An ultraviolaet image of arcs of gas flowing around sunspots. (GSFC)
Scientists observing activity on the sun’s surface have noticed that the star is quieter than usual.
As part of its natural processes, the sun goes through cycles of activity that last about 11 years. In the middle of each cycle, solar activity reaches a maximum, which is the point where our sun is now. But this maximum, unlike the last one, has been pretty minimal — it’s the quietest maximum seen in about 100 years.
The sun regularly produces solar flares — bursts of light that come from electromagnetic radiation — and coronal mass ejections (CMEs), which send billions of tons of solar material careening through the solar system at more than a million miles per hour. From a distance, the best way to gauge solar activity is by watching sunspots, which can be seen from Earth with a telescope. (The biggest sunspots would be visible to the naked eye if the sun weren’t damaging to the eye.)
The number of sunspots this cycle peaked at just under 100 during one month, according to C. Alex Young, the associate director for science in the heliophysics division at NASA Goddard Space Flight Center. The last solar cycle peaked at 170 sunspots.
Scientists identify the current cycle, which began in 2008, as cycle 24. The last time the sun was this quiet was cycle 14, which lasted from about 1900 to 1911. The first documented cycle began in about 1755; the sun is roughly 4.5 billion years old.
“Even though we’ve been studying up to 24 cycles, in the big scheme of things we haven’t really been looking at the sun for that long,” Young told weather.com. “So we don’t really know what is normal. It’s really hard to say that a small cycle or a big cycle is normal because we haven’t been looking at them for very long.”
Extreme ultraviolet images of the sun during cycle 23 show activity changing from quiet (1996) to active (2001) and back to quiet (2006). (Steele Hill/NASA/GSFC)
The current quiet maximum, then, is giving scientists a chance to study something that they don’t see very often, adding to our knowledge of the sun. And as far as we can tell, it’s mostly better for Earth, and for humans, when the sun stays quiet.
Solar flares temporarily heat up Earth’s atmosphere, which can cause disturbances in communications systems. CMEs can cause geomagnetic storms, which can disrupt the power grid, among other side effects. And the sun also produces particle storms, harmless to humans safe under Earth’s atmosphere and magnetic field, but potentially damaging to spacecraft and astronauts.
Scientists have not made any link between solar activity and weather on Earth, according to Young.
“People have done a lot of studies of that sort of thing, and so far we don’t have any indication that it has effects on weather,” Young said. “We’re not even sure it has any kind of effect on things like long-term climate.”
Scientists still aren't sure why the sun operates on an 11-year cycle, but they have observed similar cycles in other stars, Young said. The lengths of the cycles seem to be dependent on the star's age, size and other traits.
First up, the basics. Here's the sun's mass, in pounds: 4,385,214,857,119,400,000,000,000,000,000. That's about 333,000 Earths. An empty sphere the size of the sun could hold about a million Earths. At its surface, the sun is about 10,000 degrees Fahrenheit, which is basically frigid compared to the 27 million degrees at its core. (NASA/SDO/AIA)