Allan Kardec de Almeida Jr.

arXiv2026

Assessment of sky brightness in central Portugal: the Dark Sky destination "Aldeias do Xisto" case study

A combination of remote sensing techniques, open space data and field testing was developed to derive astronomical and meteorological parameters and assess Dark Sky brightness of the hitherto unstudied Schist Villages region in the mountainous Interior Center of Portugal. This study covered the period 2012-2017 and established the methodology for regular light pollution and sky brightness studies in the region using satellite imagery to reduce cost and time and increase accuracy of the final analysis. Long-term Artificial Light At Night (ALAN) data from VIIRS instrument aboard the Suomi-NPP satellite along with cloud cover inferred from MODUS/AQUA satellite data and orographic data, were analyzed in a Geographical Information Systems (GIS) environment. The derived ALAN values were consistent with a preliminary site survey selection, confirming the accuracy of the identified dark sky spots in the region. The analyzed region area spans 1624 Km$^2$ and the darkest site within it showed a sky brightness of 21.4 mag/arcsec$^2$. Ground-based SQM photometer observations of the Night Sky Brightness (NSB) at the zenith validated the satellite derived ALAN data. The devised field testing is itself a low cost solution that can be used by teams in developing countries to easily assess dark sky potential prior to the development of local observatories and astro-tourism activities. This study supported the initial certification of this region as a Dark Sky Starlight Tourist Destination since 2018, an important milestone for dark sky protection in central Portugal.

astro-ph.IM↗

arXiv2026

Dynamical Behavior and Surface Features of Large Super-Fast Rotator Near-Earth Asteroid (436724) 2011 UW158

The sub-kilometer Super-Fast Rotator and Potentially Hazardous Asteroid (436724) 2011 UW158 exhibits an extreme dynamical environment driven by its rotational period of 0.61072 h. Using a 3-D polyhedral shape model, we investigate the surface dynamic stability under both cohesionless and cohesion-modified conditions, while also addressing families of periodic orbits, station-keeping maneuvers, and energy states in this rapidly rotating, irregular-body regime. Our results show that, with the inclusion of cohesion, the effective slopes decrease to ~45°, permitting the retention of boulders with maximum sizes of ~50 m near the equatorial region. The dominance of the centrifugal term in the effective potential shifts the exterior equilibrium points inward, creating highly unstable geopotential regions where loose regolith is susceptible to ejection, preventing long-term surface retention outside the polar regions. To quantify this instability, we introduce the equivalent instability speed ($v_{\mathrm{ei}}$), extending conventional escape speed analyses to the SFR regime. These results are consistent with significant internal cohesion in 2011 UW158, which enables the body to maintain structural integrity under rotational stresses exceeding the classical spin barrier. Additionally, thermophysical modeling reveals that the super-fast rotation produces a nearly uniform surface temperature distribution. Finally, we apply a spherical harmonics method to compute families of periodic orbits around the asteroid to assess the fuel cost of station-keeping maneuvers at reduced computational cost. Overall, this study characterizes the dynamical environment of 2011 UW158, contributing to the understanding of Super-Fast Rotator asteroids recently identified in LSST survey images.

astro-ph.EP↗