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This content is taken from the Royal Observatory Greenwich's online course, Our Solar System and Beyond: Teaching Primary Science. Join the course to learn more.
2.12

Royal Observatory Greenwich

Skip to 0 minutes and 7 seconds How do we know how old the Sun is? Our existence depends on the Sun. When clouds get in the way, or we rotate away from it on the Earth and have our nighttime, 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.

Skip to 0 minutes and 51 seconds These space rocks, called meteorites, 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, meteoroids 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 1/2 billion years old. But what does this number mean?

Skip to 1 minute and 35 seconds 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 50 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 equals mc squared. Here, e is the energy released, m is the missing mass that is 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?

Skip to 2 minutes and 21 seconds 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 4,000 trillion trillion hippos. So, fast forward 200 years, and we have equals mc squared and the mass of the Sun. Now we have the tools to work out how much energy is thrown out from the Sun.

Skip to 3 minutes and 6 seconds 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, 7/10 of the original hydrogen mass is converted into energy. That energy eventually spreads out from a 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 kilometres 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.

Skip to 3 minutes and 45 seconds 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 five 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 life cycle of our Sun.

Scientists investigate

In Week 3 we will talk about the importance of keeping your lessons up to date by including the latest scientific findings. In this video (aimed at older pupils aged 11+) you will learn about some important scientific techniques that allow astrophysicists to perform forensics on stars such as the Sun.

Astronomy isn’t just about beautiful images, it is a collaborative process between scientists across all fields and space engineers. Their joint expertise is crucial for investigating the physical and chemical properties of our solar system, stars, galaxies and exoplanets.

We interviewed Dr Emily Drabek-Maunder, Senior Manager Public Astronomy at the Royal Observatory Greenwich, and asked her about her research into star formation and looking for signs of life on moons in our Solar System:

Do you work by yourself or do you collaborate with teams internationally?

With my research, I work with an astrophysicist at Cardiff and we are part of an international group of 30 scientists called PEBBLES (Planet Earth Building Blocks Legacy E-Merlin Survey). In PEBBLES we are trying to understand how planets form. I also work with scientists from the Gould Belt Survey where we are looking for star forming regions. We use telescopes around the world to carry out these surveys.

What type of telescopes do you use?

I use the James Clerk Maxwell Telescope on an extinct volcano called Mauna Kea in Hawaii - this telescope detects infrared and microwave radiation. I also use the APEX and ALMA radio telescopes which are situated in the Atacama desert in Chile. I’ve also used the 30 metre IRAM radio dish located in Granada in Spain. The E-Merlin Survey uses 7 radio telescopes across the UK. Radio waves can travel through the clouds in the UK sky!

Do you travel a lot?

Now that I work mainly in science communication and engaging the public with astronomy, I don’t travel as much as I used to! When most of my time was spent doing research, I would go out to telescopes to collect observational data around twice a year and I would attend conferences abroad where I present my research and network with the rest of the scientific community involved in planetary and stellar science.

In your opinion, what is the most exciting recent discovery?

There are two icy moons around Jupiter and Saturn called Europa and Enceladus - these are very exciting because they have plumes of material erupting from their thick icy shells and scientists are very sure that they both have a global ocean of liquid water beneath the ice. The Cassini spacecraft, which orbited Saturn from 2004 to 2017, passed through the plumes of Enceladus and detected gases such as carbon, hydrogen and methane - a potential food source for microbes (if they exist!).

Is there some other area of astrophysics that you would love to study in the future?

I would love to do something more hands-on and help build some of these telescopes, particularly instruments that go out into space. I’ve been in a clean-room where they remove almost all microbes from telescopes and spacecrafts due to go into space.

Do you think we’ll find life elsewhere?

I think its possible we’ll find life. Life needs liquid water to evolve and recent discoveries show there might be water on Enceladus and Europa and small amounts of water have been discovered on Mars. I think there’s a real possibility there might be life elsewhere.