Our Sun might seem like an unchanging feature of our sky, but it’s actually a lot more changeable than you might think. Now, it’s heading towards its period of lowest activity. This is called the solar minimum, when the Sun’s activity reaches its lowest point. We see fewer flares coming our way and fewer sunspots too. But why the solar minimum occurs is still a bit of a mystery.
The solar cycle takes about 11 years, as the Sun moves from its solar maximum to solar minimum and back again. The last solar maximum came in 2014, with a solar minimum expected in 2019 or 2020. During this period, there will be a lot fewer visible sunspots on the Sun and fewer solar flares.
What does it mean for us? Well, it’s probably not going to change things much on the ground. But up in space, it can cause quite dramatic changes. NASA has described what happens in a handy video, below.
One of the effects it will cause is in low-Earth orbit, where satellites and space junk often have to contend with atmospheric drag enhanced by solar flares hitting the atmosphere. During a solar minimum, there is less atmospheric drag – which is good for satellites, but bad for cleaning up space junk.
The name itself is a bit of a misnomer, because while the activity is lessened, the Sun is still up to tricks. Specifically, it can develop coronal holes, vast gaps in its magnetic field that allow fast-moving particles from inside the Sun to escape. When they hit our magnetosphere, they can cause space weather effects like geomagnetic storms and aurorae.
“We see these holes throughout the solar cycle, but during solar minimum, they can last for a long time – six months or more,” said Dean Pesnell of NASA's Goddard Space Flight Center in the video.
Plus, the solar minimum can also be a danger for astronauts, as our atmosphere lets in more galactic rays. These high-energy particles from elsewhere in the universe, like supernovae, can pose health risks.
As mentioned earlier, we still don’t really know exactly what drives the solar cycle. We’re pretty sure it’s related to the Sun’s magnetic field, but the exact workings of it isn’t clear. We do know a bit more about the effects of it though, so expect to see plenty more news about the solar minimum over the next few years as the Sun quietens down.