5321 20230106163501.0 10.1007/978-1-4939-2584-1 DOI BKSECT-2021-0002 Clette, F. Revisiting the Sunspot Number. A 400-Year Perspective on the Solar Cycle 2015 69 STCE Sunspots Solar cycle Solar activity Space climate Svalgaard, L. Vaquero, J.M. Cliver, E.W. The Solar Activity Cycle Space Sciences Series of ISSI, Springer 978-1-4939-2583-4 35--103 frederic.clette@observatoire.be https://www.springer.com/gp/book/9781493925834 https://link.springer.com/chapter/10.1007%2F978-1-4939-2584-1_3 BOOKSECT