Comparison Analysis of Starspots and Historical Sunspot Data

Dark regions commonly appearing on the Sun’s surface are known as “sunspots.” These areas of solar activity are a result of cooled regions of magnetic flux within the Sun’s photosphere. Areas of higher solar-magnetic activity heat regions of both the photosphere and chromosphere, leading to a rise in magnetic flux (Φ) to the upper regions of the Sun. The lower, cooler areas of flux within the photosphere are what are ultimately viewed as the dark “sunspots” on the Sun (National Oceanic and Atmospheric Administration, 2024, Ret. April 29, 2024). While the specific heliophysics behind the formation, evolution, and eventual decay of sunspots is not currently fully understood, extensive historical documentation of the number of sunspots present on the Sun exists and dates back to the 18th century (Royal Observatory of Belgium, 2015, Ret. April 29, 2024). Historical sunspot number (SSN) data have been used to assert the cyclic nature of the presence of sunspots on the Sun, similar to the well-understood cyclic nature of the Sun’s activity via the 11-year Schwabe Cycle and 90-year Gleissberg Cycle.

Sunspots that occur on stars other than our own Sun are commonly referred to as “starspots.” Our current understanding of starspots leads us to believe that they occur and behave similarly to their Sun-counterpart. Their detection and cycle lengths, however, vary greatly from the present methodology of documenting sunspots.

This thesis outlines the similarities and differences between sunspots and detected starspots on stars similar in type to the Sun (Le Mouël, Lopes, & Courtillot, 2020, Ret. April 29, 2024). A comparison analysis of sunspots’ and starspots’ physical characteristics and detection methodologies is also included. Present-day exoplanet detection often requires the use of these methodologies, leading to a stark overlap in exoplanet and starspot research. This thesis provides additional information on the ongoing dynamic between sunspot research and exoplanet identification. Finally, the comparison of type, detection, and background of sunspots and starspots reveals the presence of other solar activity on stars similar in type to the Sun. Future study through repeated extensive observations will likely be required to make definitive claims about the nature of starspots present on the surface of main sequence stars similar to the Sun. The documented success of present starspot detection methodologies is, however, promising for prospective research on the topic of starspots.