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My work and career: Smart people in science


My work and career: The importance of the Sun
Joan Feynman Scientist
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[Q] This was your main contribution to so-called space weather. But I want to go to take you back to history of aurora and the visit of corona in Sweden. When you reported why there was no aurora at that time, it was because the solar activity was at the minimum of Centennial Cycle.

Yes. No, everybody knows about the 11 years cycle of the sunspots. They go... they're a few or no sunspots for a year or two and then they gradually go up to a maximum, then down again. And it takes 11 years for them to go through one cycle. That's the sunspots. But they... if you take two sunspots, say, if you took the one at the center of a cycle, in 1900 it was very small. The next one was a little bigger, but it went down to zero and then it wakes and so on. It turns out there's an 88-year cycle in the sunspot and solar wind business which is solar... something in the sun, and I don't think that to this day we know what it is. But I quit two years ago.

That's used to predict the interplanetary condition in planning a spacecraft, you know when it's going to fly, and you could calculate what... from the knowledge now what the interplanetary medium is going to be like. So you can design your... your spacecraft systems so that they can stand that... the way it's going to be without getting knocked out or failing and so on. So that's very important for the solar weather people that they can plan ahead 10 years, 15 years and design their spacecraft and all of its parts to last okay for that time. In the early days they had to overdesign everything. They just made it too heavy too safe and not get as much information as they would now.

We had been observing the solar wind particles and fields for a long enough time to be able to make reasonable predictions. It involves an enormous amount of data and analysis of it. And it's a basis of... I believe it's still the basis of predictions for spacecraft design.

The sun has a hot corona, I believe and there are particles that come from it. The particles that come from it depend on the organization of the magnetic field on the surface of the sun. So that in some places it's weaker, which allows more particles to come out and some places stronger, so there are fewer particles and the sun's rotating all the time. So what you get at earth would be variable because of that. But more important perhaps is that the sun has flares, solar flares which are events, which at the sun... there's a sudden reorganization of the magnetic field. So that if it was in two arches before, it's now in one larger arch and the solar wind is much stronger and... so that the danger of being upset by the solar wind becomes more important. And that also has to be dealt with by a process of having observed long enough to understand what's going to happen in the next ten years. And that's a thing which I worked on with many... several other people. And I'm sure that since I left it's still being worked on. It has to be kept up to date because the sun doesn't repeat itself every 11 years.

[Q] Why is this important?

This is important because when you design an experiment, you have to know that the implement that you're putting up there is one that can measure that. Which means that if it's high fluxes you are interested in, you have to design a spacecraft which has instruments which safely observe higher fluxes than you expect to get. Otherwise, you'll never find the maximum. So depending on what it is you're interested in and why, the spacecraft has to be designed so it will last and work throughout the entire project.

Now, there are many projects now that are trying to get closer to the sun where the particles are... much more of them and are hotter and more dangerous, but they can't be measured in the other way. And so this is a thing which has been hanging around about the sun for a long time. And I think they have plans to do it again, is that right? Yes, they want to get closer because there's a region in there that we've never been able to send instruments into. That we have to guess from what we have been able to send the instruments and figure out how it goes from one place... how it influences the different areas outside the sun or in the solar atmosphere.

There are so many people working in this that it's very hard to say exactly what the situation is. For instance, I wrote a paper in 1973 about the helium abundance in the sun. And I discovered that there were about seven or eight different ways they determined this, but they tested each way against the other ways. So they argued that this one was 2% and that one was 2%. But there was no particular reason why they should be the same. And we, in fact, had no idea. And I published that paper which made quite a stir, but I don't know if we yet have any idea of the distribution in the sun of helium. Helium isn't made like other... Well, never mind, it gets often into an entirely different subject of the origin of different chemicals like carbon and things like that which are made in solar explosions.

Joan Feynman (1927-2020) was an American astrophysicist. She made important contributions to the study of solar wind particles and fields, sun-Earth relations and magnetospheric physics. In particular, Feynman was known for developing an understanding of the origin of auroras. During her career, Feynman was an author or co-author of more than 100 scientific publications. She also edited three scientific books. In 2002, she was awarded NASA's distinguished Exceptional Achievement Medal.

Listeners: Alexander Ruzmaikin Christopher Sykes

Christopher Sykes is an independent documentary producer who has made a number of films about science and scientists for BBC TV, Channel Four, and PBS.

Tags: aurora, science, sun, solar wind, magnetic field, earth's field, helium, solar explosion

Duration: 10 minutes, 43 seconds

Date story recorded: April 2019

Date story went live: 05 November 2019