What is solar physics and space weather?
The Sun‘s atmosphere is a hotbed of activity. Huge amounts of energy stored in twisted and stressed magnetic fields are released over time scales of minutes, resulting in emission of light from gamma-rays to radio waves, particle acceleration to near light-speed, and the eruption of billions of tons of charged gas. The release of such huge amounts of energy in the solar atmosphere provides astronomers with an opportunity of studying matter in extreme environments, giving an insight into the fundamental physics of charged gases (known as plasmas) and the high energy particles with which they are often associated. The study of the plasmas and particles of the sun, from the very smallest scales to the very largest, is collectively known as solar physics.
While such powerful releases of energy provide an interesting means to study the fundamental nature of our nearest star, such events can also impact our lives on Earth on a regular basis. During the energy release, the huge quantities of charged gas and high-energy particles may be directed at Earth. Such eruptive activity is known collectively as a ‘solar storm’. Once this storm arrives in the near-Earth environment it may the familiar glow of the Aurora Borealis, but it can also pose a risk to telecommunications satellites, electrical power grid systems, astronauts during space walk, and even passengers on flights close to the Earth’s poles. Because of these risks, there is an effort to try and understand both the causes of solar storms and their potential threat to life and technology on Earth. The study of the origin of solar storms, and how to ultimately predict any threat they may pose, is known as space weather.
What is solar radio physics?
Even during inactive periods the solar atmosphere can reach temperatures as high as 1 million degrees Celsius. During active times, the sun can heat parts of its atmosphere to tens of millions of degrees and accelerate particles to near light-speed. Such atmospheric conditions result in the sun emitting light from across the entire electromagnetic spectrum, from gamma rays (the highest energy light) to radio (the lowest energy). Each type of light allows scientists to probe a specific part of the solar atmosphere and also identify specific physical processes. The very longest wavelength radio light from the sun is particularly good at giving us insight into how high energy particles behave. When the particles are accelerated they may emit various kinds of radio emission. Analyzing the specific types of radio emission can tell us how hot the solar atmosphere is, how dense it is, how strong the solar magnetic field is and how much energy the particles themselves have. Such knowledge is extremely important for developing our understanding of the solar atmosphere on a fundamental basis and also exploring the origins of particles that can pose a space weather threat.
How do we observe radio emission from the sun?
Much like visible light, we observe the radio universe using telescopes. While visible-light telescopes usually use glass lenses and mirrors, radio telescopes use antennas and dishes, much the same as those used for TV or mobile phone communications. The concept may be the same as visible light telescopes, but radio telescopes are often much larger and require sophisticated techniques in order to produce radio images. The primary technique is to construct a connected network of radio antennas over a large area, sometimes covering
hundreds of kilometers. Signals from from each antenna in the network are combined allowing the antennas to act in unison and be used as a single enormous telescope. This is the method of observation of multiple solar dedicated instruments including the Nançay Radioheliograph in France (NRH), the Nobeyama Radioheliograph in Japan (NoRH) or the Chinese Spectral Radioheliograph. The current state of the art in such technology are known as ‘phased-array interferometers’ such as the European-wide Low Frequency Array (LOFAR) and the Square Kilometer Array (SKA, https://www.skatelescope.org/) now being built in South Africa and Australia. These instrument require a worldwide concerted effort in astrophysics, communications technology and the burgeoning new fields of ‘big data’. Although still under development, instruments such as the SKA and LOFAR represent the forefront of astrophysics, and are already providing unprecedented observations of the radio universe. Such observations are essential for the development of our understanding of the physical processes that govern the sun and how it affects life on Earth.