Again, there are two parts for this question. The modern Scientific Answer and the older Astronomical Answer:

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Sunspot Cycle from 1995 to the present.
http://science.nasa.gov/headlines/y2009/images/deepsolarminimum/ssn_predict_l_strip.gif

Great Solar Cycle has been known since the mid-1800s. The cycle represents a period in which the Sun exhibits Sunspot activity; these are "islands" of magnetism the size of the Earth on the surface of the sun. Sunspots are the source of solar flares, coronal mass ejections and intense UV radiation. When sunspot counts were first plotted, "peaks" of solar activity were found. These peaks are followed by "valleys" of relative calm, a timely clockwork pattern that has persisted for more than 200 years. We are watching the finishing process of Cycle 23 and entering Cycle 24, perhaps in the next couple of years around 2011.

The Sunspot numerical graph that represents the cycle goes up and down during an 11-year period. Cycles vary in length from 9 to 14 years. Some "peaks" are high, others are low. The "valleys" are usually brief and they last just a couple of years, but sometimes they stretch out longer. Predicting the "peaks" and "valleys" has proven difficult. In the 17th century the Sun dropped into a 70-year period of spotlessness known as the Maunder Minimum that still perplexes scientists.

Right now, the solar cycle is in a "valley" experiencing a very deep solar minimum, the deepest and quietest sun we've seen in the past century. In the last two years, the sun set Space Age records for low Sunspot counts, more than two years without a significant solar flare. There were no Sunspots observed on 266 of the year's 366 days (73%). This means a low solar irradiance and weak solar wind with almost 20% drop in pressure since the mid-1990 (the lowest since these measurements began in the 1960s). The solar wind helps keep galactic cosmic rays out of the inner solar system. With the solar wind flagging, more cosmic rays enter, resulting in increased health hazards for astronauts.

Plot of Sunspot numbers with measured peak of the last solar cycle (blue line) and the predicted peak of the next solar cycle (red line).
http://science.nasa.gov/headlines/y2009/images/noaaprediction/prediction_strip2.jpg

The "valleys" are usually brief and they last a couple of years sometimes stretching longer. In the 17th century the sun had a period without spots known as the Maunder Minimum. Researchers believe upcoming Solar Cycle 24 will be similar to the cycle that peaked in 1928, marked by a red arrow.
http://science.nasa.gov/headlines/y2009/images/noaaprediction/maunderminimum.jpg

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Ancient Egyptians believed in the law of Maat, the cosmic order, which came to Earth directly from the Gods at the time of creation at a place called Heliopolis, where the cosmic phoenix alighted on the Primeval Mound and set in motion the time, the cycles of the Sun, Moon and the Stars. According to their believes the first sunrise took place here.

After generation of sky observations the astronomers priests at Heliopolis worked out the mechanism, the code, of the cosmic order and how to regulate events on Earth such the flooding of the Nile.

They concluded that the Earth was governed by six basic cycles, three short term and three long term. These cycles measured in day or years were:

Short Term Cycles:

1 day: Solar day
365 days: Solar cycle, the Solar/tropical year less than 0.243 day
365.25 days: Sothic year, the period between two heliacal rising of Sirius

Long Term Cycles:

1.460 years: Sothic cycle, return of New Year´s Day with the heliacal rising of Sirius
1.506 years: Great Solar Cycle; return of New Year´s Day with the summer solstice
26.000 years: precession cycle or Great Year

Because they did not take into account the 0.243 day difference with the true solar year, they registered a similar but long term solar cycle of 1.506 years (the Great Solar Cycle) with respect of the summer solstice and another long term cycle of 1.460 year with respect to the heliacal rising of Sirius.