Ever since she first looked at the Sun through a solar telescope, Lucie Green has been fascinated with finding out how it works. Although our closest star has given up many of its secrets over the years, there is still a great deal left to discover about the huge ball of plasma that provides our heat and light. Working at University College London’s Mullard Space Science Laboratory, and alongside space agencies such as NASA and the European Space Agency, Green is involved in some exciting projects to learn more about our host star. From studying giant eruptions on its surface to measuring strong solar winds, she hopes to be able to answer some of the biggest questions about not just the Sun, but the entire universe too. We caught up with her to discuss how she plans to get closer to the heart of our Solar System than ever before.
When did you first become interested in studying the activity of our nearest star?
The turning point for me was during a visit to the Crimean Astrophysical Observatory. I’d gone there as an undergraduate on a work experience trip organised by one of my tutors, and we were due to use their large telescopes to do studies of high-mass x-ray binaries, two-star systems that give off a lot of x-rays. We also had a tour of the site and one of the ladies showed us the solar telescope that she operated. It was that view of the sun through her telescope that made me realise that I didn’t know that much about the sun at all. Seeing it in the light of hydrogen alpha, which shows you a particular part of its atmosphere, made me realise that it was a much more dynamic and interesting star that I had previously thought.
Why is it important to study the Sun?
The Sun is the star that we can study in the most detail because it’s the closest star to us. When we look at the Sun, we see the whole object. We can see the surface, the atmosphere, and we can make out certain features, whereas when you look at the majority of other stars, they’re just points of light. So the Sun ends up being a bit like a Rosetta Stone for other stars. We can develop techniques to understand what’s happening on the Sun and then apply them across the universe. Another reason is that solar activity has an impact on our planet. It drives space weather, which can have a negative impact on our technology.
“The Sun’s activity follows an 11-year cycle, and we know that this is driven by an evolution of its magnetic field”
How much do we already know about how the Sun works?
We’ve been observing the Sun with telescopes for over 400 years, and from space since the 1940s, so we have a good observational description of what the Sun does. We are now trying to see the physical processes happening at smaller and smaller size scales that we can’t make out with our telescopes.
Another thing we want to know is how the solar cycle works. The Sun’s activity follows an 11-year cycle where it rises and falls and we know that this is driven by an evolution of the Sun’s magnetic field. However, because it occurs inside the Sun where it is very hard to probe, we don’t have a fully developed physical understanding of how it operates as a star.
What technology is being used to try and answer these questions?
On the ground we have detectors that look at the Sun in the wavelengths of light that make it through the atmosphere, such as visible light and some parts of the radio spectrum. Then we can also do detections of particles on the Earth as well. For example, a by-product of the fusion process that powers the Sun is particles called neutrinos, and you can measure those neutrinos on the ground.
There’s also a lot that we want to do from space, in particular focusing on parts of the Sun’s emissions that we can’t detect on the Earth. For example, wavelengths of light like ultraviolet, X-rays and gamma rays that don’t make it through the Earth’s atmosphere.
Another benefit of being above the atmosphere is that we get a much clearer view. For example, we have telescopes that create artificial solar eclipses, called coronagraphs, and they are typically flown in space. Using these coronagraphs you can see the ejections that the Sun sends out into the Solar System, so you get a crisper view of one of the forms of solar activity.
What projects are you currently working on?
One project I’m working on is Solar Orbiter. It’s a really ambitious project, a sort of Icarus-like mission to fly close to the Sun and take close-up pictures. However, as well as taking images, the spacecraft will sit in the flow of material that constantly comes out of the Sun, so we can sense it directly as it washes over it.
That’s going to allow us to answer some of the big questions about the Sun. For example, the Sun produces a strong wind but we don’t know exactly how it is produced. Solar Orbiter is going to measure the wind as it blows over the spacecraft, so we will be able to work out what it’s made of, the temperature of it, what magnetic field is in it, the characteristics of it and then try and understand more information about how that wind is formed.
“Telescopes in space can create artificial solar eclipses, so you get a crisper view of solar activity”
How will you overcome the challenges of getting a spacecraft near to the Sun?
The side facing the Sun will heat up to 600 degrees Celsius, and as you can imagine, you can’t have that heat falling on your instruments. A heat shield has been developed that stops that intense radiation falling on the main part of the spacecraft. Also, because the orbit of this spacecraft goes close to the Sun then takes it further out again, its temperature is changing from hot to cold and back again, so we need to create a stable environment behind that heat shield. Solar Orbiter has solar panels that will tilt so that you can regulate how much light is falling on them as you get closer to or further away from the Sun.
What other big space stories have you been most excited about recently?
Mars is the focus for me at the moment. I am working on a European Space Agency mission to go to Mars so I’m always keeping an eye on what the rovers are looking at. Then there’s Pluto and the New Horizons mission. The images taken by that spacecraft are absolutely incredible. I can’t believe there are floating mountains on Pluto, and vast nitrogen plains. They are still downloading data from the spacecraft, so I can’t wait to see more results.
What is your favourite fact about the Sun?
I think it has to be that the sunlight that we see takes about eight minutes to get from the sun to us. But it has been created near the centre of the sun and taken nearly 170,000 years to get from the centre to the surface. That’s because the material inside the sun is very different to the material between the sun and us.
Lucie Green’s astronomy top tips
Learn the constellations
“Start off by familiarising yourself with the night sky. Orion is my favourite constellation because it’s got everything, including star-forming regions and stars that have been kicked out of the constellation in the past.”
Get kitted out
“Buy a pair of binoculars and then work up to having a telescope. You can also get lots of support and share in the excitement of learning about astronomy by joining a local astronomical society.”
Look at the moon
“You can look at the Moon during the different phases, and spot different craters. You can really get a feel of the 3D nature of the surface by looking at the shadows that are cast. I never tire of getting my binoculars out and looking at the Moon.”
Lucie Green’s new book 15 Million Degrees: A Journey To The Centre Of The Sun is out now.
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