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.
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). The combination of sunspots and their grouping is used because it compensates for variations in observing small sunspots.
This number has been collected and tabulated by researchers for over 150 years. They have found that sunspot activity is cyclical and reaches its maximum around every 9.5 to 11 years (note: Using data from SIDC for the last 300 years and running a FFT function on the data gives an average maximum at 10.4883 years/cycle). This cycle was first noted by Heinrich Schwabe in 1843.
The relative sunspot number is computed using the formula (collected as a daily index of sunspot activity):
where
- is the number of individual spots,
- is the number of sunspot groups, and
- is a factor that varies with location and instrumentation (also known as the observatory factor or the personal reduction coefficient ).
Famous quotes containing the words wolf and/or number:
“‘O opportunity! thy guilt is great,
‘Tis thou that execut’st the traitor’s treason;
Thou set’st the wolf where he the lamb may get;
Whoever plots the sin, thou point’st the season;
‘Tis thou that spurn’st at right, at law, at reason;
And in thy shady cell, where none may spy him,
Sits Sin to seize the souls that wander by him.”
—William Shakespeare (1564–1616)
“Of all reformers Mr. Sentiment is the most powerful. It is incredible the number of evil practices he has put down: it is to be feared he will soon lack subjects, and that when he has made the working classes comfortable, and got bitter beer into proper-sized pint bottles, there will be nothing left for him to do.”
—Anthony Trollope (1815–1882)