Scientists Say: Solar Cycle

The sun’s activity increases and decreases over this roughly 11-year period 

This long tendril of solar material erupted out from the sun in August 2012. It flew out into space at more than 1,450 kilometers (900 miles) per second. When the sun throws off bits of itself like this, it’s called a coronal mass ejection.

Goddard Space Flight Center/NASA

Solar cycle (noun, “SOHL-err SY-kuhl”)

The solar cycle is a roughly 11-year cycle in the sun’s activity. At the start of each cycle, the sun’s activity is low. It’s at a so-called “solar minimum.” Over an average four years, the sun’s activity rises to a “solar maximum.” Over another seven years or so, it quiets back down to a solar minimum.

The sun goes through this cycle because of its magnetic field. Sort of like a giant bar magnet, the sun has a huge magnetic field with a North and South Pole. But the sun’s magnetic field is very messy. It’s always stretching and twisting. This happens due to the churning of hot plasma inside the star. As a result, the sun’s magnetic field completely flips every 11 years or so. Its North Pole becomes its South Pole, and vice versa. That drastic change affects the activity on the sun’s surface.

Near the solar maximum, the sun has more sunspots. These are dark splotches on the sun with especially strong magnetism. A solar maximum also tends to come with more eruptions on the sun’s surface called solar flares. And it usually brings more coronal mass ejections, or CMEs. These are huge plumes of hot, magnetized plasma that get blasted away from the sun into space. Both solar flares and coronal mass ejections can affect technology on Earth — interfering with satellite signals, causing power outages and more.

But the solar maximum isn’t all bad news. It’s also an exciting time for sun-related science. The upcoming April 8 total solar eclipse will happen near the sun’s solar maximum. This will make the eclipse a great opportunity to see lots of activity in the sun’s outer atmosphere — and maybe even a dramatic coronal mass ejection.

In a sentence

Neptune’s weather seems to shift along with the solar cycle.

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Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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