Tip:
Highlight text to annotate it
X
Our existence depends on the Sun. When clouds get in the way or we rotate away
from it on the Earth and have our night time - it's there, radiating light in all directions
and sustaining life on Earth.
However you don't get something for nothing. The Sun is shining bright,
but how long will it last? How long has it been there for?
In astronomy most research is done with telescopes, but this isn't always the case.
Over 40 tonnes of material falls on the Earth every day and sometimes the pieces are large
enough to survive their fiery journey through the atmosphere and reach the ground.
These space rocks, called meteorites, contain the information we need to find out the age
of our solar system.
If we wanted to find out the age of an ancient Egyptian mummy we could use a technique called
carbon-dating. However, meteorites don't contain life as
far as we know but we could use another method to determine their age -- rubidium dating.
We can study the decay of the element rubidium and find out their age but how does this help
us find the age of the Sun? Well the Earth, the planets, comets and moons all formed at
the same time as the Sun, so space rock rubidium tells us the Sun is 4 and a half billion years old.
But what does this number mean? Is our Sun
young? Is it middle-aged or is it collecting its pension?
To answer this we need to delve deeper into the Sun itself.
At the heart of our star the temperature hits an unimaginably hot 15 million degrees Celsius.
Here bits of hydrogen are fused together producing helium and energy.
In these reactions a small amount of the mass is converted into energy.
The conversion is outlined in Einstein's famous equation: E = mc2. Here E is the energy released,
m is the missing mass that has changed into energy and c is the speed of light.
The Sun does not have a limitless supply of fuel, it will eventually run out of hydrogen
but when? Well to work this out first of all we need
to weigh the Sun. Set aside those cosmic weighing scales, we
need to bring in two astronomical heavyweights -- Johannes Kepler and Isaac Newton.
Kepler studied the motions of the planets and didn't quite understand why they stayed
in orbit around the Sun until Newton came along 80 years later and formulated gravity.
Using Kepler's laws and Newton's laws of gravitation the mass of the Sun can be calculated as being
equivalent to four thousand trillion trillion hippos.
So fast forward 200 years and we have E = mc2 and the mass of the Sun. Now we have the tools
to work out how much energy is thrown out from the Sun.
We have yet to obtain detailed blueprints for the inside of a star but star models assume
that 10% of the Sun is hot enough to undergo nuclear fusion.
In each reaction 7/10ths of the original hydrogen mass is converted into energy.
That energy eventually spreads out from our star into space like a balloon getting thinner
and thinner. We don't feel the full brunt of this radiation
as we are 150 million km away. We can measure the amount of energy that falls on the Earth
and if we know the distance to the Sun we can work out how much energy leaves the Sun
in the first place.
Finally if we know how much fuel our star has, we can find out how long it will last.
It turns out the Sun is a middle-aged star as it has enough fuel to keep going for another
5 billion years after which the star we know and love will start to look very different.
Hopefully by then we will have colonised another planet and future humans from Earth 2.0 can
witness the next stage in the lifecycle of our Sun.