Sunspot Cycle
Written by Fraser Cain
Galileo Galilei made a huge number of revolutionary discoveries when he pointed his first rudimentary telescope at the skies in 1610. One of these was the discovery that the Sun isn't a pristine ball, but actually had blemishes that moved across its surface. Galileo was the first to discover sunspots.
From this point on, astronomers were hard at work cataloging the size and number of sunspots, and they learned that the rise and fall in the number of sunspots follows an 11-year period – this is the sunspot cycle.
Astronomers now maintain the "sunspot number". They add up the total number of sunspot groups, and the count the number of individual sunspots. And these observations have been made for over 300 years. Sometimes the sunspot cycle can be as short as 9 years and other times as long as 14 years. But on average, it takes 11 years.
At the height of solar activity, there can be dozens of sunspots on the surface of the Sun at the same time, and at the lowest points, the Sun can go days without sunspots. When the Sun is most active, it releases more flares and coronal mass ejections, so astronomers are continuing to gather data about the sunspot cycle, to better predict solar weather. This will be especially important when the first astronauts travel to the Moon, and could be at risk to a radioactive solar storm.
Why does the sunspot cycle rise and fall like this? Scientists just aren't sure. It's all connected to the Sun's magnetic field, which twists and turns as it rotates. Sunspots occur at the points where the magnetic field lines pierce the surface of the Sun.
But why it takes 11-years between minimum and maximum? Nobody knows. One theory is that it has something to do with the tidal interactions between the Sun, Jupiter and Saturn.
Here's an article from Universe Today about a puzzling lack of sunspots, and
another article about how the Sun burst into light during a cycle.
Here's a page from NASA that explains the sunspot cycle, and a bunch of charts from NOAA.
We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.
Filed under: Astronomy
