Night Sky Research Articles

Atmospheric extinction coefficients and night sky brightness at ITB-Undana remote telescope site

Abstract A remote telescope system has been established at Universitas Nusa Cendana, Kupang. Bosscha Observatory, Institut Teknologi Bandung (ITB), and the Physics Study Program at Universitas Nusa Cendana (Undana) collaborated to develop the system. The ITB-Undana Telescope system has a QSI 616 CCD camera and BV RI Bessel filter attached to a 20-cm (f/10) Schmidt-Cassegrain reflector. Several research and public outreach activities have been conducted using the ITB-Undana remote telescope throughout 2023. When establishing a new astronomical observation site, it is imperative to conduct sky characterization and quality assessment. This process involves measuring night sky brightness and atmospheric extinction coefficients. In May 2023, we observed photometric standard stars using the absolute photometry technique with BV RI Bessel filters. We also utilized the Sky Quality Meter (SQM) to measure night sky brightness over three nights from May 24th to May 26th, 2023, to compare the sky brightness values obtained through the absolute photometry method. Our initial measurement shows a first-order extinction coefficient value ranging from k b ′ = 0.269 to 0.520, k v ′ = 0.216 to 0.297, k r ′ = 0.019 to 0.206, and k i ′ = 0.127 to 0.163, for B, V, R, and I filter, respectively. Application of extinction coefficient value in the sky field gives a mean sky brightness value in V bandpass, V sky = 19.431 ± 0.022, with color index (B − V )sky = 0.492 ± 0.039. These night sky brightness values are suitable for measurements using the SQM.

DIY Photometer Performance Test in Determining Morning Twilight

Abstract Do-It-Yourself (DIY) Sky Quality Meter (SQM) known as D.I.Y – CJ’01 Photometer has been successfully built and tested. Using SQM as a calibrated portable photometer is a hot topic of astronomical research regarding night sky brightness measurement. The output data obtained by the photometer is in unit of magnitude per square arc second (mag/sq arcsecond ∼ mpsas) value with a maximum value of 21.7 mpsas as a quantization of the representation of a very dark sky with the presence of natural airglow. The sky brightness then gradually increases with values up to 16.7 mpsas, which is when the sky is brighter due to the presence of artificial airglow from outdoor artificial lighting such as in big cities. This research aims to determine the D.I.Y – CJ’01 Photometer performance in measuring the sky brightness of morning twilight. The research method used in this work is an experiment with data collection from D.I.Y - CJ’01 Photometer and SQM Unihedron gathered from two locations in Cimahi and Bandung. Data processing shows that the D.I.Y - CJ’01 Photometer mimics the performance of SQM Unihedron, with the the smallest difference for the value of the solar depression angle in morning twilight measurements is 0.06%.

An accurate and realistic polarization model for night-sky brightness

Abstract Most measurements of the diffuse light of the night sky to date consider only the intensity of the light field, and current models can successfully reproduce these measurements. However, this approach is incomplete as it overlooks the polarization state of the light. Few measurements (and no successful models) of night-sky polarimetry appear in the literature. We present a new model of night-sky polarization that successfully reproduces observations in a heterogeneous environment and for a real distribution of finite-sized light sources over the intermediate region surrounding the observer. The model compares favourably with field measurements made in Slovakia in May 2021. The results described herein help advance understanding the angular distributions of artificial light at night from ground sources and the relative contributions of sources to the overall brightness of the night sky.

Let there be Skyglow—light pollution from a large outdoor music festival (Lollapalooza Berlin 2016)

Live music is often linked to elaborate light shows, particularly at large outdoor music festivals. However, artificial light at night is one form of environmental pollution, light pollution, and because outdoor festivals emit a substantial amount of artificial light into the environment, they are a potential source of light pollution. So far, no studies that quantified the impact of such festivals on urban light pollution and skyglow exist. Here, the light pollution produced by a major rock festival (Lollapalooza Berlin 2016 with 70,000 visitors per day in an urban park) was investigated with ground-based radiometry and night-time light data. A small night-sky radiometer installed near the main stages and a calibrated digital camera from a nearby observation spot inside of the park were used to quantify changes in night sky brightness and direct light emissions within the park. The impact of the music festival on the urban skyglow was indeed measurable. Zenith luminance increased locally by up to a factor of 8 and illuminance increased by about 50% at the observation spot within the park. The radiance detected by night-time satellite was also increased during the festival. This is the first time, that light pollution from such a major rock music event was quantified.

Autumn's Sky

This is an image of the night sky in the northern hemisphere’s autumn. If you look carefully, you can see the Milky Way, the constellation Cassiopeia, and even the Milky Way’s biggest neighbor, the Andromeda Galaxy.

Tiger beetles produce anti-bat ultrasound and are probable Batesian moth mimics.

Echolocating bats and their eared insect prey are in an acoustic evolutionary war. Moths produce anti-bat sounds that startle bat predators, signal noxiousness, mimic unpalatable models and jam bat sonar. Tiger beetles (Cicindelidae) also purportedly produce ultrasound in response to bat attacks. Here we tested 19 tiger beetle species from seven genera and showed that they produce anti-bat signals to playback of authentic bat echolocation. The dominant frequency of beetle sounds substantially overlaps the sonar calls of sympatric bats. As tiger beetles are known to produce defensive chemicals such as benzaldehyde and hydrogen cyanide, we hypothesized that tiger beetle sounds are acoustically advertising their unpalatability. We presented captive big brown bats (Eptesicus fuscus) with seven different tiger beetle species and found that 90 out of 94 beetles were completely consumed, indicating that these tiger beetle species are not aposematically signalling. Instead, we show that the primary temporal and spectral characteristics of beetle warning sounds overlap with sympatric unpalatable tiger moth (Arctinae) sounds and that tiger beetles are probably Batesian mimics of noxious moth models. We predict that many insect taxa produce anti-bat sounds and that the acoustic mimicry rings of the night sky are hyperdiverse.

The Night Sky Brightness Measurement using OZT-ALTS Telescope based on Sky Quality Meter

The Night Sky Brightness Measurement using OZT-ALTS Telescope based on Sky Quality Meter

Direct comparison of SiPM and PMT sensor performances in a large-size imaging air Cherenkov telescope

The peak photon detection efficiency (PDE) of silicon photomultipliers (SiPMs) can be as good or better than the PDE of photomultiplier tubes (PMTs). There are experiments where the signal is measured in the presence of a strong, steady background light emission. In these, one needs to accurately evaluate the signal-to-noise ratio. Imaging Atmospheric Cherenkov Telescopes (IACT) observe in the presence of strong noise induced by the light of the night sky. It is certainly interesting to investigate the SiPM performance under operational conditions of IACTs and to compare it with that of the PMTs.For that purpose, we built a SiPM-based detector module, which was installed in one of the imaging cameras of the two Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes in 2015. The experience gained from that module was used to design the second generation of modules of improved performance. Two such modules were installed in 2017.MAGIC is a system of two IACTs located on the Canary Island of La Palma. The mechanical structure of the MAGIC imaging cameras offers the possibility to install up to 6 additional detector modules of 7 pixels each into the open vertices of the hexagonal-shaped camera. This allows us to directly, without making any assumption, compare the performance of the PMT-based modules with that of the SiPM-based prototype modules, where SiPMs from three different manufacturers are used.

The impact of ambient temperature on the spectral characteristics of LED sources in the context of astronomical observations of the night sky

The Spectral Power Distribution (SPD) of artificial light sources is a crucial factor in determining the extent of night sky degradation due to light pollution. External temperature affects the properties of LED lamps, including their SPD. In this study, we investigated the impact of ambient temperatures ranging from -25°C to 25°C on the spectral characteristics of 14 LED sources used in outdoor lighting. The obtained SPDs were then used to calculate the Scotopic Sky Luminance Ratio index, enabling the assessment of changes in night sky degradation. Full Text: PDF References K. Baran, A. Różowicz, H. Wachta, S. Różowicz, "Modeling of Selected Lighting Parameters of LED Panel", Energies, 13(14), 3583 (2020). CrossRef P. Tabaka, "Influence of Replacement of Sodium Lamps in Park Luminaires with LED Sources of Different Closest Color Temperature on the Effect of Light Pollution and Energy Efficiency", Energies, 14(19), 6383 (2021). CrossRef P. Tabaka, P. Rozga, "Influence of a Light Source Installed in a Luminaire of Opal Sphere Type on the Effect of Light Pollution", Energies, 13(2), 306 (2020). CrossRef P. Tabaka (ed.), "Sztuczne światło nocą między zagrożeniem a rozwojem", Lodz University of Technology Press (2022), CrossRef D. Sanders, E. Frago, R. Kehoe, Ch. Patterson, K. J. Gaston, "A meta-analysis of biological impacts of artificial light at night", Nature Ecology & Evolution, 5: 74-81 (2021). CrossRef F. Falchi, P. et al.,, "The new world atlas of artificial night sky brightness", Science Advances, 2, 6 (2016). CrossRef R. F. Green, Ch. B. Luginbuhl, R. J. Wainscoat, D. Duriscoe, "The growing threat of light pollution to ground-based observatories", Astron. Astrophys. Rev., 30, 1 (2022). CrossRef C.C.M. Kyba, "Is light pollution getting better or worse?", Nature Astronomy, 2: 267-269 (2018), CrossRef CIE 2019 "CIE Spectral luminous efficiency for scotopic vision" CrossRef P. Tabaka, S. Kołomański, "Influence of replacing discharge lamps with LED sources in outdoor lighting installations on astronomical observations", Bull. Pol. Acad. Sci. Tech. Sci., 71, 6 (2023). CrossRef M. Deląg, S. Różowicz, A. Różowicz, H. Wachta, "Impact of Ambient Temperature on the Colour Temperature of Low-pressure Mercury Discharge Lamps", Energetyka-Elektryka-Zakłócenia, 12(3) (2021). CrossRef M. Oleksy, J. Kraśniewski, W. Janke, "Wpływ temperatury na charakterystyki optyczne i elektryczne diod LED mocy", Przegląd Elektrotechniczny, 90(9), 83 (2014). CrossRef H. Horvath et al., "Optical characteristics of the aerosol in Spain and Austria and its effect on radiative forcing", J. Geophys. Res., 107, D19 (2002). CrossRef Raport IMGW-PIB DirectLink

The night sky as a heritage of humanity and Astrotourism as a tourist potential in the rural regions of Rosana/SP

The present study aimed to present a review of the literature regarding the interconnection between the quality of the night sky and the growing interest in astrotourism. As a basis for data collection, studies of secondary documentary nature were used. It is observed that the subject grows in interest on the part of scholars considering the possibilities of application of the astrotourism activity, due to the distinctive elements of offer in the field of tourism, in addition to appearing as a playful element in the perception of tourists. The study is relevant considering the still small amount of studies in Brazil on the subject and the possibility of incorporating this type of service in the national tourist trade, in addition to being able to appear as a distinctive element of the offer in rural areas, like others countries.

Assessing the Influence of Urban Lights on Night Sky Brightness with a Smartphone

The darkness of the sky is a critical parameter for assessing the suitability of an astronomical site. Among various sources of light pollution, urban lights pose the most significant threat to ground-based optical astronomical and planetary observations. Quantitatively assessing the impact of urban lights with varying scales and fluxes is indispensable for selecting an ideal optical observation site. In order to quantitatively assess the changes in Night Sky Brightness (NSB) relative to the distance from urban areas and to establish a foundation for safeguarding the light environment at the newly developed Lenghu astronomical site on the Tibetan Plateau, we employed both a Sky Quality Meter and a pre-calibrated smartphone. These instruments were used to measure the NSB in the vicinity of two cities, Da Qaidam and Delingha, which vary in size and radiant flux, on the Tibetan Plateau. The findings indicate that the NSB around both cities decreases significantly as the distance from the city center increases, although the rate of decrease varies between the two locations. This decline can be effectively modeled using an exponential decay function. Notably, the influence of city lights on NSB becomes negligible at distances exceeding 30 km from Da Qaidam, while for Delingha, this distance extends to 50 km due to its larger city size and higher total radiant flux. The methodologies and results presented in this paper offer valuable insights for the selection of astronomical observation sites and the development of light pollution management policies.

Fusion of a priori information and energy distribution for the centroiding method of the star sensor

The star sensor is the most accurate measurement instrument in the spacecraft attitude measurement system, and the accurate centroid of the star point is the basis for ensuring the performance of the star sensor. Currently, the centroid of the gray method is the most widely used centroid extraction method in practice. Systematic errors caused by the centroid of the gray method and random noise in the detector imaging process are the main factors contributing to the deviation of the star centroiding coordinates. Considering the relationship between the point spread function and the pixel gray value, this paper proposes a centroiding method to reduce the star point centroiding error by fusing a priori information and energy distribution. The star charts are first preprocessed using a curvature filter and Gaussian blur to reduce the random noise. Then the complexity of the point spread function is considered, and the pixel gray values are corrected based on a priori information and gray value fuzzy processing. Finally, the symmetry of the one-dimensional energy distribution is used to quickly determine the sub-pixel deviation to get the star centroid coordinates. Through simulation and physical simulation experiments, the method was verified to be effective, and the extraction accuracy met the requirements of high-precision star sensors. The night sky observation test results demonstrate that the method in this paper can improve the measurement accuracy of the star sensors.

Measurement of the zodiacal light absolute intensity through Fraunhofer line spectroscopy of the night sky with the Hale telescope

Abstract Measuring the absolute brightness of the zodiacal light (ZL), which is the sunlight scattered by interplanetary dust particles, is important not only for understanding the physical properties of the dust but also for constraining the extragalactic background light (EBL) by subtracting the ZL foreground. We describe the results of high-resolution spectroscopic observations of the night sky in the wavelength range of 300–900 nm with the double spectrograph on the Hale telescope to determine the absolute brightness of the ZL continuum spectra from the Fraunhofer absorption line intensities. The observed fields are part of the fields observed by the Spitzer Space Telescope for the EBL study. Assuming that the spectral shape of the zodiacal light is identical to the solar spectrum in a narrow region around the Fraunhofer lines, we decomposed the observed sky brightness into multiple emission components by amplitude parameter fitting with spectral templates of the airglow, ZL, diffuse Galactic light, integrated starlight, and other isotropic components including EBL. As a result, the ZL component with the Ca ii λλ 393.3, 396.8 nm Fraunhofer lines around 400 nm is clearly separated from the others in all fields with uncertainties around 20%, mainly due to the template errors and the time variability of the airglow. The observed ZL brightness in most of the observed fields is consistent with the modeled ZL brightness calculated by combining the most conventional ZL model at 1250 nm based on the Diffuse Infrared Background Experiment and the observational ZL template spectrum based on the Hubble Space Telescope. However, the ecliptic plane observation is considerably fainter than the ZL model, and this discrepancy is discussed in terms of the optical properties of the interplanetary dust accreted in the ecliptic plane.

Exploring Community Self-efficacy to Light Pollution Mitigation in A Tourism Destination

ABSTRACT Light pollution is an emergent environmental concern, it disrupts the natural patterns of wildlife, contributes to the increase in carbon dioxide in the atmosphere, disrupts human sleep, and obscures the stars in the night sky. However, rural and urban communities often overlook this factor, since it is not seen as a problem, and even if the destination has taken measures to mitigate light pollution, it is still challenging to maintain optimal levels. This study applied a questionnaire (N = 366) to examine the community involvement in light pollution mitigation in a Portuguese rural tourism destination in 2023. Results demonstrated that tourism is not a sufficient incentive for participants to take individual measures to mitigate light pollution (β = 0.075, p = 0.243). However, they consider that integrating tourism with light pollution mitigation at the local community level could enhance the tourist experience (β = 0.427, p = 0.000). Tourism destinations should promote environmental education about the effects of light pollution.

Satellite Hyperspectral Nighttime Light Observation and Identification with DESIS

The satellite imagery of nighttime lights (NTLs) has been studied to understand human activities, economic development, and more recently, the ecological impact of brighter night skies. The Visible Infrared Imaging Radiometer Suite (VIIRS) Day–Night Band (DNB) offers perhaps the most advanced nighttime imaging capabilities to date, but its large pixel size and single band capture large-scale changes in NTL while missing granular but important details, such as lighting type and brightness. To better understand individual NTL sources in a region, the spectra of nighttime lights captured by the DLR Earth Sensing Imaging Spectrometer (DESIS) were extracted and compared against near-coincident VIIRS DNB imagery. The analysis shows that DESIS’s finer spatial and spectral resolutions can detect individual NTL locations and types beyond what is possible with the DNB. Extracted night light spectra, validated against ground truth measurements, demonstrate DESIS’s ability to accurately detect and identify narrow-band atomic emission lines that characterize the spectra of high-intensity discharge (HID) light sources and the broader spectral features associated with different light-emitting diode (LED) lights. These results suggest the possible application of using hyperspectral data from moderate-resolution sensors to identify lamp construction details, such as illumination source type and light quality in low-light contexts. NTL data from DESIS and other hyperspectral sensors may improve the scientific understanding of light pollution, lighting quality, and energy efficiency by identifying, evaluating, and mapping individual and small groups of light sources.

The ArgusSpec Prototype: Autonomous Spectroscopic Follow-up of Flares Detected by Large Array Telescopes

ArgusSpec is a prototype autonomous spectroscopic follow-up instrument designed to characterize flares detected by the Argus Pathfinder telescope array by taking short exposure (30 s) broadband spectra (370–750 nm) at low resolutions (R ∼ 150 at 500 nm). The instrument is built from consumer off-the-shelf astronomical equipment, assembled inside a shipping container, and deployed alongside the Argus Pathfinder at a dark sky observing site in Western North Carolina. In this paper, we describe the hardware design, system electronics, custom control software suite, automated target acquisition procedure, and data reduction pipeline. We present initial on-sky test data used to evaluate system performance and show a series of spectra taken of a small flare from AD Leonis. The $35k prototype ArgusSpec was designed, built, and deployed in under a year, largely from existing parts, and has been operating on-sky since 2023 March. With current hardware and software, the system is capable of receiving an observation, slewing, performing autonomous slit acquisition, and beginning data acquisition within an average of 32 s. With Argus Pathfinder’s 1 s cadence survey reporting alerts of rising sources within 2 s of onset, ArgusSpec can reach new targets well within a minute of the start of the event. As built, ArgusSpec can observe targets down to a 20σ limiting magnitude of m V ≈ 13 at 30 s cadence with an optical resolution of R ∼ 150 (at 500 nm). With automated rapid acquisition demonstrated, later hardware upgrades will be based on a clean-sheet optical design, solving many issues in the current system, significantly improving the limiting magnitude, and potentially enabling deep spectroscopy by the coaddition of data from an array of ArgusSpec systems. The primary science driver behind ArgusSpec is the characterization of the blackbody evolution of flares from nearby M-dwarfs. Large flares emitted by these stars could have significant impacts on the potential habitability of any orbiting exoplanets, but our current understanding of these events is in large part built on observations from a handful of active stars. ArgusSpec will characterize large numbers of flares from across the night sky, building a spectroscopic library of the most extreme events from a wide variety of stellar masses and ages.

Visitor outcomes from dark sky tourism: a case study of the Jasper Dark Sky Festival

ABSTRACT Dark sky tourism is a growing, but under-studied sector of ecotourism. While some research has examined the economic impacts, regional sustainability, and management of dark sky tourism, researchers know little about tourist experiences and outcomes. This study seeks to determine visitor outcomes (satisfaction, learning, attitudes, and behavior changes) among participants at the Jasper Dark Sky Festival in Alberta, Canada. Visitors were middle-aged, balanced between genders, traveled an average of 430 km, and were primarily urban-based. Most were first-time visitors, were present 2 or more days, and attended over 5 festival events. Respondents reported high satisfaction levels, due to the low cost and diversity of events, and welcoming nature of the community, presenters, and volunteers. Respondents reported many areas of learning, particularly about the night sky and night animals. Respondents had very positive attitudes about protecting dark skies, but only 42% planned to change any behaviors to protect dark skies. Study results will help festival organizers design dark sky tourism events to optimize visitor outcomes. In particular, festival organizers can address some barriers to behavioral change, such as stressing the value of dark skies and providing information about how to reduce light pollution.

Moonless night sky increases Isistius species (cookiecutter shark) and live human contact.

The nocturnal feeding behavior and zoogeographical habitat of cookiecutter sharks Isistius brasiliensis and Isistius plutodus (Isistius spp.) greatly reduces interaction of this species with live humans. Attacks on live humans are exceedingly rare with 7 cases reported worldwide, 6 of them in Hawai'i, and 5 of these occuring among channel swimmers. Published research suggests that periods of bright moonlight may increase Isistius spp. contact with live humans and does not otherwise identify significant trends or risk factors. Yet 5 of the 6 Isistius spp. bites on live humans in Hawai'ian waters occurred with the moon set and after nautical twilight end and before nautical twilight start. From 1961-2023 in Hawai'i, 129 successful solo channel crosses and 5 Isistius spp. related injuries in the habitat of cookiecutter sharks were analyzed across two groups: one where both the moon and sun were set (dark group) and one where the moon and/or sun was in the sky (light group). There was a significant difference for swimmers bitten by Isistius spp. in the dark 4 (12%) versus light groups 1 (1%), p = 0.012, RR 12.6 (95% confidence interval: 1.5-108.9). Swim start time and year was also significant (Pearson correlation 0.566, p <0.001). Swimmer gender and use of shark deterrent devices and artificial illumination were not significant. The growing popularity of channel swimming in Hawai'i and swim start times have contributed to an increasing likelihood of live human and Isistius spp. contact and a moonless night sky is a significant risk factor for this interaction.

Polarisation vision in the dark: green-sensitive photoreceptors in the nocturnal ball-rolling dung beetle Escarabaeus satyrus.

Many insects utilise the polarisation pattern of the sky to adjust their travelling directions. The extraction of directional information from this sky-wide cue is mediated by specialised photoreceptors located in the dorsal rim area (DRA). While this part of the eye is known to be sensitive to the ultraviolet, blue or green component of skylight, the latter has only been observed in insects active in dim light. To address the functional significance of green polarisation sensitivity, we define the spectral and morphological adaptations of the DRA in a nocturnal ball-rolling dung beetle-the only family of insects demonstrated to orient to the dim polarisation pattern in the night sky. Intracellular recordings revealed polarisation-sensitive green photoreceptors in the DRA of Escarabaeus satyrus. Behavioural experiments verified the navigational relevance of this finding. To quantify the adaptive value of green sensitivity for celestial orientation at night, we also obtained the polarisation properties of the night sky in the natural habitat of the beetle. Calculations of relative photon catch revealed that under a moonlit sky the green-sensitive DRA photoreceptors can be expected to catch an order of magnitude more photons compared with the UV-sensitive photoreceptors in the main retina. The green-sensitive photoreceptors - which also show a range of morphological adaptations for enhanced sensitivity - provide E. satyrus with a highly sensitive system for the extraction of directional information from the night sky.

Embracing firefly flash pattern variability with data-driven species classification

Many nocturnally active fireflies use precisely timed bioluminescent patterns to identify mates, making them especially vulnerable to light pollution. As urbanization continues to brighten the night sky, firefly populations are under constant stress, and close to half of the species are now threatened. Ensuring the survival of firefly biodiversity depends on a large-scale conservation effort to monitor and protect thousands of populations. While species can be identified by their flash patterns, current methods require expert measurement and manual classification and are infeasible given the number and geographic distribution of fireflies. Here we present the application of a recurrent neural network (RNN) for accurate automated firefly flash pattern classification. Using recordings from commodity cameras, we can extract flash trajectories of individuals within a swarm and classify their species with an accuracy of approximately seventy percent. In addition to its potential in population monitoring, automated classification provides the means to study firefly behavior at the population level. We employ the classifier to measure and characterize the variability within and between swarms, unlocking a new dimension of their behavior. Our method is open source, and deployment in community science applications could revolutionize our ability to monitor and understand firefly populations.