Sunspot Group Database of the Specola Solare Ticinese

Content: The database contains data for each sunspot group observed and recorded at the Specola Solare Ticinese from 01.06.1957 until 31.12.2025. Recorded for each group are the date and time of observation, code for the observer, the sky quality during observation, the incremental number, the weighted count, the unweighted count (if available), the Zurich classification, the latitude and longitude determined with Digisun (a free software developed by SILSO for measuring and recording sunspot groups features) or, if these are not available, the latitude and longitude determined manually with the Stonyhurst solar disk, the ETHZ signature, and the DOI code of the drawing. Context: The daily sunspot drawings are performed at Specola Solare Ticinese since 1957. Between 1957 and 1980 Specola was the southern observing station belonging to the Eidgenössische Sternwarte of ETH Zurich (director prof. Max Waldmeier). Since 1981 Specola is operated independently by the local Associazione Specola Solare Ticinese. The corresponding sunspot drawings up to 2019 are archived at the ETH-Zurich University Archives with codes HS1304.5 (1957-1980) and HS1304.6 (1981-2019). They are also available in digital format on the platform e-manuscripta ( https://www.e-manuscripta.ch/). The sunspot drawings made after 2020 are archived at Specola Solare Ticinese and the digital version is made available on the site https://sunspots.irsol.usi.ch/. The main purpose of the drawings is to determine the relative number (R) of the solar activity (called also Wolf number or Sunspot Number). In this context the Specola is considered as the pilot station by the world data center SILSO (Sunspot Index and Long-term Solar Observations) in Bruxelles, whose main goal is the production, preservation and dissemination of the international sunspot number. The relative number is calculated according to the formula R = k.(10.g+f) introduced by Rudolf Wolf, where g is the number of sunspot groups, f the number of sunspots and k is a reduction factor which depends from the observer, the instrument and the observing conditions. The drawings are always performed with the white light projection method (diameter of the Sun image 250 mm) according to the Zurich standard. A Zeiss Coudé refractor is used (D/f 150/2250 mm baffled at 8 cm). The drawings are oriented with a precision of ±1° with respect to the heliographic axis. When the seeing is good enough (most of the cases), the quality of the sunspot drawings details is accurate and can be used for the morphological analysis of sunspot groups and for the determination of their heliographic position. The obtained image is specular: heliographic North above and eastern limb on the right. For more information: https://www.specola.ch/en/sunspot-drawings-of-the-specola-solare-ticinese/sunspot-drawings-of-the-specola-solare-ticinese All observations can be found here: https://sunspots.irsol.usi.ch/ Columns explanation: date Observation date time Observation time (UT) observer Observer identifier, according to following list Sergio Cortesi: 1 Edy Alge: 2 Elena Altoni: 3 Michele Bianda: 4 Araldo Pittini: 5 Andrea Manna: 6 Renzo Ramelli: 7 Marco Cagnotti: 8 Anna Cairati: 9 Roberto Cortesi: 10 Michele DeLorenzi: 11 Marco Cortesi: 12 J. Jzsák: 13 Rolf Schmid: 14 seeing (SIDC) Quality of the sky during the observation (5=best, 1=very bad) group nr Incremental sunspot group number (starting from the beginning of the year) spot count Unweighed sunspot counting weighted spot count Weighted sunspot counting following the Waldmeier's rule Cortesi, S., Cagnotti, M., Bianda, M. et al. Sunspot Observations and Counting at Specola Solare Ticinese in Locarno Since 1957. Sol Phys 291, 3075–3080 (2016). https://doi.org/10.1007/s11207-016-0872-7 https://link.springer.com/article/10.1007/s11207-016-0872-7 type Zurich classification of the sunspots group latitude Heliographic group floating point precision latitude (±1°) determined with DigiSun software longitude Heliographic group floating point longitude (±1°) determined with DigiSun software manual latitude Heliographic group integer latitude (±1°) detetermined manually with Stonyhurst solar disk manual longitude Heliographic group integer longitude (±1°) with Stonyhurst solar disk ETHZ signature Drawing-specific signature of the ETH Zurich University Archive URL URL of the digitized sunspot drawing file.