Rudolf Wolf, director of the Zürich Observatory around mid-19th century, defined for the first time the sunspot number index after collecting sunspot observations made by astronomers in the two previous centuries, approximately, before that time. Based on this work of Wolf and sunspot group records made by other observers, Hoyt and Schatten (1998) published the group sunspot number index, including observations made in the 17th century (unlike the reconstruction by Wolf). The last large revision of sunspot group number was carried out by Vaquero et al. (2016). These authors based their works in the previous efforts made by Wolf and Hoyt and Schatten (1998) correcting some problematic observations included in those databases and incorporating new records both in the historical period and subsequent 1998 until 2010. Here, a proposal for improving the next version of the sunspot group number database is presented. It includes, for example, the revisions of the sunspot group counting published in recent studies from the historical observations made by Scheiner in the earliest period of the telescopic era and those made by Eimmart and Tevel during the Maunder Minimum and the Dalton Minimum, respectively. Moreover, it is also proposed the incorporation of records not included in Vaquero et al. (2016) database such as those made in the Sacramento Peak Observatory for the period 1947 – 2004. These works are framed in the ongoing global effort to improve the weakness of the sunspot number database and to recalibrate the sunspot number indices.
Hoyt, D.V., Schatten, K.H.: 1998, Group sunspot numbers: a new solar activity reconstruction. Solar Phys. 179, 189. DOI: 10.1023/A:1005007527816.
Vaquero, J.M., Svalgaard, L., Carrasco, V.M.S., Clette, F., Lefèvre, L., Gallego, M.C., Arlt, R., Aparicio, A.J.P., Richard, J.-G., Howe, R.: 2016, A Revised Collection of Sunspot Group Numbers, Sol. Phys. 291, 3061. DOI: 10.1007/s11207-016-0982-2.