Solar Maximum 

Every 11 years the sun undergoes a period of activity called the "solar maximum", followed by a period of quiet called the "solar minimum". During the solar maximum there are many sunspots, solar flares, and coronal mass ejections, all of which can affect communications and weather here on Earth.

Solar maximum or solar max is the period of greatest solar activity in the solar cycle of the sun. During solar maximum, sunspots appear. Solar maximum is contrasted with solar minimum. Solar maximum is the period when the suns magnetic field lines are the most distorted due to the magnetic field on the solar equator rotating at a slightly faster pace than at the solar poles. The sun takes about 11 years to go from one solar maximum to another and 22 years to complete a full cycle (where the magnetic charge on the poles is the same).

The Sun, a roiling ball of plasma, occupies its place in space approximately 93 million miles from Earth. Though it seems simple to inhabitants of this planet -- the Sun shines, giving light and heat -- the processes occurring in the Sun are so complex that many scientists devote their careers to just one aspect of solar activity.

Changes in the activity of the Sun particularly engage solar scientists. Whether fluctuations in the solar magnetic field, expulsions of plasma called coronal mass ejections, emissions of high-energy flares, or changes in the sunspot number, variations in solar activity can be dramatic and therefore highly interesting.

Through careful study of solar activity (particularly sunspots, visible from Earth through telescopes) over hundreds of years, scientists have found a consistent cycle of activity: every eleven years, activity rises to a maximum, then falls to a minimum. To track the solar cycle, scientists plot the average of Wolf numbers (values from a method of counting sunspots devised by Johann Rudolf Wolf in 1848) from various observatories daily to get a sunspot number graph.

The sunspot or solar cycle does not have the same magnitude every eleven years, however. Entire cycles can have lower activity levels than usual, as during the Maunder Minimum from 1645 to 1700, or the upcoming maximum might have more activity than ever.

Sunspots at Solar Maximum and Minimum

These images from the Solar and Heliospheric Observatory (SOHO) spacecraft compare sunspots on the Sun’s surface (top row) and ultraviolet light radiating from the solar atmosphere (bottom row) at the last solar maximum (2000, left column) and at the current solar minimum (2009, right column.) The sunspot images were captured by the Michelson Doppler Imager (MDI) using filtered visible light. On March 18, 2009, the face of the Sun was spotless.
The other set of images, acquired by the Extreme Ultraviolet Imaging Telescope (EIT), shows ultraviolet light radiating from the layer of the atmosphere just above the Sun’s surface. This part of the solar atmosphere is about 60,000 Kelvin—a thousand times hotter than the surface of the Sun itself. On July 19, 2000, the solar atmosphere was pulsating with activity: in addition to several extremely bright (hot) spots around the mid-latitudes, there were also numerous prominences around the edge of the disk. On March 18, 2009, however, our star was relatively subdued.

Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715 . Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past. The connection between solar activity and terrestrial climate is an area of on-going research. It is named after the solar astronomer Edward W. Maunder (1851–1928) who studied changes of sunspots latitudes in different times and also during second part of 17th Century.

The Dalton Minimum 

The Dalton Minimum was a period of low solar activity, named for the English meteorologist John Dalton, lasting from about 1790 to 1830. Like the Maunder Minimum and Spörer Minimum, the Dalton Minimum coincided with a period of lower-than-average global temperatures. The Oberlach Station in Germany, for example, experienced a 2.0° C decline over 20 years. The Year Without a Summer, in 1816, also occurred during the Dalton Minimum.

There have been several other less dramatic dips in the level of solar activity, in terms of sunspot counts, over time. These include  Spörer Minimum (1450 to 1540), Wolf Minimum (1280 to 1340), and Oort Minimum (1010 to 1050). Based on evidence other than direct observations of sunspot counts, in total there seem to have been 18 periods of sunspot minima in the last 8,000 years, and studies indicate that the Sun currently spends up to a quarter of its time in these minima. There have also been periods of enhanced solar activity in terms of greater sunspot counts. The Medieval Maximum lasted from about 1100 to 1250, and roughly corresponds to an extended warm period of Earth's (or maybe just Europe's) climate called the Medieval Warm Period that lasted from the 10th to the 14th century... further fueling speculation about possible links between solar activity and Earth's climate.

February 17 2008-NASA and European Space Agency satellite images have captured the appearance of the first sunspot of the new solar cycle. Sunspots are areas of intense magnetic activity that are visible on the surface of the Sun as dark spots. Sunspot activity rises and falls on a roughly 11-year cycle. The previous solar cycle peaked between 2000 and 2002. Even as scientists kept an eye on the sunspot “stragglers” of waning Solar Cycle 23 in late 2007, they were also on the lookout for the first sunspot that would signal the start of Solar Cycle 24.
On January 4, 2008, the new sunspot—about the width of the Earth, but small by Sun standards—appeared in the Sun’s Northern Hemisphere, with its north magnetic pole (red area) pointing to the right and its south magnetic pole (blue) pointing to the left. The image was captured by the Solar and Heliospheric Observatory satellite. The sunspot lasted until January 6 before fading away. The animations above show activity between January 1-14.
The position of the magnetic poles in sunspot 10981 was one of the ways scientists knew it was part of a new cycle. Within any particular cycle, the sunspots in each hemisphere will have opposite polarity, and the polarity for each hemisphere reverses from cycle to cycle. Since the large sunspot area in the Southern Hemisphere from Solar Cycle 23 (number 10980, shown in the left-hand part of the image) is also oriented with its north pole at right and south pole at left, the new one that appeared in the Northern Hemisphere on January 4 must be part of a different solar cycle.
The other criteria that let scientists know that spot 10981 was part of a new cycle was its location on the face of the Sun. The first sunspots of a new solar cycle always appear in the higher latitudes of both hemispheres. As the cycle matures, the sunspots get closer and closer to the equator. When scientists graph the latitude of sunspots over the course of many solar cycles, the result is a sequence of symmetrical shapes that they refer to as a “butterfly diagram.” Butterfly diagrams also show how the last sunspots of older cycles occur at the same time as the first sunspots of new cycles, just as sunspots from Solar Cycles 23 and 24 overlap in the image.
The area of the Sun affected by sunspots varies from cycle to cycle (final graph) and depends on the number and size of the spots. Solar Cycle 19 (second peak from left), which began in 1954 and peaked in 1957, is the record holder for most active solar cycle, with 201 sunspots. Higher numbers of sunspots make major solar storms more likely. Solar storms can interfere with power grids, aircraft navigation and communication systems, and satellites. The panel of scientists who issue forecasts for the Space Environments Center at the National Oceanic and Atmospheric Administration was evenly spilt about the prospects for Solar Cycle 24. About half the panelists thought it would be a moderately strong cycle, with about 140 sunspots, and the other half thought it would be moderately weak, with about 90 sunspots.