2023-10-28 17:04:58
Radio broadcasts from the Sun have been studied since the beginning of the second half of the 20th century. Very recently, radio astronomers from Center for Solar-Terrestrial Research (NJIT-CSTR) from the New Jersey Institute of Technology have captured the image of a solar eclipse in a way never seen before and most importantly by recording the first radio images of the famous “ring of fire” effect of the eclipse of October 14, 2023.
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Solar eclipses have been known to humanity for millennia but, until the 20th century, they might only be observed in the visible. This was also the case more generally for the study of our host star but everything will change with the beginnings of radio astronomy and the accidental discovery in 1933 by Karl Jansky radio signals of cosmic origin. In fact, from the end of the 19th century and Hertz’s experiments corroborating James Maxwell’s prediction of the existence of electromagnetic waves, several people had thought that the Sun might emit electromagnetic waves and had looked for them… without success.
Instruments were needed with a sensitivity that these researchers did not have and what’s more, in 1902, when the ionosphere was discovered and it was realized that this layer of ionized gas in the upper atmosphere behaved like a mirror for known radio waves, it was even thought that nothing might be detected in the future because the layer had to reflect all astronomical radio emissions from space, making them undetectable for observers on the ground.
The Sun, a radio source increasingly studied since the 1950s
Fortunately, we were wrong and the work on radars during the Second World War accelerated the development of technologies which will quickly lead to modern radio telescopes and the study of the Sun in the radio domain as was the case, for example, since the 1950s in France with the inauguration of the Nançay radio astronomy station (it is used in particular today to hunt gravitational waves). In fact, it was English radars during the war which discovered the Sun’s emissions and before Nançay, a solar eclipse had even been observed at Marcoussis in centimeter and metric waves with antennas bought from the surplus of the American army in Africa in 1951.
Today, for the first time, an annular eclipse has been observed in the radio domain, that of October 14, 2023, and the instruments used are those of theOwens Valley Radio Observatory – Long Wavelength Array (OVRO-LWA). in the United States, in the state of California, regarding 400 kilometers north of Los Angeles in the Owens Valley.
Radio observations withOwens Valley Radio Observatory – Long Wavelength Array made it possible to produce the short video below which we owe to Sijie Yu therefore showing the annular eclipse at several radio wavelengths. We thus see on these images reconstructed in false colors the visible solar disk and the lunar occultation which are delimited respectively by the solid and dotted circles. The radio image of the Sun sometimes becomes distorted due to the refraction of radio waves by the Earth’s fluctuating ionosphere, an effect analogous to what would be seen when observing the Sun beneath a rippling water surface.
The annular eclipse of October 14 was observed for the first time in the radio domain. © Sijie Yu
A solar eclipse that lasts an hour on the radio
If the annular eclipse of October 14 lasted only 5 minutes at most in the United States, the radio phenomenon lasted almost an hour due to the existence of the solar corona formed of plasma which extends well beyond the surface of the Sun from where photons are emitted in the visible, the photosphere. Remember that the solar corona is the outermost layer of the Sun’s atmosphere which extends over nearly ten million kilometers, that is to say approximately 14 times the radius of the Sun.
« Finally see an eclipse of a “ring of fire” this way was spectacular… We have never seen such quality radio imaging of the Sun before », declared, in a press release from New Jersey Institute of Technology, Dale Gary, distinguished professor of physics at NJIT-CSTR and co-investigator of the OVRO-LWA project. “ We normally can’t see the corona from the ground except during a total eclipse, but we can now see it at any time thanks to OVRO-LWA. This eclipse makes the situation even more dramatic “, he added.
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