Seven Years of Tracking the Solar Cycle
Our sun is ever-changing, and a satellite called the Solar Dynamics Observatory has a front-row seat.
On February 11, 2010, we launched the Solar Dynamics Observatory, also known as SDO. SDO keeps a constant eye on the sun, helping us track everything from sunspots to solar flares to other types of space weather that can have an impact on Earth.
After seven years in space, SDO has had a chance to do what few other satellites have been able to do – watch the sun for the majority of a solar cycle in 11 types of light.
The sun’s activity rises and falls in a pattern that lasts about 11 years on average. This is called the solar cycle.
Solar activity can influence Earth. For instance, it’s behind one of Earth’s most dazzling natural events – the aurora.
One of the most common triggers of the aurora is a type of space weather called a coronal mass ejection, which is a billion-ton cloud of magnetic solar material expelled into space at around a million miles an hour.
When these clouds collide with Earth’s magnetic field, they can rattle it, sending particles down into the atmosphere and triggering the auroras. These events can also cause satellite damage and power grid strain in extreme cases.
The sun is in a declining activity phase, so coronal mass ejections will be less common over the next few years, as will another one of the main indicators of solar activity – sunspots.
Sunspots are created by twisted knots of magnetic field. Solar material in these tangled regions is slightly cooler than the surrounding areas, making them appear dark in visible light.
The tangled magnetic field that creates sunspots also causes most solar activity, so more sunspots means more solar activity, and vice versa. Humans have been able to track the solar cycle by counting sunspots since the 17th century.
Image: Houghton Library, Harvard University, *IC6.G1333.613ia
The peak of the sun’s activity for this cycle, called solar maximum, was in 2014.
Now, we’re heading towards the lowest solar activity for this solar cycle, also known as solar minimum. As solar activity declines, the number of sunspots decreases. We sometimes go several days without a single visible sunspot.
But there’s much more to the story than sunspots – SDO also watches the sun in a type of light called extreme ultraviolet. This type of light is invisible to human eyes and is blocked by our atmosphere, so we can only see the sun this way with satellites.
Extreme ultraviolet light reveals different layers of the sun’s atmosphere, helping scientists connect the dots between the sunspots that appear in visible light and the space weather that impacts us here on Earth.
SDO keeps an eye on the sun 24/7, and you can see near real-time images of the sun in 11 types of light at sdo.gsfc.nasa.gov/data.
