What is the solar cycle?

Our Sun is a huge ball of electrically-charged hot gas. This charged gas moves, generating a powerful magnetic field. The Sun's magnetic field goes through a cycle, called the solar cycle.

Every 11 years or so, the Sun's magnetic field completely flips. This means that the Sun's north and south poles switch places. Then it takes about another 11 years for the Sun’s north and south poles to flip back again.

The solar cycle affects activity on the surface of the Sun, such as sunspots which are caused by the Sun's magnetic fields. As the magnetic fields change, so does the amount of activity on the Sun's surface.



This visualization represents the constant changing of the Sun’s magnetic field over the course of four years. Video credit: NASA's Scientific Visualization Studio

One way to track the solar cycle is by counting the number of sunspots. The beginning of a solar cycle is a solar minimum, or when the Sun has the least sunspots. Over time, solar activity—and the number of sunspots—increases.

The middle of the solar cycle is the solar maximum, or when the Sun has the most sunspots. As the cycle ends, it fades back to the solar minimum and then a new cycle begins.

Images of the Sun during one solar cycle. Solar maximum occurred during 2001 while 1996 and 2006 were near solar minimum.

Images of the Sun during one solar cycle. Solar maximum occurred during 2001 while 1996 and 2006 were near solar minimum. Image credit: NASA

Giant eruptions on the Sun, such as solar flares and coronal mass ejections, also increase during the solar cycle. These eruptions send powerful bursts of energy and material into space.

This activity can have effects on Earth. For example, eruptions can cause lights in the sky, called aurora, or impact radio communications. Extreme eruptions can even affect electricity grids on Earth.

An image of a coronal mass ejection observed by NASA’s Solar and Heliospheric Observatory, or SOHO, satellite in 2001. Credit: ESA/NASA/SOHO

An image of a coronal mass ejection observed by NASA’s Solar and Heliospheric Observatory, or SOHO, satellite in 2001. Credit: ESA/NASA/SOHO

Some cycles have maximums with lots of sunspots and activity. Other cycles can have very few sunspots and little activity. Scientists work hard to improve our ability to predict the strength and duration of solar cycles. These predictions can help them forecast these solar conditions, called space weather.

Forecasting of the solar cycle can help scientists protect our radio communications on Earth, and help keep NASA satellites and astronauts safe, too.

NASA Astronaut Tim Kopra on a 2015 spacewalk outside the International Space Station. Credit: NASA

NASA Astronaut Tim Kopra on a 2015 spacewalk outside the International Space Station. Credit: NASA

Solar activity can affect satellite electronics and limit their lifetime. Radiation can be dangerous for astronauts who do work on the outside of the International Space Station. If scientists predict an active time in the solar cycle, satellites can be put into safe mode and astronauts can delay their spacewalks.

article last updated October 31, 2017
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