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The paper presents new detailed radar maps and polarimetric data covering the southern polar region of the near side of the Moon measuring 400 × 800 km with a spatial resolution of about 75 m. The data were obtained using the 64-meter antenna (TNA-1500) of the Satellite Communications Center Bear Lakes of the Special Design Bureau of the Moscow Power Engineering Institute and the 13.2-meter radio telescope (RT-13) of the Svetloe Observatory of the Institute of Applied Astronomy, Russian Academy of Sciences, at a wavelength of 4.2 cm. At this wavelength, radar signals penetrate the lunar regolith to depths of up to 1 m and are sensitive to surface and suspended rocks larger than 1 cm. The maps show 39% of the area of permanently shadowed regions not observable by optical Earth-based instruments, which may hide water ice deposits. Analysis of radar maps did not reveal any relationship between the polarization properties of the surface in these regions and the presence of solar illumination. The data obtained as a result of this work can be used to study the surface and subsurface regolith features of the lunar south polar region, including searching for ice deposits in permanently shadowed regions, as well as for planning future lunar missions. [ABSTRACT FROM AUTHOR]

Context. Time series photometry offers astronomers the tools to study time-dependent astrophysical phenomena, from stellar activity to fast radio bursts and exoplanet transits. Transit events, in particular, are focussed primarily on planetary transits and eclipsing binaries with eclipse geometries that can be parameterised with a few variables. However, more complex light curves caused by the substructure within the transiting object would require a customised analysis code. Aims. We present Beyond Circular Eclipsers (BeyonCE), which reduces the parameter space encompassed by the transit of circumsec-ondary disc (CSD) systems with azimuthally symmetric, non-uniform optical-depth profiles. By rejecting disc geometries that are not able to reproduce the measured gradients within their light curves, we can constrain the size and orientation of discs with a complex sub-structure. Methods. We mapped out all the possible geometries of a disc and calculated the gradients for rings crossing the star. We then rejected those configurations where the measured gradient of the light curve is greater than the theoretical gradient from the given disc orientation. Results. We present the fitting code BeyonCE and demonstrate its effectiveness in considerably reducing the parameter space of discs that contain an azimuthally symmetric structure. We used the code to analyse the light curves seen towards J1407 and PDS 110, attributed to CSD transits. [ABSTRACT FROM AUTHOR]

Refractive and diffractive solar sails have been cited to yield benefits in both performance and utility over reflective sails, but their range of viable flight regimes and future applications have not been fully explored. In this paper, a flight model is developed to test and compare these transmissive sail designs under realistic conditions. Raw performance is translated into tangible flight characteristics within a range of flight regimes, such as rate change of orbital energy and minimum operational altitude, and used to make comparison with reflective sails and contemporary thrusters. Additionally, the sensitivity of these flight characteristics to certain orbital parameters is explored when operating under either a locally optimal or simplified Sun-pointing steering law. The developed flight model focuses on solar radiation pressure, atmospheric drag and the effects of eclipse and orbital precession; locally optimal steering laws are numerically generated for every flight regime using a ray tracing-derived performance sensitivity profile. Relative to an idealised reflective sail, the sensitivity of transmissive sail performance is found to be lower for altitude, but higher for orbital inclination. High performance transmissive sail designs are found to outperform idealised reflective ones in every flight regime nonetheless. Meanwhile, only certain lower performance designs demonstrate this trait; others retain advantage only within high inclination, low altitude orbits. 36 m 2 transmissive sails performing an orbit-raising manoeuvre from low Earth orbit are shown to generate transit times comparable to mid-range electric thrusters. In light of these findings, potential applications for transmissive sails are discussed, as well as several practical considerations and potential limitations. • Solar sail performance and operational flexibility improved by transmissive membranes. • Non-meta transmissive sails find advantage at low altitude and/or high inclination. • Transmissive metasails find advantage in every flight regime. • Transmissive sails may fulfil contemporary thruster roles in low Earth orbit. • Transmissive sails may provide feasible space debris mitigation strategy. [ABSTRACT FROM AUTHOR]

Ptolemy reports three dated lunar eclipses observed by Hipparchus, and also refers to two more, without identifying them, which Hipparchus compared with two earlier counterparts (apparently, observed in Mesopotamia) to assess the validity of the Babylonian period relations of the lunar motion. Also, in Pliny the Elder's Historia naturalis, we are told that a horizontal lunar eclipse (selenelion) at sunrise and moonset was reported (observed?) by Hipparchus. Reviewing a paper by G.J. Toomer in 1980, it is shown that the pairs of the eclipses were, almost certainly, the ones occurring on "31 January 486 b.c. and 27 January 141 b.c." and "19 November 502 b.c. and 14 November 157 b.c."; and if Hipparchus observed from St. Stephen's Hill in Rhodes, the most probable candidate for the selenelion at moonset was the lunar eclipse of 7 February 142 b.c., although he also had the chance to observe any of the four others, occurring on 3 July 150 b.c., 10 April 145 b.c., 26 November 139 b.c., and 15 November 138 b.c., on a sufficiently elevated mountain on the island. [ABSTRACT FROM AUTHOR]

Two solar eclipse events in 2023 appeared to produce considerable enhancements in the thermospheric column density ratio of monatomic oxygen to molecular nitrogen (ΣO/N2) as measured by TIMED GUVI. We quantify potential sources for eclipse‐induced ΣO/N2 changes and find that the observed enhancements arise from the ionospheric O+ radiative recombination contribution to the OI 135.6 nm emission from which ΣO/N2 is derived. Variations in the solar Extreme Ultra Violet (EUV) and X‐ray spectrum, due to the difference between the disk spectrum and the coronal spectrum, are also considered but shown to have negligible contributions to the ΣO/N2 enhancements. After accounting for the radiative recombination contribution, we constrain the real thermospheric compositional change to the uncertainty level of the measurements of 5%–10%. These results are valuable for the interpretation of eclipse‐induced ΣO/N2 changes that will further first‐principle model comparisons and lead to a better understanding of the response of the thermosphere to localized variations in solar EUV and X‐ray forcing. Plain Language Summary: The Thermosphere Ionosphere Mesosphere Energetics and Dynamics' Global Ultraviolet Imager provides an estimate of the column ratio of monatomic oxygen (O) to molecular nitrogen (N2) in the upper atmosphere (ΣO/N2) as a data product under normal, sunlit conditions. Eclipses are special conditions. In this paper, we model the measured ultraviolet emissions from O and N2 that go into the retrieval algorithm to understand why this increase in the radiance ratio occurs within the totality of the eclipse. There are two components to the O emission, the glow created by electrons (photoelectrons) that result from the ionization of the upper atmosphere and the glow created by recombination of ionospheric O+ ions. We find that the photoelectron source decreases significantly during the eclipse, but near the magnetic equator, the ionospheric recombination emission does not, which causes the retrieval algorithm to overestimate the ΣO/N2 column density ratio during eclipses. The observations and models are consistent with this explanation. Key Points: The apparent thermospheric ΣO/N2 enhancements (10%–30%) for two eclipse events are found to be predominantly of ionospheric originVariations in the solar spectrum due to wavelength‐dependent attenuation are found to have a negligible impact on ΣO/N2 during the eclipseThe true eclipsed‐induced thermosphere compositional changes are determined to be within 5%–10% of the pre‐eclipse values [ABSTRACT FROM AUTHOR]

More than 50,000 spectators descended on the city of Carbondale, Illinois, to witness the much-anticipated total solar eclipse of 2024. Carbondale was in the path of totality for this astronomical [...]

Direct, simultaneous imaging of the full Moon rising asthe Sunwas setting proves that both objects can be seen concurrently. The onset of a total lunar eclipse provided the opportunity to capture this event near its most extreme possible separation. [ABSTRACT FROM AUTHOR]

It is expected that the extreme mass accretion rate onto strongly magnetized neutron stars results in the appearance of accretion columns above the stellar surface. For a distant observer, rotation of a star results in periodic variations of X-ray flux. Because the mass accretion rate fluctuates around the average value, the pulse profiles are not stable and demonstrate fluctuations as well. In the case of bright X-ray pulsars, however, pulse fluctuations are not solely attributed to variations in the mass accretion rate. They are also influenced by the variable height of the columns, which is dependent on the mass accretion rate. This study delves into the process of pulse profile formation in bright X-ray pulsars, taking into account stochastic fluctuations in the mass accretion rate, the corresponding variations in accretion column geometry, and gravitational bending. Our analysis reveals that potential eclipses of accretion columns by a neutron star during their spin period should manifest specific features in pulse profile variability. Applying a novel pulse profile analysis technique, we successfully detect these features in the bright X-ray transient V 0332+53 at luminosities |$\gtrsim 2\times 10^{38}\, {\rm erg\ \rm s^{-1}}$|⁠. This detection serves as compelling evidence for the eclipse of an accretion column by a neutron star. Detection of the eclipse places constraints on the relation between neutron star mass, radius, and accretion column height. Specifically, we can establish an upper limit on the accretion column height, which is crucial for refining theoretical models of extreme accretion. [ABSTRACT FROM AUTHOR]

Datable graphical records of total solar eclipses allow us to assess contemporaneous variability of Earth's rotation speed, solar coronal structure, and solar-wind conditions. Such graphical records were studied back to the early 18th century. Here, we examine Matthew Paris' medieval manuscript, an eyewitness account of a total solar eclipse just after local sunrise on 1230 May 14, to analyse his drawings for this eclipse. We philologically identify his observational site as St. Albans and compute local eclipse visibility. To locate St. Albans in the totality path, our analysis requires an accumulative error in time due to the variation in the Earth's rate of rotation, Δ T , in the range 394 s < Δ T  < 764 s (loose scenario), slightly revising the latest published Δ T spline curve. The eclipsed Sun sould have been visible after local sunrise if we set the Δ T margins to 394 s < Δ T  < 659 s (strict scenario), which requires a further slight modification of the latest Δ T spline curve. Matthew Paris' drawing of the total solar eclipse showed streamer-like structures similar to solar-minimum-type coronal streamers, consistent with the local tilt of the apparent solar equator. This is morphologically consistent with the minimum-type solar coronal streamers predicted from the open solar flux reconstructed from the 14C data set. This record potentially demonstrates a similarity in solar cycles between the 'Medieval Grand Maximum' and modern solar cycles. Collectively, historical eclipse records could be used as spot references for Earth's rotation speed, solar coronal dynamics, and background solar dynamo activity on a millennial time-scale. [ABSTRACT FROM AUTHOR]

This study comprehensively evaluated the signal-in-space range errors (SISREs) and investigated the systematic error characteristics for GPS and BDS broadcast ephemeris. The analysis reveals that on March 28, 2021, the satellite antenna model used by GPS ground operation centre to generate GPS II series navigation ephemeris changed from the manufacturer model to the International GNSS Service (IGS) model. This transition is carefully considered in our GPS SISRE evaluation. Experimental statistics indicate that the SISRE for GPS IIR, IIF, and III satellites is approximately 0.50, 0.46, and 0.34 m, respectively, with a value of 0.44 m for the overall constellation. With enhancements in inter-satellite links, BDS-3 GEO, IGSO, and MEO satellites exhibit SISRE of 1.20, 0.62, and 0.46 m, respectively, representing improvements of 14.3, 27.5 and 48.8 % over their BDS-2 counterparts. The ephemeris performance of BDS-3 MEOs is comparable to GPS. However, the BDS orbit quality significantly degrades over a 3-day period following manoeuvre operations and during eclipse seasons. Furthermore, the systematic error characteristics of broadcast ephemeris are analysed based on satellite laser ranging (SLR) checks and Helmert transformation. The SLR residuals of nearly all of the BDS-2/3 satellites tracked by the International Laser Ranging Service vary linearly with the Sun elongation angle. Moreover, the Z -geocentre component of the GPS/BDS orbit-realises frame exhibits obvious annual periodicity. These indicate that the GPS/BDS broadcast orbit models need further improvement. Compared with GPS, the BDS broadcast orbit-realised frame can better maintain the X - and Y -geocentric components but presents significant systematic scale bias and rotation errors. These errors for BDS are attributable to the inconsistency in the radial disturbance models between broadcast and Multi-GNSS Experiment precise orbits as well as prediction errors of the Earth rotation parameter used. The overall SLR residual mean for BDS-3 CAST and SECM MEOs are approximately 7.8 and −4.7 cm, respectively, with a standard deviation of approximately 9.9 cm, 3–4 times better than that of the BDS-2 satellites. The SLR residual dispersion of BDS-3 MEO C43 and C44 satellites is significantly larger than that of other BDS-3 MEOs, likely because of the inaccurate official coordinates of laser retroreflector arrays. [ABSTRACT FROM AUTHOR]

RW Aurigae is a young stellar system containing a classical T Tauri star as the primary component. It shows deep, irregular dimmings, first detected in 2010. At the University Observatory Jena, we carried out optical follow‐up observations. We performed multiband (BVRI) photometry of the system with the Cassegrain‐Teleskop‐Kamera II and the Schmidt‐Teleskop‐Kamera between September 2016 and April 2019, as well as spectroscopy, using the Fibre Linked ÉCHelle Astronomical Spectrograph between September 2016 and April 2018. We present the apparent photometry of RW Aur, which is consistent with and complementary to photometric data from the American Association of Variable Star Observers. The V‐band magnitude of RW Aur changed by up to three magnitudes during the timespan of our monitoring campaign. For the observing epochs 2016/2017 and 2017/2018 we report a decreasing brightness, while in the epoch 2018/2019 the system remained in a relatively constant bright state. In the color‐magnitude diagram, we see that RW Aur lies close to a track for grey extinction. The spectra show a decreasing equivalent width (EW) of the Hα$$ \mathrm{H}\alpha $$ emission line for decreasing brightness, whereas the EW of the [OI]$$ \left[\mathrm{O}I\right] $$ line increases, indicating an increased outflow activity during the obscuration. Both give further evidence for the favored theory that the obscurations are caused by a hot dusty wind emerging from the inner disk. [ABSTRACT FROM AUTHOR]

This article, titled "Eclipse Variables of UX Ori Type," is a summary of a Ph.D. dissertation by Asen Mutafov. The dissertation focuses on the extended photometric study of two stars, V1180 Cas and GM Cep, which exhibit brightness variations characteristic of the UXors type. The goal of the study is to accurately classify the variability of these stars and draw conclusions about the physical mechanisms causing the observed changes in their luminosity. The dissertation includes an introduction, six chapters, and a bibliography, with the main results presented in the last three chapters. The study finds that both stars show significant brightness variations, with GM Cep exhibiting deep brightness minima and color reversal during these minima. The variability of both stars is attributed to a combination of highly variable accretion from the circumstellar disk and obscuration by circumstellar dust particles or other features. [Extracted from the article]