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2nd of June 2023
Radio waves from a solar flare
A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. In just a few minutes, solar flares heat material to many millions of degrees and produce a burst of radiation across the electromagnetic spectrum, from radio waves to X-rays and gamma rays. Scientists classify solar flares according to their brightness at X-ray energies. There are several categories: C-class flares are small with few noticeable consequences here on Earth; M-class flares are medium-sized, and generally cause brief radio blackouts that affect Earth's polar regions; X-class flares are major events that can trigger radio blackouts around the whole world and long-lasting radiation storms in the upper atmosphere.

On May 4th, an M-class solar flare was detected, with the upper figure above showing the X-ray flux (on a logarithmic scale) over the course of the day, as measured with a Geostationary Operational Environmental Satellite (GOES), operated by the US National Oceanic and Atmospheric Administration. The flare commenced just after 08 UT, peaking a little before 09 UT. Radio waves associated with the flare were detected with the Radio Frequency Interference (RFI) monitoring equipment at Inyarrimanha Ilgari Bundara, CSIRO's Murchison Radio-astronomy Observatory in Western Australia. The lower figure shows the frequency in MHz on the x-axis, and time (in UT hours on May 4th) on the y-axis. The solar flare is seen as the horizontal band at all frequencies above ~70 MHz between 09 UT and 10 UT. (The vertical lines around 250 MHz and 370 MHz are persistent radio emissions from other known sources.) The sun has an 11-year solar cycle, and as we approach the next solar maximum, expected around mid-2025, we can expect an increasing number of solar flares. (Image credits: NOAA, Balt Indermuehle)

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