Phrase guide
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noun
A measure of the number of sunspots and groups of sunspots present on the surface of the Sun.
Definition source: English Wiktionary via Wiktextract
No example sentence was provided for this meaning.
Synonyms: sunspot number, Zürich number
Antonyms: none provided
History
The idea of compiling the information about the sunspot number from various observers originated with Rudolf Wolf in 1848 in Zürich, Switzerland.
