Clear Nights Research Articles

The Multi-band Survey Telescope at Zhongshan Station, Antarctica

ABSTRACTThe Antarctic Plateau is considered to be the best ground-based astronomical site on Earth. Compared with other middle latitude observatories, the telescopes located in Antarctica have unique advantages in seeing a large fraction of clear nights, continuous observing window in the polar night, and so on. China has operated several generations of telescopes in Antarctica, but has not yet achieved multicolour simultaneous observation with tracking. Multi-band Survey Telescope (MST) is the first multicolour simultaneous survey telescope in Antarctica. It adopts a Newtonian telescope structure which is different from other Antarctic telescopes and is matched with a new alignment scheme suitable for the harsh environment of Antarctica. In addition, MST is equipped with a defrosting indium tin oxide (ITO) window and a high-precision equatorial mount. This paper introduces the optical design, mechanical structure, and analysis of the actual operation of MST in Antarctica. Since March 2022, MST has been carrying out the observation normally in Zhongshan Station, and the operation of MST has provided a new experience for the follow-up design and installation of Antarctic telescopes. We plan to further optimize the design and manufacture of MST, and develop it as a standard model of small-aperture Antarctic telescopes for space debris observations and time-domain surveys.

Passive Daytime Radiative Cooling of Silica Aerogels.

Silica aerogels are one of the most widely used aerogels, exhibiting excellent thermal insulation performance and ultralow density. However, owing to their plenitude of Si-O-Si bonds, they possess high infrared emissivity in the range of 8-13 µm and are potentially robust passive radiative cooling (PRC) materials. In this study, the PRC behavior of traditional silica aerogels prepared from methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) in outdoor environments was investigated. The silica aerogels possessed low thermal conductivity of 0.035 W/m·K and showed excellent thermal insulation performance in room environments. However, sub-ambient cooling of 12 °C was observed on a clear night and sub-ambient cooling of up to 7.5 °C was achieved in the daytime, which indicated that in these cases the silica aerogel became a robust cooling material rather than a thermal insulator owing to its high IR emissivity of 0.932 and high solar reflectance of 0.924. In summary, this study shows the PRC performance of silica aerogels, and the findings guide the utilization of silica aerogels by considering their application environments for achieving optimal thermal management behavior.

Prehistoric Astronomical Observatories and Paleoclimatic Records in Bulgaria Estimate Astroclimate during 4000–4500 BCE: A Critical Assessment

Prehistoric astronomical observatories include a specific type of rock-cut monuments from the Mountainous Thrace in Bulgaria, with a specific shape and orientation in space, which are part of the characteristic representatives of the archeoastronomical sites on the Balkan Peninsula from the period of 4000–4500 BCE. Earlier societies focused on the triad “astronomical instrument”—celestial objects—trained observers. When choosing sites for the construction of oriented stone complexes for astronomical observations, prehistoric people were interested in the number of clear days and nights within the tropical year, which is connected with the paleoclimate of the region and to the astroclimate, which determines the possibility of observing heavenly bodies. Here we examine 13 prehistoric astronomical observatories using the methods of archaeoastronomy in order to determine the period of their operation. Since the existence of a large number of such objects is indirect evidence of a good astroclimate, we make an assessment of the paleoclimate in the relevant era in the Bulgarian lands in order to find out if it was suitable for astronomical observations. The estimations are made according to the geological data and solar insolation luminescence proxy records of the evolution of cave speleothems from Duhlata cave in the village of Bosnek, Pernik municipality, which is still the only available experimental record of past solar insolation in Europe covering the last 20,000 years. The number of clear days and nights are estimated, and a critical assessment of the possibility of successful observations of the Sun during equinoxes and solstices is made using the methods of “horizon” astronomy and meridional culminations. It is also shown that the climate at the end of the Ice Age was cooler than today. About 11,700 years ago (11,700 radiocarbon years before 1950 CE or 11,700 BP), the climate began to warm, and forest vegetation developed on the territory liberated from the glaciers. During the Upper Atlantic (6–8 thousand years BCE), the average annual temperature on the Balkan Peninsula and in particular in Bulgaria was about 2–2.5 °C higher than it is today. This climate allows some very good astroclimatic conditions for observations of the Sun near the horizon and increases the accuracy of the observational data in determining the time of occurrence in its extreme positions on the horizon. We show that changes in climate (and astroclimate accordingly) influence the type of prehistoric astronomical observatories.

Effects of Concrete Block Flooring on Greenhouse Microclimate and Floor Surface Heat Balance

Greenhouse floor management is essential for effectively utilizing solar energy in horticultural production. Covering soil floors with concrete is one method of greenhouse floor management. This paper assesses the effects of this method on greenhouse microclimate and floor surface heat balance by comparing two adjacent single-span greenhouses, namely, an “interlocking concrete block floor” greenhouse (ICFG) and an “uncovered soil floor” greenhouse (SFG). During days with high solar radiation in 2019 winter, the maximum air temperature was 10.0°C lower, and the average vapor pressure was 0.5 kPa lower in the ICFG than in the SFG. On clear nights, the average air temperature was 1.6°C higher in the ICFG than in the SFG. The concrete floor had a higher albedo than the soil floor. This contributed to the lower daytime temperatures in the ICFG. The lower heat absorption by the concrete during the day was more than compensated for by a larger total transmission of heat from the ground to the greenhouse air at night due to the greater thermal conductivity of concrete. These results indicate that replacing soil floors with concrete floors could help farmers avoid temperature extremes and high daytime humidity without requiring external energy derived from fossil fuels or other sources.

A simulation-based study to evaluate the cooling potential of nocturnal radiative cooling systems for residential buildings in Egypt

During the first years of the last decade, Egypt used to face recurrent electricity cut-offs in summer. In the past few years, the electricity tariff dramatically increased. Radiative cooling to the clear night sky is a renewable energy source that represents a relative solution. The dry desert climate promotes nocturnal radiative cooling applications. This study investigates the potential of nocturnal radiative cooling systems (RCSs) to reduce the energy consumption of the residential building sector in Egypt. The system technology proposed in this work is based on uncovered solar thermal collectors integrated into the building hydronic system. By implementing different control strategies, the same system could be used for both cooling and heating applications. The goal of this paper is to analyze the performance of RCSs in residential buildings in Egypt. The dynamic simulation program TRNSYS was used to simulate the thermal behavior of the system. The relevant issues of Egypt as a case-study are firstly overviewed. Then the paper introduces the work done to develop a building model that represents a typical residential apartment in Egypt. Typical occupancy profiles were developed to define the internal thermal gains. The adopted control strategy to optimize the system operation is presented as well. To fully understand and hence evaluate the operation of the proposed RCS, four simulation cases were considered: 1. a reference case (fully passive), 2. the stand-alone operation of the RCS, 3. ideal heating & cooling operation (fully-active), and 4. the hybrid-operation (when the active cooling system is supported by the proposed RCS). The analysis considered the main three distinct climates in Egypt, represented by the cities of Alexandria, Cairo and Asyut. The hotter and drier weather conditions resulted in a higher cooling potential and larger temperature differences. The simulated cooling power in Asyut was 28.4 W/m² for a 70 m² absorber field. For a smaller field area of 10 m², the cooling power reached 109 W/m² but with humble temperature differences. To meet the rigorous thermal comfort conditions, the proposed sensible RCS cannot fully replace conventional air-conditioning units, especially in humid areas like Alexandria. When working in a hybrid system, a 10% reduction in the active cooling energy demand could be achieved in Asyut to keep the cooling set-point at 24 °C. This percentage reduction was nearly doubled when the thermal comfort set-point was increased by two degrees (26 °C). In a sensitivity analysis, external shading devices as a passive measure as well as the implementation of the Egyptian code for buildings (ECP306/1–2005) were also investigated. The analysis of this study raised other relevant aspects to discuss, e.g. system-sizing, environmental effects, limitations and recommendations.

‘허구’와 ‘비허구’의 경계

Yan Lianke’s Blind Date, Clear Night is a novel with a strong transformation into a kind of curtain call that conveys a different direction of raising questions compared to the previously published work. What method was more important to him than what he wrote. If the article is intended to restore humanity by exposing its wounds as a huge media outlet, such as criticism of revolutionary ideology that overwhelms mankind, false consciousness of intellectuals, and suffering and anger of the Chinese people, it is a confession and reflection. In this “Quick Seeking Co-sleeping”, he once again implemented this “wild” to the end. The whole book tells a fictional story under non-fiction in a completely new way, and reality and fiction are constantly blended, blurring the relationship between the two.
 Yan Lianke’s can feel three major changes in his 20-year career as a writer. First of all, his writing was very realistic in the early days, but later on, it became more complicated by combining irrationality with various elements such as modernism, postmodernism, magic realism, black humor, and dreams. Second, writing for literature and freedom, even if it is no longer published, and third, thinking and efforts as “intellectuals” as much as possible, not just as a novelist, are important factors in the three changes.
 Yan Lianke’s novels are known in literary circles as “surrealism”. Speaking of realistic literary creation, Yan Lianke sighed: “Realism is not only about writing about people, it would be too shallow to limit realism to the description of social ecology.” Realist literature is not just about people and human nature, but about the survival dilemma of the whole person. If you want to write about the dilemma deeply, you have to learn to observe, and sometimes it is more important to observe other people’s lives than to observe your own life.”

The set‐up and evaluation of fine‐scale data assimilation for the urban climate of Amsterdam

AbstractOngoing urbanization highlights the need for a better understanding and high resolution modelling of the urban climate. In this study, we combine rural observations by WMO surface stations, weather radar data and urban crowd‐sourced observations with very fine‐scale modelling efforts for Amsterdam, The Netherlands. As a model, we use the Weather Research and Forecasting (WRF) mesoscale model with 3D variational data assimilation at a 100‐m resolution in the innermost model domain. In order to enable the assimilation of observations within the urban canopy, we develop a scheme to reduce urban temperature biases by adjusting urban fabric temperatures. The scheme is tested against independent urban observations for the summer month of July 2014 and specifically for a hot period and an extreme precipitation event. We find data assimilation reduces biases in temperature and wind speed. Within the city, the most significant improvement is the reduction of negative temperature biases during clear nights, which implies a better prediction of the Urban Heat Island (UHI). Concerning precipitation, the fractional skill score improves incrementally when additional observations are assimilated, and the largest impact is seen from the assimilation of weather radar observations.

Controlling the artificial radiance of the night sky: The Añora urban laboratory

We provide radiometric evidence of the relevance of nearby light sources on the artificial brightness of the night sky. To obtain the required data we developed a method based on the use of power-regulated urban lighting systems, which also provides relevant information on the propagation of light pollution at short distances from the sources. A controlled experiment was carried out in the Andalusian municipality of Añora (1526 inhab.) in which the radiant power of its regulated public outdoor lighting system was modified in a predefined way during the central part of the night while continuously recording the zenith sky brightness in the TESS-W photometric band from two separate locations inside the town. We determined that the power-regulated streetlight sources contribute a 60–62% to the total zenith sky brightness at these observing locations in clear and moonless nights when operated at their maximum power rating, being the remaining sky radiance due to constant local sources and sources from neighboring towns. These results, in combination with georeferenced information on the sources' location and properties, impose some constraints on the functional form of the effective point-spread functions (PSF) of the zenith sky brightness at short distances from the sources. For the conditions of our experiment we have found that the expected exponents of power-law PSFs are close to -1.

Seven years of quasi-continuous LIDAR data

We have analyzed seven years of quasi-continuous LIDAR data taken during those nights when the MAGIC telescopes were operating. Characterization of the nocturnal ground layer is possible through an absolute calibration of the LIDAR during clear nights and yields zenith and azimuth-angle dependent aerosol extinction scale heights for clear nights. We derive aerosol transmission statistics for light emitted from various altitudes throughout the year and separated by seasons. We find further seasonal dependencies of cloud base and top altitudes. The Cumbre Vieja volcano dust plume observation is shown to highlight the possibilities and limitations of our method.

Investigations on Concentric Gravity Wave Sources Over the Brazilian Equatorial Region

AbstractObservations of concentric gravity waves (CGWs) in the OH airglow emission over the Brazilian equatorial region are presented. An all‐sky imager installed at São João do Cariri [7.4°S, 36.5°W] was used to acquire near‐infrared OH images. Using over 19 years of observational data from 2000 to 2019, more than 1,052 clear sky nights of airglow data were acquired with a total of 25 observed CGW cases. Three CGW events were selected for this study. These waves had small‐scale characteristics and well‐defined concentric structures. The selected CGW events showed horizontal wavelengths λH ∼ 31.9, 42.5, and 30.9 km, horizontal phase speeds cH ∼ 49.2, 57.6, and 74.1 m/s, and periods τ ∼ 10.8, 12.3, and 7.0 min, respectively. The CGW structures were well defined, with coherent wave patterns expanding concentrically from the source point, with the observed events having semi‐circle or arc‐like and semi‐elliptical shapes. We found the occurrence of the CGWs to coincide with the seasons of intense tropospheric convective activity and low background winds. This suggests little or no wave breaking, critical level absorption, and filtering or reflection, thereby allowing the CGWs to propagate up to the mesosphere and lower thermosphere region. Using backward ray tracing, we also found the positions and times where and when the ray paths reached the tropopause. The tropopause positions and times of two of the CGW events coincide with active convective systems with cold cloud top temperatures. However, the tropopause position of one of the 3 CGW events did not coincide with any active convective system, suggesting that this CGW was most likely generated in‐situ.

Dual-Layered Titanium Oxide-Acrylic Film on Carbon Black for Passive Radiative Cooling below Ambient Temperature under Direct Solar Irradiance

Cooling is an energy-intensive process; and with the effects of global warming, space conditioning poses more load on the scarce and costly energy available for consumption in facilities. Thus, the use of a passive sub-ambient diurnal radiative cooler, which is an effective natural space cooling technology, can help reduce the total energy demand for buildings. A diurnal passive radiative cooler of 40 × 40 cm, has been designed, fabricated, and experimentally investigated. The cooler comprises a photonic solar reflector and thermal emitter made of titanium dioxide embedded in an epoxy resin that reflects 96% of insolation and emits strongly in the 8-13 µm atmospheric window. Design calculations were made under Owerri climatic conditions. The results obtained showed that when the cooler was exposed to direct insolation well above 950 W/m2 , it achieved a drop in temperature of 1-2 °C below ambient between 6 am and 9 am. As the solar radiation increased, the temperature of the cooler increased until it reached 41 °C, which was above the ambient air temperature (30 °C). The cooler temperature decreased as the solar radiation decreased, dropping below the ambient temperature from 5:45 pm, by 3 °C during the remaining hours of the investigation. The photonic radiative cooler has an estimated cooling power of 56.8 W/m2 under a clear night sky and achieved sub-ambient cooling during the early and late hours of the day under low solar radiation. Therefore, passive cooling through the photonic approach offers prospects for energy efficiency. Further works may have the prospects of achieving improved passive sub-ambient daytime cooling.

A Novel All-Weather Method to Determine Deflection of the Vertical by Combining 3D Laser Tracking Free-Fall and Multi-GNSS Baselines

The bright stars in the clear night sky with weak background lights should be observed in the traditional deflection of the vertical (DOV) measurement so that the DOV cannot be observed under all-weather conditions, which limits its wide applications. An all-weather DOV measurement method combining three-dimensional (3D) laser tracking free-fall and multi-GNSS baselines is proposed in this paper. In a vacuum environment, the 3D laser tracking technique is used to continuously track and observe the motion of free-fall with high frequency and precision for obtaining 3D coordinate series. The plumb line vector equation is established to solve the gravity direction vector in the coordinate system of the laser tracker at the measuring point using least squares fitting coordinate series. Multi-GNSS observations are solved for obtaining the precise geodetic cartesian coordinates of the measuring point and GNSS baseline information. A direction transformation method based on the baseline information proposed in this paper is used to convert the gravitational direction vector in the laser tracker coordinate system into the geodetic cartesian coordinate system. The geodetic cartesian coordinates of the measuring point are used to calculate the ellipsoid normal vector, and the angle between this and the gravity direction vector in the geodetic cartesian coordinate system is estimated to obtain the astrogeodetic DOV. The DOV is projected to the meridian and prime vertical planes to obtain the meridian and prime vertical components of the DOV, respectively. The astronomical latitude and longitude of the measuring point are calculated from these two components. The simulation experiments were carried out using the proposed method, and it was found that the theoretical precision of the DOV measured by the method could reach 0.2″, which could realise all-weather observation.

Using ground-based thermal imagery to estimate debris thickness over glacial ice: fieldwork considerations to improve the effectiveness

AbstractDebris-covered glaciers are an important component of the mountain cryosphere and influence the hydrological contribution of glacierized basins to downstream rivers. This study examines the potential to make estimates of debris thickness, a critical variable to calculate the sub-debris melt, using ground-based thermal infrared radiometry (TIR) images. Over four days in August 2019, a ground-based, time-lapse TIR digital imaging radiometer recorded sequential thermal imagery of a debris-covered region of Peyto Glacier, Canadian Rockies, in conjunction with 44 manual excavations of debris thickness ranging from 10 to 110 cm, and concurrent meteorological observations. Inferring the correlation between measured debris thickness and TIR surface temperature as a base, the effectiveness of linear and exponential regression models for debris thickness estimation from surface temperature was explored. Optimal model performance (R2 of 0.7, RMSE of 10.3 cm) was obtained with a linear model applied to measurements taken on clear nights just before sunrise, but strong model performances were also obtained under complete cloud cover during daytime or nighttime with an exponential model. This work presents insights into the use of surface temperature and TIR observations to estimate debris thickness and gain knowledge of the state of debris-covered glacial ice and its potential hydrological contribution.

Experimental Study of Hybrid Flat-Plate Solar Collector/Nocturnal Radiator for Water Heating and Cooling in Owerri, Nigeria

The quest for new, alternative energy sources and technologies have risen due to myriads of crises associated with fossil fuel dominated energy mix in Nigeria, in terms of supply and its adverse effect on the environment.
 Experimental study of hybrid flat-plate solar collector/nocturnal radiator for water heating and cooling in Owerri, Nigeria, is presented. The experimental rig consists of a single flat surface (absorber plate) made of a mild steel plate, film-coated with an acrylic resin which made the surface spectrally selective. Underneath, were arrays of copper tube risers. A sample test on acrylic resin’s coating, on a metallic substrate showed that it has high clear spectral absorptivity (low emissivity) in the solar radiation band (0.2-0.3µm) as well as low absorptivity (high emissivity) in the atmospheric window band (3-8µm). A water reservoir 2m above was connected to the system inlet header to supply water. Experimental data were harvested for days/nights through a read-out basic language programmed data logger. The experimentation were conducted under the metrological condition of Federal Polytechnic Nekede Owerri (5.49oN, 7.02oE), South-East Nigeria. The results obtained under solar heating phase showed a peak water temperature of 60⁰C at a plate temperature of about 80⁰C and a heat collection efficiency of 31%. The peak insolation was about 900W/m2 and the ambient temperature was between 27⁰C and 32⁰C throughout the diurnal phase. Also, under the nocturnal radiation phase, a cooling power of 41w/m2 was achieved during cooling on clear night and about 20w/m2 on a cloudy night. Water temperature in the range of 19⁰C to 20⁰C was recorded at temperature depression of about 5⁰C. The night sky temperature of the location was obtained in the range 10⁰C to 16⁰C for the period under study. The result shows that the system can provide substantial energy savings when incorporated into building structure, to providing hot and cold water for domestic/process use, space heating and cooling applications.

Asynchronous object-oriented approach to the automation of the 0.8-meter George Mason University campus telescope in Python

We present a unique implementation of Python coding in an asynchronous object-oriented programming (OOP) framework to fully automate the process of collecting data with the George Mason University (GMU) Observatory's 0.8-meter telescope. The goal of this project is to perform automated follow-up observations for the Transiting Exoplanet Survey Satellite (TESS) mission, while still allowing for human control, monitoring, and adjustments. Prior to our implementation, the facility was computer-controlled by a human observer through a combination of webcams, TheSkyX, ASCOM Dome, MaxIm DL, and a weather station. We have automated slews and dome movements, CCD exposures, saving FITS images and metadata, initial focusing, guiding on the target, using the ambient temperature to adjust the focus as the telescope cools through the rest of the night, taking calibration images (darks and flats), and monitoring local weather data. The automated weather monitor periodically checks various weather data from multiple sources to automate the decision to close the observatory during adverse conditions. We have organized the OOP code structure in such a way that each hardware device or important higher-level process is categorized as its own object class or "module" with associated attributes and methods, with inherited common methods across modules for code reusability. To allow actions to be performed simultaneously across different modules, we implemented a multithreaded approach where each module is given its own CPU thread on which to operate concurrently with all other threads. After the initial few modules (camera, telescope, dome, data I/O) were developed, further development of the code was carried out in tandem with testing on sky on clear nights. The code, in its current state, has been tested and used for observations on 171 nights, with more planned usage and feature additions.

Characterizing the aerosol atmosphere above the Observatorio del Roque de los Muchachos by analysing seven years of data taken with an GaAsP HPD-readout, absolutely calibrated elastic LIDAR

ABSTRACT We present a new elastic LIDAR concept, based on a bi-axially mounted Nd:YAG laser and a telescope with HPD readout, combined with fast FADC signal digitization and offline pulse analysis. The LIDAR return signals have been extensively quality checked and absolutely calibrated. We analyse seven years of quasi-continuous LIDAR data taken during those nights when the MAGIC telescopes were operating. Characterization of the nocturnal ground layer yields zenith and azimuth angle dependent aerosol extinction scaleheights for clear nights. We derive aerosol transmission statistics for light emitted from various altitudes throughout the year and separated by seasons. We find further seasonal dependencies of cloud base and top altitudes, but none for the LIDAR ratios of clouds. Finally, the night sky background light is characterized using the LIDAR photon backgrounds.

Nighttime Atmospheric Scattering Phase Function Derived From the Scattered Light of a Laser Beam

AbstractContinuous monitoring of the atmospheric scattering phase function is difficult to perform since most observational techniques are limited to daylight hours. Among known aerosol optical properties, only atmospheric optical depth is measured routinely during clear nights at a few ground stations. In this paper we develop theoretical and experimental techniques to retrieve the scattering phase function from radiometry of a laser beam whose light is scattered in the lower nocturnal atmosphere. The field experiment we conducted in a night environment demonstrates the capability of the method to determine in real‐world settings. We show that extracting the scattering phase function from radiance data is realizable over a wide range of angles, which makes possible the use of an analytical extrapolation to approximate across the full range of scattering angles.

Propagating characteristics of mesospheric gravity waves observed by an OI 557.7 nm airglow all-sky camera at Mt. Bohyun (36.2° N, 128.9° E)

Abstract. We analysed all-sky camera images observed at Mt. Bohyun observatory (36.2∘ N, 128.9∘ E) for the period 2017–2019. The image data were acquired with a narrowband filter centred at 557.7 nm for the OI airglow emission at ∼ 96 km altitude. A total of 150 wave events were identified in the images of 144 clear nights. The interquartile ranges of wavelength, phase speed and periods of the identified waves are 20.5–35.5 km, 27.4–45.0 m s−1 and 10.8–13.7 min with the median values of 27.8 km, 36.3 m s−1 and 11.7 min, respectively. The summer and spring bias of propagation directions of north-eastward and northward, respectively, can be interpreted as the effect of filtering by the prevailing winds in the lower atmosphere. In winter the subdominant north-westward waves may be observed due to a nullified filtering effect by slow northward background wind or secondary waves generated in the upper atmosphere. Intrinsic phase speeds and periods of the waves were also derived by using the wind data simultaneously observed by a nearly co-located meteor radar. The nature of vertical propagation was evaluated in each season. The majority of observed waves are found to be freely propagating and thus can be attributed to wave sources in the lower or upper atmosphere.

TIME AND HUMAN FRAGILITY IN THE LANDSCAPE SIMILES OF THE ILIAD

AbstractThis article explores the propensity of Iliadic landscape similes to encourage reflections on human fragility. Landscape in the similes is usually interpreted as a medium which conveys a consistent symbolic value (for example storms as the hostility of nature); however, landscape is often a more flexible medium. By offering close readings of three Iliadic similes (winter torrents at 4.452–6, snowfall at 12.279–89 and clear night at 8.555–9), this article argues that landscape allowed the poet to frame the main narrative in various ways, both helping the listener to imagine described events and interrupting the listener's immersion in the main narrative. While many have analysed how similes offer analogies to the main narrative, the ways in which the same simile can also disrupt and reframe the narrative are less understood. This article observes that shifts in narrative space and time played a key role in changing the perspective of the listener. Taking a broadly phenomenological approach, it proposes that embodied descriptions of space, which recreate the experience of the moving body in landscape, invite the listener to consider the temporal scale of the natural world. By looking at how landscape in select similes shifts the listener's spatial and temporal experience, this article argues that landscape contributes to the wider Iliadic theme of human fragility. In particular, it identifies the potential for landscape similes to minimize the scale of human experience, question the possibility of human agency, and reveal the limitations of human perspectives and knowledge.

Nighttime electric power generation at a density of 50 mW/m2 via radiative cooling of a photovoltaic cell

A large fraction of the world's population lacks access to the electric grid. Standard photovoltaic (PV) cells can provide a renewable off-grid source of electricity but only produce power from daytime solar irradiance and do not produce power at night. While there have been several theoretical proposals and experimental demonstrations of energy harvesting from the radiative cooling of a PV cell at night, the achieved power density is very low. Here, we construct a device, which incorporates a thermoelectric generator that harvests electricity from the temperature difference between the PV cell and the ambient surrounding. We achieve 50 mW/m2 nighttime power generation with a clear night sky, with an open-circuit voltage of 100 mV, which is orders of magnitude higher as compared with previous demonstrations. During the daytime, the thermoelectric generator also provides additional power on top of the electric power generated directly from the PV cells. Our system can be used as a continuous renewable power source for both day- and nighttime in off-grid locations.