The day the Sun had no spots

Let's take a look at a picture made on January 28 by MDI onboard of SOHO in visible light (figure above). We see a spotless Sun. SIDC observers and the Catania spotter reported no sunspots that particular day. The flaring activity was accordingly also low.

The graph above is showing the 10cm flux in January. January 29 is day 0. 10cm solar radio flux is a measure for the noise emitted by the Sun at a wavelength of 10.7 cm (frequency around 2800 MHz) and is measured here on Earth. The 10 cm flux is a full-disc measurement which means that all radiation with a wavelength of 10 cm (radio waves) from the whole visible solar surface is counted (integrated as we say). This flux is a proxy for the solar activity. The curve has a 27 days recurrence. Actually, the curve we see in the graph is not reaching very high tops compared to previous curves. The Sun is having a dip?

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