Stellar activity and variability in Young Stellar Objects (YSOs) influences our ability to accurately constrain both the fundamental stellar parameters and the activity level of the stellar surface, which in turn hamper the characterization of planetary atmospheres. Magnetic fields at the stellar surface can be strong enough to block convection, generating large cool starspots that emit at temperatures colder than the photosphere. Because of this, optical-near infrared spectra of these systems are a complex synthesis of multiple components. In addition to the previously considered stellar photospheres and chromospheres, stellar and disk winds, and circumstellar accretion and disks, a recently recognized component is starspots. Quantifying the spectral contributions from any of these processes requires us to disentangle the complicated multicomponent emission. Here we present results from spectral modeling of sixty accreting and non-accreting YSOs ($\leq$25 Myr) across four star forming regions. We find the spectra to be best fit by two-temperature models that include both standard stellar photospheres and spots with spot filling factors ranging between 0.2 and 0.9 with spot temperatures 1000 K cooler than the photosphere in the median. Such results have significant impacts on measurements of effective temperatures, which in turn alter the masses, ages, and inferred mass accretion rates. For a sub-sample of fifty stars with magnetic field and surface gravity measurements from high resolution spectroscopy, we look for a correlation between starspot filling factors and stellar magnetic field, finding no such correlation. These results highlight the importance of starspots as a measure of stellar magnetic activity.

This work revisits the possible influence of solar activity on unexplained terrestrial events during the early years of World War II. By comparing records of major geomagnetic storms with contemporary news archives, we identified several explosions and communication failures that occurred between 1938 and 1941. Among these, the geomagnetic superstorm of September 17–19, 1941, stands out as an exceptional case: triggered by a large sunspot group and intense solar flare activity, it produced global magnetic disturbances (K-index 9) and widespread auroras visible as far south as New Mexico. Several unexplained detonations in Europe and North America were reported within hours of the storm’s peak, suggesting a possible physical link between solar-induced electrical currents and accidental explosions in sensitive wartime materials. While causality cannot be conclusively demonstrated, the temporal correspondence and physical plausibility support the hypothesis that space weather may have influenced certain wartime incidents traditionally attributed to sabotage. This historical analysis underscores the importance of integrating solar and geophysical research to better understand how extreme space weather can affect technological systems, both past and present.