Search Results (82)

Obtaining an antenna’s back-up structure (BUS) temperature field is an essential prerequisite for analyzing its thermal deformation. Thermodynamic simulation can obtain the structure’s thermal distribution, but it has low computational accuracy. There is a problem with cumbersome wiring and difficult maintenance of the temperature measurement system. This study developed an improved RIME-XGBoost model to realize the temperature prediction of the BUS of the Nanshan 26-m Radio Telescope (NSRT). The proposed model successfully predicts the NSRT’s BUS temperature distribution based solely on environmental sensing (ambient temperature, angle of solar radiation, antenna’s orientation, etc.). The relative prediction accuracy between the predicted and actual BUS temperature is 97.15%, and the predictive error is less than 0.897 K (root mean square error, RMSE). This research result provides an alternative method for the real-time reconstruction of the structure’s thermal distribution in large-aperture radio telescopes. Full article

In this paper, we investigate the thread oscillations in a quiescent prominence observed by New Vacuum Solar Telescope at the H$\alpha$ line center on 17 April 2024. Each individual thread is traced by the local maximum intensity on the time–distance maps. Although there are numerous threads in this prominence, 24 oscillating threads are identified at eight slits parallel to the solar surface. A sinusoidal function is used to fit them, and about 1.5 cycles of oscillations and a mean period of 27.7 min are detected. We find that all these 24 threads display the oscillation with almost a constant amplitude with an average value of about 0.92 Mm, with no damping or expansion during their lifetimes. Furthermore, we find the oscillations at different positions on a same thread almost have a similar period of 88.7 min in phase, which indicates that the thread oscillations could be triggered by a standing-type wave. Using the typical parameters in the prominence, the magnetic field strength (B) is estimated in the range of 4 G ≤ B ≤ 21 G, which is consistent with the previous results. Our findings would provide the clues for the thread oscillation mechanism in the prominence. Full article

Solar ground-layer adaptive optics (GLAO) is widely recognized as a key technology for achieving high-resolution, wide-field imaging in ground-based solar telescopes. However, the accuracy differences among various wavefront sensing methods in solar GLAO remain unclear. In this study, Monte Carlo simulations and indoor GLAO experiments were conducted to perform, for the first time, a comparative analysis of two representative wavefront sensing methods: multi-direction averaging (MD-A) and wide-field correlation (WF-C). The results demonstrate that WF-C consistently achieves higher detection accuracy than MD-A, although the differences between the two methods are small. With an increasing field of view (FoV), the detection accuracy of MD-A improves but remains lower than that of WF-C. In terms of correction performance, significant improvements in central FoV imaging were achieved using WF-C within narrow-to-moderate FoVs, whereas in wide and ultra-wide FoVs, MD-A produced more uniform image quality enhancements. Using the 1 m New Vacuum Solar Telescope (NVST) GLAO system as an example, MD-A is better suited to wide and future ultra-wide field imaging (over 80″), whereas WF-C is more appropriate for high-precision wavefront sensing within narrow to moderate fields (20″–60″). These findings provide both theoretical guidance and practical insights for the optimization of GLAO systems and wavefront sensing strategies in 1-meter-class wide-field solar telescopes. Full article

The ATLAS lidar on NASA’s Earth-orbiting ICESat-2 satellite has operated continuously since its launch in September 2018, with no sign of degradation. Compared to previous international single-beam spaceborne lidars, which operated at a few tens of Hz, the single-photon-sensitive, six-beam ATLAS pushbroom lidar provides 60,000 surface measurements per second and has accumulated almost 3 trillion surface measurements during its six years of operation. It also features a 0.5 m² telescope aperture and a single, 5 Watt, frequency-doubled Nd:YAG laser generating a 10 KHz train of 1.5-nanosecond pulses at a green wavelength of 532 nm. The current paper investigates how, with minor modifications to the ATLAS lidar, this capability might be extended to other planets within our solar system. Crucial to this capability is the need to minimize the solar background seen by the lidar while simultaneously providing, for long time intervals (multiple months), an uninterrupted, modestly powered, multimegabit per second interplanetary laser communications link to a terminal in Earth orbit. The proposed solution is a pair of Earth and planetary satellites in high, parallel, quasi-synchronized orbits perpendicular to their host planet’s orbital planes about the Sun. High orbits significantly reduce the time intervals over which the interplanetary communications link is blocked by their host planets. Initial establishment of the interplanetary communications link is simplified during two specific time intervals per orbit when the sunlit image of the two planets are not displaced from their actual positions (“zero point ahead angle”). In this instance, sunlit planetary images and the orbiting satellite laser beacon can be displayed on the same pixelated detector array, thereby accelerating the coalignment of the two communication terminals. Various tables in the text provide insight for each of the eight planets regarding the impact of solar distance on the worst-case Signal-to-Noise Ratio (SNR), the effect of satellite orbital height on the duration of the unblocked interplanetary communications link, and the resulting planetary surface continuity and resolution in both the along-track and cross-track directions. For planets beyond Saturn, the laser power and/or transmit/receive telescope apertures required to transmit multimegabit-per-second lidar data back to Earth are major challenges given current technology. Full article

The 1 June 2025 Forbush decrease in the terrestrial ground-level flux of cosmic ray secondaries was recorded by many cosmic ray systems. This was the deepest such decrease from the quiescent value of the flux, which has been observed over the past two decades. It resulted from a complex series of solar events, none of which on its own reached the most extreme level. The extreme depth of this decrease has enabled measurements of the flux reduction to be made, which would normally be severely limited by particle counting statistics. In particular, here we examine the decrease phenomenon over a primary cosmic ray energy range, which is rarely accessible due to the low flux of high energy cosmic rays. This work considers data mainly from a muon telescope system, which can respond to both unaccompanied muons and small cosmic ray air showers, providing data from GeV to mid-TeV energies, where the Forbush decrease ceases to be statistically observable. This paper examines the depth of the flux decrease, as a fraction below its quiescent value, over that primary energy range. The progressive development of internal time structure in the flux through the seven days of the phenomenon is also demonstrated. Full article

The Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS) has conducted continuous observations of solar vector magnetic fields for nearly four decades, and while the primary optical system remains unchanged, critical components—including filters, polarizers, and detectors—have undergone multiple upgrades and replacements. Maintaining data consistency is essential for reliable long-term studies of magnetic field evolution and solar activity, as well as current helicity. In this study, we systematically analyze background bias and noise levels in SMFT observations from 1988 to 2019. Our dataset comprises 12,281 vector magnetograms of 1484 active regions. To quantify background bias, we computed mean values of Stokes $Q/I$, $U/I$ and $V/I$ over each entire magnetogram. The background bias of Stokes $V/I$ is small for the whole dataset. The background biases of Stokes $Q/I$ and $U/I$ fluctuate around zero during 1988–2000. From 2001 to 2011, however, the fluctuations in the background bias of both $Q/I$ and $U/I$ become significantly larger, exhibiting mixed positive and negative values. Between 2012 and 2019, the background biases shift to predominantly positive values for both Stokes $Q/I$ and $U/I$ parameters. To address this issue, we propose a potential method for removing the background bias and further discuss its impact on the estimation of current helicity. For each magnetogram, we quantify measurement noise by calculating the standard deviation ($\sigma$) of the longitudinal ($B_{\mathrm{l}}$) and transverse ($B_{\mathrm{t}}$) magnetic field components within a quiet-Sun region. The noise levels for $B_l$ and $B_{\mathrm{t}}$ components were approximately 15 Gauss (G) and 87 G, respectively, during 1988–2011. Since 2012, these values decreased significantly to ∼6 G for $B_{\mathrm{l}}$ and ∼55 G for $B_{\mathrm{t}}$, likely due to the installation of a new filter. Full article

Galileo and the telescope revolutionized the concept of the Sun. The discovery of its rotation was possible due to the continuous observation of the sunspots. The faculae and the maculae with umbra and penumbra became accessible daily to new instruments, leaving the perfectly lucid disk to the realm of symbolism. Was this new view possible before the telescope? Technically, pinhole cameras can show the largest sunspots, as well as the naked eye under very particular conditions. However such observations were too scattered to produce any change in the established understanding of the Sun. Synoptic observations of the largest sunspots of the XXV solar cycle made with the naked eye, pinhole camera, and a telescope in camera obscura are presented and compared with the historical ones. Sunspots could have been discovered in Florence as early as 1475 with the pinhole meridian line of S. Maria del Fiore: the Spörer minimum (1460–1550) of the solar activity prevented it. Indications of white light flares and prominence observations appear in a drawing dated back to 1635, well before the first H-alpha inspections in the 19th century. Full article

We present a freeze-out approach for describing the formation of heavy elements in expanding nuclear matter. Applying concepts used in modeling heavy-ion collisions or ternary fission, we determine the abundances of heavy elements taking into account in-medium effects such as Pauli blocking and the Mott effect, which describes the dissolution of nuclei at high densities of nuclear matter. With this approach, we search for a universal initial distribution in a quasi-equilibrium state from which the coarse-grained pattern of the solar abundances of heavy elements freezes out and evolves by radioactive decay of the excited states. The universal initial state is characterized by the Lagrange parameters, which are related to temperature and chemical potentials of neutrons and protons. We show that such a state exists and determine a temperature of 5.266 MeV, a neutron chemical potential of 940.317 MeV and a proton chemical potential of 845.069 MeV, with a baryon number density of 0.013 fm⁻³ and a proton fraction of $0.13$. Heavy neutron-rich nuclei such as the hypothetical double-magic nucleus ³⁵⁸Sn appear in the initial distribution and contribute to the observed abundances after fission. We discuss astrophysical scenarios for the realization of this universal initial distribution for heavy-element nucleosynthesis, including supernova explosions, neutron star mergers and the inhomogeneous Big Bang. The latter scenario may be of interest in the light of early massive objects observed with the James Webb Space Telescope and opens new perspectives on the universality of the observed r-process patterns and the lack of observations of population III stars. Full article

We propose a novel telescope concept based on Earth’s gravitational lensing effect, optimized for the detection of distant dark matter sources, particularly axion-like particles (ALPs). When a unidirectional flux of dark matter passes through Earth at sufficiently high velocity, gravitational lensing can concentrate the flux at a distant focal region in space. Our method combines this lensing effect with stimulated backward reflection (SBR), arising from ALP decays that are induced by directing a coherent electromagnetic beam toward the focal point. The aim of this work is to numerically analyze the structure of the focal region and to develop a framework for estimating the sensitivity to ALP–photon coupling via this mechanism. Numerical calculations show that, assuming an average ALP velocity of 520 km/s—as suggested by the observed stellar stream S1—the focal region extends from $9\times {10}^9$ m to $1.4\times {10}^{10}$ m, with peak density near $9.6\times {10}^9$ m. For a conservative point-like ALP source located approximately 8 kpc from the solar system, based on the S1 stream, the estimated sensitivity in the eV mass range reaches $g/M=\mathcal{O}\left({10}^{-22}\right){\mathrm{GeV}}^{-1}$. This concept thus opens a path toward a general-purpose, space-based ALP observatory that could, in principle, detect more distant sources—well beyond $\mathcal{O}\left(10\right)\mathrm{kpc}$—provided that ALP–photon coupling is sufficiently strong, that is, $M\ll M_{\mathrm{Planck}}$. Full article

The precise monitoring of solar flares holds significant scientific value for space mission safety, communication security, and space environment forecasting. The H$\alpha$ line has long been utilized as a tool to extract information about the structure and dynamics of the solar chromosphere and is crucial for observing solar activities such as prominences and flares. However, ground-based H$\alpha$ observations are susceptible to cloud interference, which significantly reduces data reliability and complicates the effective separation of genuine flare signals from cloud modulation effects. To address this challenge, our study proposes a dual-band brightness ratio method tailored to the SMAT configuration, leveraging synchronous observation data from the Huairou SMAT at two wavelengths (photospheric 5324 Å and chromospheric 6562.8 Å). Observational data validation demonstrates that this method can effectively characterize true chromospheric brightness variations. In real observational data, the reconstructed brightness curve successfully recovered the brightness peak of an M1.5 class flare, with the peak position aligning well with the X-ray flux peak. This method enhances the accuracy of flare monitoring under cloudy conditions for SMAT, providing a promising pathway for high-reliability ground-based solar activity observations with this telescope. Full article

Water-ice occurs inside many minor bodies almost throughout the Solar System. To have an overview of the inventory of water-ice in asteroids, beside the general characteristics of their activity, examples are presented with details, including the Hilda zone and among the Trojans. There might be several extinct comets among the asteroids with only internal ice content, demonstrating the complex evolution of such bodies. To evaluate the formation of ice-hosting small objects, their migration and retention capacity by a surface covering dust layer are also overviewed to provide a complex picture of volatile occurrences. This review aims to support further work and search for sublimation-induced activity of asteroids by future missions and telescopic surveys. Based on the observed and hypothesized occurrence and characteristics of icy asteroids, future observation-related estimations were made regarding the low limiting magnitude future survey of LSST/Vera Rubin and also the infrared ice identification by the James Webb space telescope. According to these estimations, there is a high probability of mapping the distribution of ice in the asteroid belt over the next decade. Full article

Atmospheric optical turbulence intensity, quantified by the Fried parameter ($r_0$), serves as a critical metric for astronomical site testing and selection. The Solar Differential Image Motion Monitor (SDIMM), adapted from the methodology of the Differential Image Motion Monitor (DIMM), is a dedicated instrument for daytime $r_0$ measurements. Conventional SDIMM systems typically employ telescopes with apertures ≥30 cm and reconstruct wavefront segmentation at the exit pupil, resulting in bulky configurations that impede portability. To address the demands of multi-site surveys, we developed a low-cost, portable SDIMM system that directly adopts the DIMM optical path without backend wavefront reconstruction, instead deriving $r_0$ through image processing algorithms. Integrated with a 20 cm aperture telescope, the system achieves a total weight of <20 kg, significantly enhancing field portability. This paper details the instrument’s architecture, measurement principles, and comparative tests with a traditional SDIMM, demonstrating strong consistency between the two systems. Field measurements conducted at the Ali Observatory (elevation: 5050 m) from 16 August to 10 December 2024 yielded the site’s first continuous daytime $r_0$ dataset, with values ranging from 1.5 cm to 12 cm and a mean of 4.09 cm. The compact SDIMM provides a cost-effective and easily deployable solution for comparative daytime $r_0$ assessments across multiple candidate astronomical sites. Full article

The S-band (i.e., 2–4 GHz) is essential in multiple fields of radio astronomy, ranging from pulsar and solar studies to investigations of the early universe. The Italian 64 m fully steerable Sardinia Radio Telescope (SRT) is a system designed to operate in a wide frequency band ranging from 300 MHz to 116 GHz. Recently, the Astronomical Observatory of Cagliari (OAC) has been developing a new cryogenic seven-beam S-band radio receiver. This paper describes the design, fabrication and electromagnetic characterization of the feed horn for this new receiver. It has been designed to observe the sky in the 3–4.5 GHz frequency range and it will be composed of seven feed horns arranged in a regular hexagonal layout with a central element. The feed horns are optimized for placement in the primary focus and consequently illuminate the 64 m primary mirror of the SRT. The electromagnetic characterization of the single feed horn is crucial to verify the receiver’s performance; for this reason, a single feed horn has been manufactured to compare the measured reflection coefficient and the radiated far-field diagram with the results of the electromagnetic simulations, performed using the CST^® Suite Studio 2024 and Ansys HFSS^® Electromagnetics Suite 2021 R1 (To make the S-parameters and the radiation diagram measurement procedure feasible, the single feed horn has been connected to two adapters: a circular-to-rectangular waveguide adapter and a coax-to-rectangular waveguide adapter. The results of the measurements performed in the anechoic chamber are in very good agreement with the simulated results. Additionally, the feed horn phase center position is evaluated, merging the measurements and simulations results for an optimal installation on the primary focus of the SRT. Full article

The mid-infrared band is the last major observational window for the ground-based large solar telescopes in the 21st century. Achieving ultra-narrowband filter imaging is a fundamental challenge that all solar telescopes encounter as they progress towards the mid-infrared spectrum. The guided-mode resonance filtering (GMRF) technology provides a promising solution to this critical issue. This paper describes in detail the fundamental principles and calculation procedure of guided-mode resonance filtering. Building upon this foundation, a preliminary design and simulation of a mid-infrared guided-mode resonance filter are carried out. The results show that when the thickness of the sub-wavelength grating is an even multiple of the half-wavelength, it is feasible to attain ultra-narrowband filtering with a bandwidth below 0.03 nm by increasing the grating thickness and decreasing the grating fill factor. Nevertheless, the high sensitivity of the resonant wavelength to the angle of incidence still stands as a formidable obstacle that demands further investigation and resolution. Full article

Retrolensing is a gravitational lensing effect in which light emitted by a background source is deflected by a black hole and redirected toward the observer after undergoing nearly complete loops around the black hole. In this context, we explore the possibility of seeing objects of the solar system in past eras through telescope observations by using black holes as a gravitational mirror. We consider the motion of the light around Reissner–Nordström space–time and discuss the properties of the trajectories of boomerang photons. It was shown that, depending on the angle of emission and the position of the source, the photons could return to the emission point. Afterward, we explore the possibility of considering the returning photons in retrolensing geometry where the observer is between the source and the lens in which two classes of black holes are explored: The supermassive Sgr A* black hole at the galactic center and a nearby stellar black hole. For the first time in the literature, we propose the study of the returning photons of planets instead of stars in retrolensing geometry. Full article