sunspot number
sunspot index

This smoothed sunspot number might it the least active cycle in the past two hundred years.

This is an 11-year fluctuation in sunspot numbers.

Starting with Wolf, solar astronomers have found it useful to define a standard sunspot number index, which continues to be used today.

Sunspot numbers over the past 11,400 years have been reconstructed using dendrochronologically dated radiocarbon concentrations.

"On a method of investigating periodicities in disturbed series, with special reference to wolfer's sunspot numbers".

The maximum usable frequency for skywave propagation is strongly influenced by sunspot number.

By the 19th century, there was a long enough record of sunspot numbers to infer periodic cycles in sunspot activity.

The relative sunspot number is computed using the formula (collected as a daily index of sunspot activity):

The sun's cycles of activity last about 11 years from peak to peak; sunspot numbers are now decreasing and will continue to do so until about 1997.

We care about this because sunspot numbers act as a proxy for the amount of radiation sent out by the sun, which can have a significant influence on the Earth's climate.

The maximum smoothed sunspot number (monthly number of sunspots averaged over a twelve-month period) observed during the solar cycle was 86.5, and the minimum was 11.2.

These cosmic rays are responsible for the production of the radioactive isotopes of carbon and beryllium mentioned above, which is why we can use them to track sunspot numbers.

One example of possible correlations between factors affecting the climate and global events, popular with the media, is a 2003 study on the correlation between wheat prices and sunspot numbers.

The Gnevyshev-Ohl rule is an empirical rule according to which the sum of sunspot numbers over an odd cycle exceeds that of the preceding even cycle.

Measurements of the radiative output, or solar constant, seem to justify the first assumption, and the record of periodicity in sunspot numbers is taken as evidence of the second.

The idea of computing sunspot numbers was originated by Rudolf Wolf in 1848 in Zurich, Switzerland and, thus, the procedure he initiated bears his name (or place).

During the late spring and most of the summer, regardless of sunspot numbers, afternoon short band openings into small geographic areas of up to 1500 km occur due to Sporadic-E propagation.

Various studies have been made using sunspot number (for which records extend over hundreds of years) as a proxy for solar output (for which good records only extend for a few decades).

STEREO and SOHO observed CME rate versus the Sunspot number (PNG plot) / (text version)

German Amateur astronomer Heinrich Schwabe, who has been studying the Sun for the past 17 years, announces his discovery of a regular cycle in sunspot numbers - the first clue to the Sun's internal structure.

The investigations of the Maunders demonstrated a correlation between the variation in sunspot numbers and the climate of the Earth, leading to the discovery that the decrease period of solar activity during the Maunder Minimum likely resulted in the Little Ice Age.

Solar irradiance fluctuations have been proposed as a possible explanation for these discrepancies, and various solar properties (for example, radius, smoothed sunspot number or cycle length) have been suggested as proxies for solar irradiance variations in the absence of direct data.

The Wolf number (also known as the International sunspot number, relative sunspot number, or Zürich number) is a quantity that measures the number of sunspots and groups of sunspots present on the surface of the sun.

Wolf number sunspot index displays various periods, the most prominent of which is at about 11 years in the mean.

Sunspot index graphics, Solar Influences Data Analysis Center (retrieved 27 September 2007).