Active regions can be used as a diagnostic of the sub-photo-spheric activity. In this review I will discuss how the physical conditions in the subsurface layers of the Sun form and modify the three dimensional complex of the active region. Many characteristics of active regions are related to the conditions under which magnetic ux tubes are generated and to their evolution as they rise in the s...

The purpose of this letter is to address a blind-spot in our knowledge of solar active region statistics. To the best of our knowledge there are no published results showing the variation of the Mount Wilson magnetic classifications as a function of solar cycle based on modern observations. We show statistics for all active regions reported in the daily Solar Region Summary from 1992 January 1 ...

Recent satellite measurements of the solar total irradiance (S) indicate that on time scales of days to months the solar constant varies by a few tenths of a percent. The predominant part of these variations can be explained by blocking of the upward solar flux by sunspots. The observations are consistent with current theoretical models of energy storage in which the energy blocked by the sunsp...

Resonance scattering has often been invoked to explain the disagreement between the observed and predicted line ratios of Fe XVII λ15.01 to Fe XVII λ15.26 (the “3C/3D” ratio). In this process photons of λ15.01, with its much higher oscillator strength, are preferentially scattered out of the line of sight, thus reducing the observed line ratio. Recent laboratory measurements, however, have foun...

We present a comprehensive study of accretion activity in the most underdense environments in the universe, the voids, based on the SDSS DR2 data. Based on investigations of multiple void regions, we show that Active Galactic Nuclei (AGN) are definitely common in voids, but that their occurrence rate and properties differ from those in walls. AGN are more common in voids than in walls, but only...