#CamFest Speaker Spotlight

Dr Helen Mason OBE, a solar scientist at the University of Cambridge who has worked for many years on NASA and ESA solar space observations, reveals some surprising facts about the sun ahead of her two events: The Sun Our Star (25 March) and Sunspaceart: Sun And Solar System Pop-Up (25 & 26 March).

What drew you to solar research?

Since a young age I was fascinated by the stars and astronomy. My first encounter with solar physics was at university. I did some research work on the solar wind for an undergraduate project. I was then offered a place at University College London to do a PhD and the topic was solar eclipse observations. I was hooked and have been studying the Sun ever since.

Can you explain what is meant by the Sun's 'activity cycle'?

The Sun is not constant, it has an 11-year cycle of activity. The most evident manifestation of this is the number of sunspots. These have been observed since the time of Galileo. Sometimes there are no sunspots and sometimes the Sun is covered in sunspots. The sunspots indicate regions where the magnetic field on the Sun is very strong and has broken through the surface. They are dark because they are slightly cooler than the rest of the Sun's surface, and because of the strong magnetic field the energy carried from lower layers is inhibited. Hence, this is really a cycle of magnetic origin, which is rather complex.

Why does it go through this activity phase? And does it affect Earth in any way?

This activity cycle is caused by processes inside the Sun (the dynamo effect) which produces a magnetic field inside the Sun, and brings it to the surface. The Sun is made of gas and does not rotate like a solid body, it has a 'differential' rotation. The magnetic field gets twisted up inside around like a ball of string. When it breaks through the surface, it unravels and 'dissipates'. When the Sun is magnetically active, Solar Maximum, there are lots of dynamic phenomena like solar flares in those sunspot regions, which can impact on the Earth's environment ('space weather'). When the Sun is quiet, with no sunspots, it is very peaceful. Currently, the Sun is getting rather active, and this is manifest by beautiful aurorae. Now is a good time for a trip to the North of Scotland or the Arctic, Iceland or north Norway.

What are the most surprising things researchers have learnt about the Sun in recent years?

The solar corona, outer atmosphere of the Sun, seen during a total eclipse, is very hot, over one million degrees, even though the solar surface (photosphere) is closer to 6,000 degrees. This was totally unexpected. The mechanism for heating the solar corona has long been a mystery, captivating solar researchers. In recent years, we have made progress in understanding how energy is channelled up into the corona by its magnetic field and released. From observational evidence (mainly from space observations) combined with theoretical models, we now believe that small 'nano-flares' could play an important role. These happen when the magnetic field gets twisted and tangled, and then suddenly snaps back into a smoother configuration (called 'magnetic reconnection'). This can happen on small scales ('nano-flare') or in huge explosions (solar flares). The processes are complex, and it is thought that waves may also play a role. Recent solar observatories (for example the Solar Dynamics Observatory) have changed our whole perspective on the Sun.

Has anything ever landed on the Sun?

The Sun is very hot, 15 million degrees in its core, 6,000 degrees on its surface. At these temperatures, everything is a gas (plasma, hot magnetised gas), so it doesn't have a surface on which to land. Even if it did, it would be too hot to land there. However, there are currently two solar spacecraft, NASA's Parker Solar Probe and ESA's Solar Orbiter which are travelling very close to the Sun. The aim is to study the features on the surface of the Sun and the gas (solar wind) which flows from the Sun and impacts the Earth's environment. These spacecraft have advanced technology with special materials (heat shields), to protect them from the heat of the Sun. No human could ever endure such temperatures.

What has been the biggest ever breakthrough / discovery in solar research?

One major breakthrough in solar research was made by an eminent scientist, Eugene Parker. He worked out that the gas (plasma) from the Sun is flowing out into what we call the 'solar wind', which impacts the Earth's environment. No-one really believed him and when he submitted his paper to the Astrophysical Journal, the referees (peers who read the paper and comment on it) rejected it. Fortunately, the editor, Subrahmanyan Chandrasekhar, also an eminent scientist, overruled them and published his paper, saying that he could not see anything wrong in his calculations. It is now the seminal work in this field of research.

Parker also proposed the notion of 'nano-flares', now thought to be fundamental in the process of coronal heating. He was recently honoured, with NASA's Parker Solar Probe being named after him. Fortunately, he lived long enough to watch its launch in 2018. I have had the honour to meet this great scientist and to listen to an amazing talk he gave about stellar astronomy and how important it is to study the Sun.

Is the Earth moving away from the Sun?

The Sun is indeed getting farther away from Earth over time.

On average, the Earth is about 93 million miles (150 million kilometres) from the Sun. However, its orbit is not perfectly circular, it's slightly elliptical, or oval-shaped. This means Earth's distance from the Sun can range from about 91.4 million to 94.5 million miles (147.1 million to 152.1 million km). However, the Earth is very slowly getting further away from the Sun.

Does The Sun have a lifetime? And do we know when it will end?

The Sun was 'born' about 4.5 billion years ago, and it will live for another 6 billion years. However, it will grow into a 'red giant' and the outer atmosphere will explode off leaving a 'white dwarf' in the centre. This astrophysical object is called a 'planetary nebula'. Had the Sun been 10 times more massive it might have had a more spectacular end as a super-nova explosion with a black hole in the centre. We know this because we can see other stars in the night sky at different stage of their lifetime. The Sun is after all just an ordinary star, but very special for us!