Left: April 2014; right: December 2019  

You can't be blamed for not noticing the shift. There were no flashes of light, no cosmic trumpets. Just an appearance of low-temperature shadows called sunspots at high latitudes.

"We keep a detailed record of the few tiny sunspots that mark the onset and rise of the new cycle," says Frédéric Clette, director of the World Data Center Sunspot Index and Long-term Solar Observations.

"These are the diminutive heralds of future giant solar fireworks. It is only by tracking the general trend over many months that we can determine the tipping point between two cycles."

In practice, variations in the Sun's behaviour make it impossible to identify a fresh start until it's passed. It took sifting through data on solar activity from the past eight months to confirm last year was as boring as the Sun is going to get for the next decade.

In spite of centuries of careful recording of these 11 year cycles, we still don't have the mechanisms behind these cycles fully worked out. Periodicity in stars is pretty common; looking out into the Universe, there are a variety of pulsating objects that seem to flare and darken at intervals you could almost set your watch by.