of minus 15 metres.
Then something very rare must happen.
The proton must change into a neutron.
This happens through the action of a third of the four forces of nature :
the Weak Nuclear Force.
The Weak Force as its name suggests, unlikely to act.
An average proton will live for billions of years before the fusion begins.
When this first step towards fusion finally occurs,
a closely bound proton and neutron are formed.
This nucleus is known as Deuterium.
In the process, an anti-matter electron, known as a positron,
and a sub-atomic particle called a neutrino are released.
There is also important extra ingredient, which is the key to understanding why stars shine.
If you add up the mass of the Deuterium, the electron and the little neutrino,
you will find that it is slightly less than the mass of the original two protons.
Mass is lost in the fusion process and turned into energy.
This is an application of Einstein’s most famous equation : E=mc squared.
This energy emerges from the Sun as Sunshine.
It is the primary power source of all life on Earth.
The fusion process then proceeds much more quickly,
because the action of the Weak Nuclear Force is no longer required.
The positron bumps into an electron and disappears in another flash of energy.
A proton fuses with the Deuterium nucleus to make a form of helium known as helium 3,
which has two protons and one neutron.
Then two helium 3 nuclei fuse together to form helium 4,
which is the end product of fusion in the Sun, releasing two protons.
At each stage mass is converted into energy, keeping the Sun hot and shining brightly.
At the end of their life, stars run out of hydrogen fuel in their cores,
and more complex fusion reactions occur.
Heavier elements are produced - oxygen, carbon, hydrogen - the elements of life.
Every element in the Universe today was fused together,
from the primordial hydrogen and helium left over from the Big Bang.
Once photons leave the Sun, the journey to Earth is relatively short one.
Light like all forms of electromagnetic waves,
travel at the same speed of 300,000 kilometres per second.
So photon leaving the surface of the Sun will reach the Earth in about 8 minutes.
It would have travelled 150 million kilometres across space.
Each and every photon has a remarkable ability to shape and transform our planet.
For centuries it was assumed that the Sun, like all the heavens, was perfect and unchanging.
But gradually we have come to realise that the Sun is far more dynamic,
then just a perfect beautiful orb in the sky.
Even tiny fluctuations can have huge effects here on Earth.
As long ago as 28BC, Chinese astronomers, in the central Asia deserts,
had observed dark spots, on the surface of the Sun.
When the wind blew enough sand into the air to filter the Sun’s glare,
they could see strange spots, and recorded them in Chinese history books.
Over the next 1500 years, many others have recorded these dark spots,
on the surface of the Sun.
It was only after the invention of the telescope,
that Galileo was able to correctly explain the phenomena of sunspots.
The Solar and Heliosphere Observatory spacecraft,
or SOHO has taken images of the Sun in unprecedented detail.
It shows that birth, life, and death of the sunspot.
A sunspot can be bigger than the Earth.
Sunspots are transient events on the surface of the Sun,
that are caused by intense magnetic activity,
that inhibits the flow of heat from deep within the Sun upto to the surface.
These spots appear dark because they are dramatically cooler than the surrounding area.
They are often 2000 degrees celsius cooler.
In the 18th century it was thought that they might even be cool enough,
to allow humans to land on the surface of the sunspot.
But even these cool spots could have temperatures from 3000 to 4500 degree celsius.
This is enough to melt a spacecraft instantaneously.
Sunspots expand and contract as they move across the surface of the Sun.
They can be as large as 80000 kilometers in diameter.
Larger ones are visible without a telescope.
Advanced technology now allow us to track their numbers,
as they ebb and flow across the face of the Sun.
Since sunspots are cooler areas than on the rest of the Sun,
we might expect that the power of the Sun diminishes,
when the sunspot activity is at its height.
In fact we have found the opposite to be true.
The greater the number of sunspots, the more powerful our Sun become.
The variation is not random.
As we study the Sun in greater detail, we have began to observe patterns emerging.
These patterns seem to have direct links to our climate on Earth.
We have discovered that the Sun has seasons.
For decades scientists have sought to understand how the seasons of the Sun,
might be affecting the Earth.
It is a puzzle that led to one man to look away from the Sun,
and focus instead on the rivers around the Iguacu falls.
The Iguana river stretches for over 1000 kilometres.
It eventually flows into the Parana, one of the great rivers of the world.
It is these river sisters that eventually drained all the rainfall,
from the southern Amazonian basin into the Atlantic.
Billions of gallons of water flow through the river system each day.
Moisture from the pacific ocean is carried by clouds over the Andes,
and into the continental interior by the energy of the Sun.
The Argentinean astrophysicist Pablo Mauas has spent a decade analysing data,
that details every aspect of the river system, from water levels to flow rates.
He has done this from 1904 through the 20th century.
Unlike many of the world’s great rivers, the Parana is so large,
that it can be navigated by very big ships.
When there are ships, there are records.
These records enabled Pablo to uncover an extraordinary history, and to reveal that,
just like sunspots, the river too has a rhythm.
He found that the stream flow of the river fluctuated dramatically,
3 times during the last century.
But the records gave no indication of the reason behind the fluctuations.
We have known for over 150 years that the Sun follows a cycle,
that is repeated every 11 years.
The cycle reflects a rhythm variation in the number of sunspots.
This gives a clear indication of the radiation given by the Sun.
The greater the number of sunspots, the greater the energy reaching the Earth.
Pablo could not find a link between the Parana’s rhythm and the Sun’s 11 year cycle.
He studied the underlying brightness of the Sun, during the last century.
We know that climate change and events such as El Nino can boost the flow of the river.
When Pablo removed both these effects from the data,
there appeared to be a strong relationship between the solar data and the stream flow.
When the solar activity rises, the volume of water in the river goes up.
There is a beautiful correlation between the flow of these rivers and the solar output.
Changes in the Sun seems to affect weather systems in other places also.
In India, the monsoon appears to follow a pattern boosting precipitation,
when solar activity is at its greatest.
In the Sahara the opposite seems to occur : more solar activity means less rain.
The exact mechanisms by which our Sun may affect Earth’s weather remain,
for now, a mystery.
We know that the energy production of the Sun,
the power released in the fusion reactions at the core, is very constant.
So the changes we see must be to do with the way in which energy exits the Sun.
The amount of variation that falls on to the surface of the Earth is only .1%.
Yet it really does reveal the intimacy and delicacy of the connection,
between the Sun and the Earth.
The Sun is the source of energy for almost all of life on Earth.
Every plant, algae and many species of bacteria rely on the process of photosynthesis,
to create their own food, using the power of the Sun.
This in turn creates the foundation for the complex web of life on Earth.
The process of photosynthesis maintains the normal level of oxygen in the atmosphere.
It also is the basis on which almost all life depends for its source of energy.
We are just beginning to understand the complex mechanisms,
by which plants capture sunlight.
Some of the explanations may take us off into the quantum world.
But at its most basic chemical level photosynthesis is a simple process.
Inside every leaf are millions of organelles called chloroplasts.
Its these chloroplasts which do something magical when they capture a photon,
that has taken a eight minute, 150 million kilometre journey from the Sun.
The chloroplasts take in carbon dioxide and water, and by capturing the energy from sunlight, they convert it into oxygen and complex sugars or carbohydrates.
It is these carbohydrates that are the basis of all food we eat.
The amount of energy trapped by photosynthesis is immense.
It is about 100 terawatts years, which is six times larger,
than the power consumption of human civilisation.
Plants have evolved to use just a fraction of the sunlight that is received by Earth.
Sunlight is made up of all the colours of the rainbow.
Different wavelengths of light have different colours.
Blues have the shortest wavelength, and reds have the longest wavelength.
The red, green and blue photons have very specific characteristics.
The red photons don’t carry much energy, but there are less of them.
The blue photons are fewer, carry a little more energy.
Plants have evolved to gain the maximum energy most efficiently.
Plants use only the ones from the red and blue bit of the spectrum.
The intricate relationship between the evolution of plants and our Sun,
has had a profound effect on one of the defining features of our planet.
When a red or blue photon hits a plant, it is absorbed,
so those wavelengths of light do not bounce back into your eye.
When a green photon hits a plant, it is reflected.
This green wavelength of light bounces off a leaf into the eye, to create a living world,
that is defined by one colour more than any other: green.
The verdancy of forests that cover our planet, is all down to how plants have adopted,
to the quality of the Sun’s light.
From 150 million kilometres away the Sun looks like a perfect disc.
It is in fact closer to a perfect sphere than any planet on moon in the solar system.
It measures half a million kilometres across.
Its variation from top to bottom and side to side is little more than 10 kilometres.
This near perfection belies the incredible complexity of the structure.
It is composed mostly of the two simplest elements of the Universe, hydrogen and helium.
Hydrogen makes up about 3 quarters of the mass of the Sun,
with helium making up a quarter.
Less than 2% consists of heavier elements like iron, oxygen, carbon, and neon.
The Sun is 330,000 times as massive as Earth.
It is neither gas, liquid or solid.
It is in the fourth state of matter known as plasma.
Plasma is a gas in which a large proportion of the atoms,
have had their orbiting electrons removed.
This happens because the temperature is high enough to strip the atomic nuclei,
of their electrons.
Plasmas are the most common state of matter in the Universe.
In Earth fluorescent light bulbs are filled with glowing plasma when they are illuminated.
Because plasmas contain a high proportion of naked, positively charged atomic nuclei,
and free negatively charged electrons.
They are electrically conductive and so hugely responsive to magnetic fields.
This gives the Sun a whole host of strange characteristics that are not found,
on any other body in the solar system.
It rotates faster at its equator than at its poles.
One rotation takes 25 days at the equator, and 30 days at the poles.
150 times denser than water and reaching temperatures of upto 15 million degrees celsius,
the core of the Sun is a baffling and bewildering structure.
It is where the Sun’s fusion reactions occur, which generates 99% of its energy outputs.
600 million tonnes of hydrogen are fused together every second,
creating 596 million tonnes of helium.
The missing four million tonnes is converted into energy.
This is the equivalent of 90 billion megatons of exploding TNT.
This energy is transported to the surface by high energy photons or gamma rays,
released in the fusion reaction.
The life of a newly created photon in the core of the Sun is not a simple one.
Most are quickly absorbed with in a few millimetres of their point of creation,
by the dense plasma of the core.
They are then re-emitted in random directions.
The journey of the gamma ray from the core of the Sun, to the surface is like a very hot,
very long and very unpredictable game of pinball.
This results in the release of millions of lower energy photons at the Sun’s surface.
All the light that reaches here on Earth is incredibly ancient.
It is estimated that a single photon can take anywhere from 10,000 to 170,000 years,
to make the journey from the Sun’s core to the surface,
before it can make the 8 minute journey to Earth.
By the time a photon reaches the surface, or photosphere,
the Sun’s temperature has dropped from 13 million degree celsius to 6000 degrees celsius.
It is this massive change in temperature that causes the vast convection currents,
that swirl through the Sun.
This creates thermal columns that carry hot material to the surface,
and create its characteristic granular appearance we see from Earth.
Beyond the surface of the Sun is the strange and invisible layer,
known as the solar atmosphere.
This is visible to the naked eye on Earth during a total solar eclipse.
The Sun’s atmosphere is made up of a thin collection of electrically charged particles,
protons and electrons.
The atmosphere of the Sun cools as you get further away from the surface.
At a distance of 500 kilometres is an area known as Temperature Minimum,
which has a temperature of 4400 degree celsius .
This location is the coolest area of our Sun,
and the first place in which we can find simple molecules like water and carbon dioxide,
surviving in close proximity to the Sun.
Beyond this region something odd happens.
As you move further away from the Sun, the atmosphere doesn’t get cooler,
it gets dramatically hotter.
The outer region of the Sun’s atmosphere is known as the corona.
This mysterious layer of the Sun becomes visible to the naked eye during a total solar eclipse.
The corona is larger and hotter than the Sun itself.
It stretches out more than 1 million kilometres from its surface,
With an average temperature of a million degrees celsius.
Some areas reach colossal temperatures of upto 20 million degrees celsius,
which is hotter than the core of the Sun.
The mechanisms that drive the corona to these high temperatures are not yet fully understood.
This effect is certainly due to the complex magnetic interactions,
that occur between the surface and the corona.
What is known is that each and every day, at the very top of the atmosphere,
some of the most energetic coronal particles are escaping.
The Sun leaks 7 billion tonnes of corona every hour into space.
This is a vast superheated, supersonic collection of smashed atoms,
that en masse are known as the solar wind.
This is the beginning of a epic journey that will see the Sun’s breath,
reach the furthest parts of the solar system.
This creates the final vast structure of our Sun - the heliosphere.
In 1858, Carrington made the first observation of an event,
that would eventually become known as a solar flare.
The massive explosion in the Sun’s atmosphere releases a huge amount of energy.
Carrington noticed that this event was followed by a geomagnetic storm,
a massive destruction of the Earth’s magnetic field, the day after the eruption.
Carrington was the first to suspect the two events might be connected.
Beyond the weather in our atmosphere,
the solar wind creates another more tenuous atmosphere,
and weather system that surrounds our planet.
We rarely notice this ethereal weather high above us,
because by the time the solar wind reaches Earth its pretty diluted.
If you went into space close to the earth and held up your hand, you wouldn’t feel a thing.
In fact, they are five protons and five electrons for every sugar cube’s worth of space.
They are travelling very fast, carrying a lot of energy,
- enough to severely damage our planet’s atmosphere,
were it not for a defence system generated deep within the Earth’s core.
On a sunny winter day in the Artic, it’s hard to imagine that our Sun could be a threat.
Yet high above us deadly solar particle stream our way,
at speeds topping a million kilometres an hour, and bombard the Earth.
On the surface we are protected from the intense solar wind,
by a natural shield that deflects most of it around us.
This is the Earth’s magnetic field, an invisible shell that surrounds the planet,
in a protective cocoon.
The magnetic field emanates from deep within our planet’s spinning iron rich core.
It is this gigantic force field, known as the magnetosphere,
that deflects most of the lethal solar wind harmlessly away into space.
However the planet doesn’t escape completely.
When the solar wind hits the Earth’s magnetic field, it distorts it.
It stretches the field out on the night side of the planet.
In some way it is like stretching a piece of elastic.
More and more energy goes into the field, and overtime the energy builds up.
This stretches the tail until it no longer hold on to it all.
Eventually the energy is released,
accelerating a stream of electrical charged particles down the magnetic field lines,
towards the poles.
When these particles, energised by the solar wind, hits the Earth’s atmosphere,
they create one of the beautiful sights in nature: the aurora borealis or Northern lights.
In the autumn of 1977, a pair of identical 722 kilogram space craft were launched from Florida.
Voyagers 1 and 2 were about to embark on a very special mission,
to visit all four of the solar systems gas giants - Jupiter, Saturn, Uranus, and Neptune.
Normally, such a journey would take 30 years to complete.
By a stroke of good fortune, these spacecraft were designed at a time,
when the planets were uniquely aligned.
This allowed the spacecraft to complete their grand tour in less than 12 years.
After 40 years of their launch both spacecrafts are alive and well.
Voyager 1 is still reporting back to Earth.
It is currently the furthest man-made object from Earth.
Travelling at 17 kilometres per second, this extraordinary spacecraft,
is over 17 billion kilometres from Earth.
It is delivering knowledge that it was never designed or expected to uncover.
Listening to voyager 1 is the sensitive ear of Goldstone Mars station,
in the Mojave desert, California.
It is one of the few telescopes which is capable of communicating over such vast distances.
Voyager is so far away that it takes the signal 15 hours to arrive,
travelling at the speed of light.
The information voyager is sending is providing the first data from the edge of the heliosphere.
It is constantly measuring the solar wind as it fades away.
Voyager 1 has reached a point where the wind that emanated so powerfully from the Sun,
has literally run out of steam.
The heliopause is the boundary at which the solar wind,
is no longer strong enough to push against the stellar wind of the surrounding stars.
Beyond this point it will leave the solar system and head off into inter stellar space.
Update : In May 2024 Voyager 1, had left the heliosphere, and was in interstellar space,
at a distance of 24.3 billion kilometres away.
The Sun’s empire doesn’t end at this distant frontier, seventeen billion kilometres away,
when the solar wind needs the interstellar wind.
The Sun has the final, invisible force that reaches out much further.
The Sun makes up 99% of the solar system’s mass.
It is this immensity that gives the Sun its furthest reaching influence - gravity.
This is the full extent of the Sun’s empire.
A light gravitational force retains a cloud of ice, that encloses the Sun in a colossal sphere.
This cloud is called the Oort cloud, which is one light year away.
Beyond the Oort cloud there is nothing.
Only sunlight escapes.
This sunlight will take four years to reach the nearest star - Proxima Centauri.
Proxima Centauri is a red dwarf.
It is one among the 200 billion stars that makeup all the milky way.
It is by looking here deep into our local galactic neighbourhood,
that we are learning to read our Sun’s ultimate fate.
The Sun’s empire is so vast and so ancient, and its power so immense,
that it seems an audacious thought to imagine,
that we could comprehend that the death of our Sun.
Astronomers at the Paranal Observatory in Chile, are looking for these answers,
using some if the most powerful array of telescopes, called Very Large Telescope or VLT.
Through this telescope we can see stars in different colours,
like orange-red, yellow, blue-white.
We can observe stars in different stages of their lives,
from youthful bright stars to middle aged yellow stars, similar to the Sun.
The colours allow us to compute the life cycle of the star.
For the last 100 years astronomers have meticulously charted the nearest 10000 stars,
and arranged each according to their colour and brightness.
From this was born the Hertzsprung-Russel diagram.
It is a powerful and elegant tool to predict the history and evolution of stars,
and in particular the future life of our Sun.
Most of the stars, including our Sun are found in the main sequence,
the band of stars that runs from the top left to the bottom right.
The Sun will spend most of its life there.
It will steadily burn its vast reserve of hydrogen fuel,
which will last for another five billion years.
After which, it will pass through a Red Giant Phase.
Eventually like all stars, Sun’s fuel will run out.
Its core will collapse and our Sun will begin its last journey.
There is a final remarkable twist to our Sun’s 10 billion year story.
When the fuel does finally run out, the nuclear fusion reactions in the Sun’s core,
will grind to a halt.
Gravity will be the master of our Sun’s fate once more.
The Sun will no longer be able to support its own weight, and it will begin to collapse.
Just as in its formation, this collapse will start to heat the Sun once more,
until the layers of plasma outside the core become hot enough for fusion to begin again.
This time on a much bigger scale.
Our Sun’s brightness will increase by a factor of 1000 or more.
This will cause it to swell to many times it’s current size.
The Sun will drift off the main sequence and into the top right hand side,
of the Hertzsprung-Russel diagram, into an area known as the Giant Branch.
As the outer layers expand, the temperature of the surface will fall,
and its colour will shift towards red.
Mercury will be engulfed by the expanding red Sun,
which will grow to 200 times its size now.
As it swells the Sun will stretch all the way to our Earth’s orbit,
where our own planet’s prospects are dim.
The Sun with the total life time of 10 billion years, will end its days as a red giant star.
This will happen in another 5 billion years.
For a few brief instances the Sun will be 2000 times as bright as it is now,
but that won’t last long.
Eventually our Sun will shed its outer layers, and all that will be left will be its cooling core.
It will become a white dwarf, that will glow pretty much to the end of time,
fading slowly into the interstellar night.
The gas and dust of the dying Sun will drift off into space.
In time they will form a vast dark cloud primed and full of possibilities.
Then over time, another new star will be born.