BENGALURU: It is possible to measure the Sun’s magnetic field using commercial dish TV antennas. In a major breakthrough to study the Sun, the radio astronomy group at the Indian Institute of Astrophysics (IIA), Bengaluru has proved that low-cost dish antennas that are used for TV networks can be used to observe the Sun and its magnetic field.
“The scientific and technical personnel at IIA, associated with the Gauribidanur radio astronomy field station near Bengaluru, are successfully operating a unique and large world-class radio antenna array for regular observations of the solar corona and magnetic field.
The observations are carried out every day unlike the optical observations, where the solar corona can be observed from the ground only during a total solar eclipse. The radio observations are not affected by the clouds,” said Prof R Ramesh, senior professor at IIA.
He is in charge of the institute’s radio astronomy field station at Gauribidanur and is the principal investigator for the VELC instrument on board Aditya-L1, India’s maiden space mission for dedicated observations of the Sun.
“The solar corona overlying the Sun’s photosphere as well as present beyond its limb can be observed with a radio telescope. These are unique advantages of radio observations. The antennas used in the array are designed and fabricated in the Gauribidanur observatory workshop. The analog and digital receiver systems are also developed in-house using off-the-shelf components,” he added.
While the measurement of the Sun’s magnetic field at its visible surface (the photosphere) is routinely carried out with both ground and space-based observational facilities, regular measurements of the extension of the same magnetic field to the outer layers in the Sun’s atmosphere like the chromosphere and corona are not there.
“It is important to establish the connection between the magnetic field on the surface of the Sun and its outer atmosphere to understand and possibly predict eruptive mass ejections from the corona, called the Coronal Mass Ejections (CMEs),” said Ramesh.
CMEs are the most powerful explosions happening in our solar system, and are caused primarily by magnetic field instabilities. “It is necessary to estimate the Sun’s magnetic field on its surface, chromosphere and corona. When a CME blows past the Earth, it can damage the electronics in the satellites in near-Earth space, and disrupt radio communication networks on Earth. These are called space weather disturbances,” he added.
Over the last couple of years, the IIA Gauribidanur team has been working to establish a similar facility for measuring the magnetic field in the solar chromosphere also, to bridge the gap between the measurements in the photosphere and corona.
Their efforts show that it is possible to measure the magnetic field in the solar chromosphere (the region between the Sun’s photosphere and corona) using simple and cost-effective commercial dish TV antennas that are in most households. “The antennas operate at a frequency of 11.2 GHz, which is in the radio astronomy band of the electromagnetic spectrum. This novel and unique effort paved the way for regular measurement of the Sun’s magnetic field from its surface to the outer layers of its atmosphere with ground-based observational facilities.
The IIA team has used radio telescopes in Gauribidanur to simultaneously measure the Sun’s magnetic field in both the chromosphere and corona. The antenna and receiver system are modular, and can be augmented to achieve more sensitivity and higher angular resolution,” he said.