Solar minimum is the regular time of lowest activity in the Sun's 11-year cycle. During solar minimum, sunspots and solar flares become less frequent, and sometimes do not happen for several days. The solar cycle usually lasts about 11 years, but the time between solar minima can range from 9 to 14 years. The exact date of a solar minimum is determined by averaging sunspot activity over 12 months, which means the date is typically identified about 6 months after the minimum occurs. Solar minimum is the opposite of solar maximum, when hundreds of sunspots can appear.

Solar minimum and solar maximum

Solar minima and maxima are the two extremes of the Sun's activity cycle, which lasts about 11 years and 400 years. During a maximum, the Sun has many sunspots, solar flares happen, and the Sun sends large clouds of charged gas into space. People who watch the sky may see more auroras, and space agencies need to watch for radiation storms to protect astronauts. Power outages, satellite problems, communication issues, and GPS errors are some of the possible effects during a solar maximum.

During a solar minimum, there are fewer sunspots, and solar flares become less active. Sometimes, days or weeks pass without any sunspots appearing.

Predicting solar minimum cycles

The sun's activity does not follow a simple pattern, making it hard to predict changes in solar activity. A solar minimum is a time when the sun is less active, with very few or no sunspots. Scientists from the National Center for Atmospheric Research (NCAR) created a computer model called the Solar Dynamo to better predict solar activity. This model was tested and showed more than 98% accuracy in predicting the strength of the past eight solar cycles. However, the predictions were later found to be very wrong and did not match the actual sunspot numbers observed.

Between 2008 and 2009, NASA scientists noted that the sun was entering a "deep solar minimum." They reported that there were no sunspots on 266 of 2008's 366 days, which is 73% of the year. Some scientists believed the solar cycle had reached its lowest point in 2008. Sunspot numbers in 2009 dropped even further. By September 14, 2009, there were no sunspots on 206 of the year's 257 days, which is 80%. Solar physicist Dean Pesnell of the Goddard Space Flight Center stated, "We're experiencing a very deep solar minimum." Other experts agreed. David Hathaway, a sunspot expert from NASA/Marshall Space Flight Center, said, "This is the quietest sun we've seen in almost a century." However, the sun's activity remained higher than during a grand solar minimum.

Grand solar minima and maxima

Grand solar minima happen when several solar cycles have less activity than usual for many years or even centuries. During these times, solar cycles still occur, but they are weaker than normal. Grand solar minima are a special way that the solar dynamo works.

A list of historical grand solar minima includes events that occurred around 690 AD, 360 BC, 770 BC, 1390 BC, 2860 BC, 3340 BC, 3500 BC, 3630 BC, 3940 BC, 4230 BC, 4330 BC, 5260 BC, 5460 BC, 5620 BC, 5710 BC, 5990 BC, 6220 BC, 6400 BC, 7040 BC, 7310 BC, 7520 BC, 8220 BC, and 9170 BC.