Sky Brightness Research Articles

Measurement of the Quality of the Night Sky as A Feasibility Study for Astronomy Tourism Using A Sky Quality Meter at Jurang Senggani Campground, Tulungagung Regency, East Java

Measurement of the sky’s brightness at night is needed in observatories of celestial bodies. This research utilizes tourism in Tulungagung Regency to increase tourist attraction to the beauty of celestial objects such as stars, moon, etc. In addition, it provides information to astronomical tourism whether or not the place is suitable for research. This study measures the sky’s brightness at a certain time based on the region and position of the moon. The method used is observation using Sky Quality Meter. The places used are the Senggani Jurang Campground, Tulungagung Regency. This study was conducted for 16 days using SQM-L and SQM-LU which were performed every 10 minutes. The data obtained from the observations will then be analyzed using correlation between time and the value of sky brightness with MPSAS (Magnitude Per Square ArcSecond) units. This research results show that the best sky brightness value is 22.79 MPSAS. It shows that on average throughout the night light pollution is very little. From the results of the observation data that has been done, it can be said that the Senggani Jurang Campground, Tulungagung Regency has the potential to become astronomical tourism.

Faster Detection of "Darks" than "Brights" by Monkey Superior Colliculus Neurons.

Visual processing is segregated into ON and OFF channels as early as in the retina, and the superficial (output) layers of the primary visual cortex (V1) are dominated by neurons preferring dark stimuli. However, it is not clear how the timing of neural processing differs between "darks" and "brights" in general, especially in light of psychophysical evidence; it is also equally not clear how subcortical visual pathways that are critical for active orienting represent stimuli of positive (luminance increments) and negative (luminance decrements) contrast polarity. Here, we recorded from all visually-responsive neuron types in the superior colliculus (SC) of two male rhesus macaque monkeys. We presented a disk (0.51° radius) within the response fields (RFs) of neurons, and we varied, across trials, stimulus Weber contrast relative to a gray background. We also varied contrast polarity. There was a large diversity of preferences for darks and brights across the population. However, regardless of individual neural sensitivity, most neurons responded significantly earlier to dark than bright stimuli. This resulted in a dissociation between neural preference and visual response onset latency: a neuron could exhibit a weaker response to a dark stimulus than to a bright stimulus of the same contrast, but it would still have an earlier response to the dark stimulus. Our results highlight an additional candidate visual neural pathway for explaining behavioral differences between the processing of darks and brights, and they demonstrate the importance of temporal aspects in the visual neural code for orienting eye movements.SIGNIFICANCE STATEMENT Objects in our environment, such as birds flying across a bright sky, often project shadows (or images darker than the surround) on our retina. We studied how primate superior colliculus (SC) neurons visually process such dark stimuli. We found that the overall population of SC neurons represented both dark and bright stimuli equally well, as evidenced by a relatively equal distribution of neurons that were either more or less sensitive to darks. However, independent of sensitivity, the great majority of neurons detected dark stimuli earlier than bright stimuli, evidenced by a smaller response latency for the dark stimuli. Thus, SC neural response latency can be dissociated from response sensitivity, and it favors the faster detection of dark image contrasts.

A Note from the Editor

A Note from the Editor Susanne Shawyer Every summer I take a break from my regular commitments to reflect on the past academic year and to anticipate the months to come. My summer rest provides a welcome opportunity to assess my contributions as a theatre scholar, artist, and educator, and to consider the ways I would like to grow in the future. This year, my annual reflection feels more urgent than ever. The global pandemic persists. The climate crisis grows with frequent wildfires and record heat. In the United States, gun violence continues. Colleagues are burnt out. Students are anxious. Why do we continue to make theatre? How can performance scholarship benefit our communities? What is the value of art in times of crisis? This year I find answers to those questions not in the studio or on stage, but in the natural world. I watch with fascination as a spider busily spins its web outside my window. I hearken to the shrill song of cicadas, the gentle chirping of songbirds. I touch the rough bark of an oak tree and inhale its warm scent. Action. Music. Spectacle. As I connect to the natural performances around me, I am comforted. Bright blooms offer hope and a promise of renewal. Sticky summer air recalls other compelling outdoor performances. A Shakespeare in the Park interrupted by a sudden thunderstorm. A jingle dress dance at a powwow under bright blue sky. A giant puppet parade. A block party. These examples remind me of what I value most in performance: community, surprise, joy. What you value may differ. You may find your answers elsewhere, perhaps in a fresh cup of coffee, a lunch with friends, a new book, or a darkened auditorium. I hope that you can take some time while reading this issue of Theatre Topics to reflect on what you value and how you would like to grow in the year ahead. How can your theatre scholarship, artistry, or pedagogy reflect what matters most to you, your students, and your community? The articles and notes in this issue take up this question. They offer detailed and specific examples of how theatre-makers respond to the urgent demands of their communities while at the same time engaging with what they treasure most about performance. They reflect on what we have learned from the past few years, consider what we should keep, and advocate for what we can change. Each piece in this issue is a thoughtful meditation on the value of theatre in times of crisis. First, Mary Anderson and Richard Haley explore the "circumstantial aesthetics" of Michigan Opera Theatre's pandemic production of Twilight: Gods in a parking garage. They argue that the literal and metaphorical pandemic "bubbles" at play in this drive-through opera created a new mode of audience engagement, as drivers became co-producers in the autopoietic process of performance. As they reflect on the pleasure and pain that participatory theatre arouses in spectators, Anderson and Haley contend that innovative aesthetic experiments like this drive-through production can usefully reconfigure "our sense of time, space, and place." Using Michigan Opera Theatre's creative staging as a case study for pandemic ingenuity, the authors ask the reader to consider the aesthetic possibilities that crisis circumstances can inspire. In "Effective Dreaming in the Time of Zoom Theatre: Reflections on Directing The Lathe of Heaven," Isaiah Matthew Wooden explores insights gained from a pandemic pivot to Zoom theatre. Using a case study of a performance at Brandeis University in 2021, his article outlines how the pandemic demanded creative thinking that yielded rich discoveries about the production process. Questioning each step—from season selection to rehearsal norms, from technical decisions to finding [End Page vii] opportunities to collaborate—allowed Wooden to reconnect to his theatrical and pedagogical values and find fresh approaches to his artistic process. These new insights not only transformed his artistry and pedagogy during a time of crisis, but also offer the reader new ways of making theatre in our transforming world. In her note from the field, Ayshia Mackiestephenson describes her pedagogical One Love Method, created to empower students, encourage antiracist allyship, and resist white supremacy in higher education...

Long-term trends of light pollution assessed from SQM measurements and an empirical atmospheric model

ABSTRACT We present long-term (4–10 yr) trends of light pollution observed at 26 locations, covering rural, intermediate, and urban sites, including the three major European metropolitan areas of Stockholm, Berlin, and Vienna. Our analysis is based on (i) night sky brightness (NSB) measurements obtained with sky quality metres (SQMs) and (ii) a rich set of atmospheric data products. We describe the SQM data reduction routine in which we filter for moon- and clear-sky data and correct for the SQM ‘aging’ effect using an updated version of the twilight method of Puschnig et al. (2021). Our clear-sky, aging-corrected data reveal short- and long-term (seasonal) variations due to atmospheric changes. To assess long-term anthropogenic NSB trends, we establish an empirical atmospheric model via multivariate penalized linear regression. Our modelling approach allows to quantitatively investigate the importance of different atmospheric parameters, revealing that surface albedo and vegetation have by far the largest impact on zenithal NSB. Additionally, the NSB is sensitive to black carbon and organic matter aerosols at urban and rural sites, respectively. Snow depth was found to be important for some sites, while the total column of ozone leaves impact on some rural places. The average increase in light pollution at our 11 rural sites is 1.7 per cent per year. At our nine urban sites, we measure an increase of 1.8 per cent per year and for the remaining six intermediate sites we find an average increase of 3.7 per cent per year. These numbers correspond to doubling times of 41, 39, and 19 yr. We estimate that our method is capable of detecting trend slopes shallower/steeper than ±1.5 per cent per year.

Artificial light at night correlates with seabird groundings: mapping city lights near a seabird breeding hotspot.

Artificial light at night (ALAN) is a growing conservation concern for seabirds, which can become disoriented and grounded by lights from buildings, bridges and boats. Many fledgling seabirds, especially Procellariiformes such as petrels and shearwaters, are susceptible to light pollution. The Hauraki Gulf, a seabird hotspot located near Tāmaki Makaurau/Auckland, Aotearoa—New Zealand’s largest urban city, with a considerable amount of light pollution and regularly documented events of seabird groundings. We aim to identify the characteristics of locations especially prone to seabird groundings. We used an online database of seabirds taken to a wildlife rescue facility by the public to map 3 years of seabird groundings and test for correlations between seabird groundings and the natural night sky brightness. We found that areas with lower amounts of natural night sky brightness and greater light pollution often had a higher number of seabirds grounded. Further, we identified important seasonal patterns and species differences in groundings. Such differences may be a by-product of species ecology, visual ecology and breeding locations, all of which may influence attraction to lights. In general, seabird groundings correlate with the brightness of the area and are species-specific. Groundings may not be indicative of human or seabird population abundance considering some areas have a lower human population with high light levels and had high amounts of seabird groundings. These findings can be applied worldwide to mitigate groundings by searching and targeting specific brightly lit anthropogenic structures. Those targeted structures and areas can then be the focus of light mitigation efforts to reduce seabird groundings. Finally, this study illustrates how a combination of community science, and a concern for seabirds grounded from light attraction, in addition to detailed animal welfare data and natural night sky brightness data can be a powerful, collaborative tool to aid global conservation efforts for highly-at-risk animals such as seabirds.

Towards an absolute light pollution indicator

The growing concern about the negative impact of artificial light at night on biodiversity and human health increases the need of defining a general indicator that could be used for characterizing light pollution as well as performing both spatial and temporal comparisons. In this paper, we show that the traditional indicators based on direct numerical measurements of sky brightness suffer from significant limitation due to calibration bias and lack of reproducibility. Furthermore, these measures are most often performed in periods of clear sky. They do not reflect the wide variety of meteorological conditions that can produce highly inhomogeneous levels of light pollution on a given site. To overcome these issues, we propose a statistical indicator called NSB Dispersion Ratio. This indicator is derived from a statistically significant number of individual night sky brightness measurements, under various meteorological conditions. It is independent of any absolute photometer calibration. It only requires on-time precise corrections of the contribution of natural light sources such as the Galactic plane.

Night-Time Skyglow Dynamics during the COVID-19 Epidemic in Guangbutun Region of Wuhan City

The COVID-19 epidemic lockdown has a direct influence on urban socioeconomic activity, including night-time light (NTL) changes. Night-time skyglow, a form of light pollution caused by NTL, is also affected by public emergencies. Here we investigated the impact of the lockdown on the night-time skyglow in the Guangbutun region of Wuhan, China. We monitored the night-time sky from 1 November 2019 to 12 April 2020 and compared the intraday skyglow pattern and day-to-day variation of skyglow before and during the lockdown. We found that the detected earliest shutdown timing of lights (STL) was moved from 22:00 (before the lockdown) to 21:30 (after entering the lockdown), and the fluctuation of skyglow decreased significantly during the lockdown. Furthermore, we found the night-time skyglow at various time intervals generally decreased and then recovered during the lockdown. The most severe decrease in zenith sky brightness (ZSB) was observed at the 21:30–22:00 time interval, with a decrease ratio (DR) of 72.1% and a recovery ratio (RR) of only 22.6%. On the other hand, the skyglow near midnight was the least affected by the lockdown, and the RR (32.6% and 24.3%) was comparable to the DR (30.4% and 38.2%), which means the skyglow at this time basically recovered to the pre-epidemic level. We conclude that long-term monitoring of sky brightness using single-channel photometers, such as SQMs, can provide a multi-temporal microscopic perspective for studying the dynamics of skyglow caused by human activities.

Defensive shimmering responses in Apis dorsata are triggered by dark stimuli moving against a bright background.

Giant honeybees, including the open-nesting Asian giant honeybee Apis dorsata, display a spectacular collective defence behaviour - known as 'shimmering' - against predators, which is characterised by travelling waves generated by individual bees flipping their abdomens in a coordinated and sequential manner across the bee curtain. We examined whether shimmering is visually mediated by presenting moving stimuli of varying sizes and contrasts to the background (dark or light) in bright and dim ambient light conditions. Shimmering was strongest under bright ambient light, and its strength declined under dim light in this facultatively nocturnal bee. Apis dorsata shimmered only when presented with the darkest stimulus against a light background, but not when this condition was reversed (light stimulus against dark background). This response did not attenuate with repeated exposure to the stimuli, suggesting that shimmering behaviour does not undergo habituation. We suggest that this is an effective anti-predator strategy in open-nesting A. dorsata colonies which are exposed to high ambient light, as flying predators are more easily detected when they appear as dark moving objects against a bright sky. Moreover, the stimulus detection threshold (smallest visual angular size) is much smaller in this anti-predatory context (1.6-3.4deg) than in the context of foraging (5.7deg), indicating that ecological context affects the visual detection threshold.

Image Dehazing Technique Based on Sky Weight Detection and Fusion Transmission

<p>Computer vision techniques are widely applied to the object detection, license plate recognition, remote sensing, and outdoor monitoring system. The performance of these applications mainly relies on the high quality of outdoor image. However, an outdoor image can be led to contrast decrease, color distortion, and unclear structure by poor weather conditions and human factors such as haze, fog, and air pollution. These issues may lower down the sharpness of a photo. Despite of the single-image dehazing is used to solve these issues, it cannot achieve a satisfactory result when the method deals with the bright scene and sky area. In this article, we aim to design an adaptive dehazing technique based on fusion transmission and sky weight detection. The sky weight detection is employed to distinguish the foreground and background, while detected results are applied to the fusion strategy to calculate deep and shallow transmissions. Thus, this can get rids of the subject of over-adjustment. Experimental results have demonstrated that the new method can outperform the latest state-of-the-art methods in terms of subjective and the objective assessments.</p> <p> </p>

Night sky brightness measurement, quality assessment and monitoring

Ground-based optical astronomy necessarily involves sensing the light of astronomical objects along with the contributions of many natural sources ranging from the Earth's atmosphere to cosmological light. In addition, astronomers have long contended with artificial light pollution that further adds to the 'background' against which astronomical objects are seen. Understanding the brightness of the night sky is therefore fundamental to astronomy. The last comprehensive review of this subject was nearly a half-century ago, and we have learned much about both the natural and artificial night sky since. This Review considers which influences determine the total optical brightness of the night sky; the means by which that brightness is measured; and how night sky quality is assessed and monitored in the long term.

Novel control system applied in the modernization of public lighting systems in heritage cities: Case study of the City of Cuenca

Several heritage cities face the need to modernize public lighting systems that are installed on the facades of buildings. The legal obstacles to intervene in heritage infrastructures create a different scenario than other cities. This circumstance raises the question if it is possible to install a modern, innovative lighting system, isolated from the electrical distribution system. This research analyzes the feasibility of modernizing the system using 304 mini photovoltaic generation plants, implementing a novel lighting system control process that indirectly uses sky brightness measurements based on current research at the Catholic University of Cuenca. As a case study, the Historic Center of the City of Cuenca-Ecuador, a World Heritage Site, whose system is made up of 1,252 luminaires, is analyzed. The results conclude that it is feasible to modernize the lighting service with the adoption of the proposed technologies and for control, a novel system based on indirect measurement of sky clarity has been developed. Finally, the political implications are analyzed in the framework of energy efficiency and modernization of the systems, as well as the recommendation to the political decision-makers. The study can be replicated in other cities of the world with similar characteristics.

The Stability of Fiber Spectrographs in the Faint-source Regime

The use of optical fibers in astronomical instrumentation offers high-multiplex and light-gathering flexibility. However, with most previous fiber spectrographs optimized for large fields of view on modest-aperture telescopes, the performance of fibers in the context of faint targets on large telescopes remains largely untested. In this paper, we evaluate aspects of fiber stability, especially as they apply in the context of precision sky subtraction of faint sources at modest spectral resolution (R ∼ 3000). After introducing a framework for describing potential systematic errors, we use publicly available data from existing instruments, including instrumentation used by the fourth-generation Sloan Digital Sky Survey’s MaNGA project (MaNGA: Mapping Nearby Galaxies at Apache Point Observatory) and the Very Large Telescope’s FLAMES: Fiber Large Array Multi Element Spectrograph. We isolate sources of fiber systematics and estimate the observed amplitude of persistent residuals as well as stochastic noise contributions resulting from changing fiber stresses. Comparing these levels against their impact on various sky subtraction schemes demonstrates that 0.1% precision sky subtraction with fiber instruments is possible. As a demonstration, we show that the MaNGA instrument can deliver 0.2% residuals on bright near-IR sky lines with nonlocal sky subtraction, if pseudo-slit limitations are addressed by allocating 50% of its fibers to sky. We further highlight recently published deep exposures that achieved a 1σ background level of 27.6 AB per square arc second, equivalent to a precision of 0.2% of the sky background continuum.

Peculiar motion of Solar system from the Hubble diagram of supernovae Ia and its implications for cosmology

ABSTRACTPeculiar motion of the Solar system, determined from the dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR), has given a velocity 370 km s−1 along RA = 168°, Dec. = −7°. Subsequent peculiar motion determinations from the number counts, sky brightness, or redshift dipoles observed in large samples of distant radio galaxies and quasars yielded peculiar velocities 2 to 10 times larger than CMBR, though in all cases the directions matched with the CMBR dipole. Here, we introduce a novel technique for determining the peculiar motion from the magnitude-redshift (mB–z) Hubble diagram of Type Ia Supernovae (SN Ia), one of the best standard candles available. We find a peculiar velocity 1.6 ± 0.5 × 103 km s−1, larger than the CMBR value roughly by a factor of four, along RA = 173° ± 12°, Dec. = 10° ± 9°, the direction being within $\stackrel{\lt }{_{\sim }}2\sigma$ of the CMBR dipole. Since a genuine solar motion would not depend upon the method or the data set employed, large discrepancies seen among various dipole amplitudes could imply that these dipoles, including the CMBR one, might not pertain to observer’s peculiar motion. However, a common direction for various dipoles might indicate a preferred direction in the Universe, implying an intrinsic anisotropy, in violation of the cosmological principle, a cornerstone of the modern cosmology.

Toward a Data-driven Model of the Sky from Low Earth Orbit as Observed by the Hubble Space Telescope

The sky observed by space telescopes in Low Earth Orbit (LEO) can be dominated by stray light from multiple sources including Earth, Sun, and Moon. This stray light presents a significant challenge to missions that aim to make a secure measurement of the extragalactic background light (EBL). In this work, we quantify the impact of stray light on sky observations made by the Hubble Space Telescope (HST) Advanced Camera for Surveys. By selecting on orbital parameters, we successfully isolate images with sky that contain minimal and high levels of earthshine. In addition, we find weather observations from CERES satellites correlate with the observed HST sky surface brightness indicating the value of incorporating such data to characterize the sky. Finally, we present a machine-learning model of the sky trained on the data used in this work to predict the total observed sky surface brightness. We demonstrate that our initial model is able to predict the total sky brightness under a range of conditions to within 3.9% of the true measured sky. Moreover, we find that the model matches the stray-light-free observations better than current physical zodiacal light models.

Majority of artificially lit Earth surface associated with the non-urban population

Key to understanding the negative impacts of artificial light at night (ALAN) on human health and the natural environment is its relationship with human density. ALAN has often primarily been considered an urban issue, however although over half of the population is urbanized, the 46 % that are not inhabit a dispersed array of smaller settlements. Here, we determine the global relationships between two dimensions of ALAN, namely direct emissions (radiance) and skyglow, and human density, and how these relationships vary across continents. We correct the Visible Infrared Imaging Radiometer Suite Day/Night Band (VIIRS DNB) product for albedo, skyglow, airglow, the aurora and permanent snow and ice to represent upward radiance overland at 1.61 ∗ 2.12 km resolution from artificial sources only. For skyglow we use the World Atlas of Artificial Sky Brightness. Globally (between 59°N and 55°S), direct emissions were detected over 26.5 % and skyglow over 46.9 % of land area. Over half of all cumulative direct emissions (54.9 %) were emitted at low levels by the non-urban population, whilst these populations experienced the negative impacts of over two-thirds of all cumulative skyglow (69.8 %). This emphasises the extent of ALAN outside of urban areas, and its similarity in this regard to a number of other forms of pollution. Although powerful sources of rural direct emissions (e.g., industry, recreation) are important contributors of light pollution, cumulatively they only contributed 10 % to total direct emissions. The relationship between each dimension of ALAN and population density varied across continents, driven by powerful rural emissions, non-urban populations and urban design. These relationships reflect the unique socio-economic and geographical make-up of each region and inform on where best to target light pollution mitigation strategies, not only in urban areas but also in rural ones.

TiEMPO: open-source time-dependent end-to-end model for simulating ground-based submillimeter astronomical observations

The next technological breakthrough in millimeter–submillimeter astronomy is three-dimensional imaging spectrometry with wide instantaneous spectral bandwidths and wide fields of view. The total optimization of the focal-plane instrument, the telescope, the observing strategy, and the signal-processing software must enable efficient removal of foreground emission from the Earth’s atmosphere, which is time-dependent and highly nonlinear in frequency. Here, we present Time-dependent End-to-end Model for Post-process Optimization (TiEMPO) of the DEep Spectroscopic HIgh-redshift MApper (DESHIMA) spectrometer. TiEMPO utilizes a dynamical model of the atmosphere and parameterized models of the astronomical source, the telescope, the instrument, and the detector. The output of TiEMPO is a time stream of sky brightness temperature and detected power, which can be analyzed by standard signal-processing software. We first compare TiEMPO simulations with an on-sky measurement by the wideband DESHIMA spectrometer, and find good agreement in the noise and sensitivity. We then use TiEMPO to simulate the detection of the line emission spectrum of a high-redshift galaxy using the DESHIMA 2.0 spectrometer in development. The TiEMPO model is open source. Its modular and parametrized design enables users to adapt it to optimize the end-to-end performance of spectroscopic and photometric instruments on existing and future telescopes.

The Universe is Brighter in the Direction of Our Motion: Galaxy Counts and Fluxes are Consistent with the CMB Dipole

An observer moving with respect to the cosmic rest frame should observe a concentration and brightening of galaxies in the direction of motion and a spreading and dimming in the opposite direction. The velocity inferred from this dipole should match that of the cosmic microwave background (CMB) temperature dipole if galaxies are on average at rest with respect to the CMB rest frame. However, recent studies have claimed a many-fold enhancement of galaxy counts and flux in the direction of the solar motion compared to the CMB expectation, calling into question the standard cosmology. Here we show that the sky distribution and brightness of extragalactic radio sources are consistent with the CMB dipole in direction and velocity. We use the first epoch of the Very Large Array Sky Survey combined with the Rapid Australian Square Kilometer Array Pathfinder Continuum Survey to estimate the dipole via several different methods, and all show similar results. Typical fits find a km s−1 velocity dipole with apex in Galactic coordinates from source counts and km s−1 toward from radio fluxes. These are consistent with the CMB-solar velocity, 370 km s−1 toward (ℓ, b) = (264, 48), and show that galaxies are on average at rest with respect to the rest frame of the early universe, as predicted by the canonical cosmology.

“I Did, I Did Taw a Puddy Tat!” Pumas in Urban Ecosystems of Latin America: A Review of the Mediatic Information

The concentration of people living in small areas has increased in the last decade, with more than half of the world's population living in cities. This is particularly true for Latin America, a region with no particular high contribution to the world total population, but hosts several large cities. The increase in urbanization causes several threats to wildlife that face the loss of their habitat and novel environmental pressures. As the number of wildlife entering cities seems to have increased in the last year, we characterize the temporal and geographical events of a widely distributed carnivore, the puma, Puma concolor. We performed an exhaustive search for media news regarding the sighting, capture, and/or killing of pumas within human settlement areas, and tried to relate them with potential explanatory variables. We found a total of 162 events in Latin America in a period of the last 10 years, particularly concentrated in the year 2020. Most records came from Brazil, followed by Argentina, Chile, and Mexico. Of the total, 41% were only sightings, 58% were captures, and a minor percentage were considered as mascotism. Almost the same number of records came from highly populated areas (cities) than from low populated areas (rural) but with important differences between countries. The countries with more records in urban areas (Brazil and Mexico) showed a larger surface occupied by cities. The countries with most records in rural areas (Argentina and Chile) present the opposite pattern of occupied surface. This might indicate that different percentages of areas dedicated to cities or urban spaces might explain the differences among countries. The most important variable related to puma events in the populated areas was sky brightness, while human density and cattle density explained minor parts. The “anthropause” due to the COVID-19 pandemic might explain the larger number of records from 2020, while the absence of high-quality habitats due to fragmentation and high cattle density, might force the pumas to enter populated areas searching for food. Minor values of night lights could be related to a facilitation of efficiency of foraging behavior. Although some bias might exist in the data, the results should be taken into account as general statements for all analyzed countries.

A revised simplified scattering model for the moonlit sky brightness profile based on photometry at SAAO

ABSTRACT This paper presents multifilter measurements of the night sky brightness at the South African Astronomical Observatory (SAAO) in Sutherland in the presence of a bright moon. The observations cover a wide range of sky directions, lunar phases, and lunar positions. A revised simplified scattering model is developed for estimating the sky brightness due to moonlight that more accurately reflects the atmospheric extinction of the lunar beam compared to models frequently applied in astronomical studies. Contributions to night sky brightness due to sources other than moonlight are quantified and subtracted from the total sky background radiation to determine the spectral intensity and angular distribution of scattered moonlight. The atmospheric scattering phase function is then derived by comparing the sky brightening to the strength of the incoming lunar beam, estimated using a novel approach. The phase function is shown to be an excellent match to the combined theoretical Rayleigh and Mie scattering functions, the latter with a Henyey–Greenstein form instead of the exponential angular relationship often used in previous studies. Where deviations between measured and model sky brightness are evident in some bands, these are explained by contributions from multiple scattering or airglow, and are quantified accordingly. The model constitutes an effective tool to predict sky brightness at SAAO in optical photometric bands, especially with a bright moon present. The methodology can also be readily be adapted for use at other astronomical sites. The paper furthermore presents UBV(RI)c and Strömgren photometry for 49 stars, most with no prior such data.

Photometric calibrations and characterization of the 4K$$\times $$4K CCD imager, the first-light axial port instrument for the 3.6m DOT

In the present work, recent characterization results of the 4K$\times$4K CCD Imager (a first light instrument of the 3.6m Devasthal Optical Telescope; DOT) and photometric calibrations are discussed, along with measurements of the extinction coefficients and sky brightness values at the location of the 3.6m DOT site based on the imaging data taken between 2016 and 2021. For the 4K$\times$4K CCD Imager, all given combinations of gains (1, 2, 3, 5, and 10 e$^-$/ADU) and readout noise values for the three readout speeds (100 kHz, 500 kHz, and 1 MHz) are verified using the sky flats and bias frames taken during early 2021; measured values resemble well with the theoretical ones. Using color-color and color-magnitude transformation equations, color coefficients ($\alpha$) and zero-points ($\beta$) are determined to constrain and examine their long-term consistencies and any possible evolution based on $UBVRI$ observations of several Landolt standard fields observed during 2016-2021. Our present analysis exhibits consistency among estimated $\alpha$ values within the 1$\sigma$ and does not show any noticeable trend with time. We also found that the photometric errors and limiting magnitudes computed using the CCD Imager data follow the simulated ones published earlier. The average extinction coefficients, their seasonal variations, and zenith night-sky brightness values for the moon-less nights for all ten Bessell and SDSS filters are also estimated and found comparable to those reported for other good astronomical sites.