DOI: 10.5281/zenodo.14866344
title: Sunspot Group Database of the Specola Solare Ticinese

description: Content:

The database contains data for each sunspot group observed and recorded at the Specola Solare Ticinese from 01.06.1957 until 31.12.2024. 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. 

 

 
description: Acknowledgments: This work has been possible thanks to the financial support by the Federal Office of Meteorology and Climatology MeteoSwiss, in the framework of GCOS Switzerland, by Canton Ticino through the Swisslos Fund and by the Wolf Foundation. The authors would like to thank ETH Zurich University Archives and the DigiCenter for the collaboration in this project, in particular Evelyn Boesch and Christian Huber. The authors acknowledge the support of the staff of the SILSO data center by providing the Digisun software and advice, in particular to Frédéric Clette and Sabrina Bechet. The database WEB interfaces for the project were developed with the collaboration of Christian Skorski and Bruno Barbieri. This work would not have been possible without all patient observations made by the Sunspot observers at Specola. In particular the authors would like to dedicate this work to the main past observer Sergio Cortesi (1932-2021).