Celestial Sphere Research Articles

Social Aspects of the Image of the World in Russian Folklore: Georges Dumézil and the Frog Princess

The social dominant of Russian folklore is its peasant basis, associated with the agricultural calendar. This basis is described by a system of universal semantic binary oppositions (Svetlana M. Tolstaya), which did not include social oppositions directly. In the epic, the farmer (Mikula Selyaninovich) turns out to be stronger than the warrior-hero. Wedding folklore is focused on imitation of the ancient Russian social elites (“princes”, “boyars”). The motif of the royal wedding is also connected with the fairy tale about the frog princess: the three royal sons must marry brides, who will be determined by for-tune-telling archery. The arrows of the elder brothers fall into prestigious courts, where the princely/boyar and general/merchant daughters are waiting for them. The arrow of Ivan Tsarevich falls into the swamp in the paws of a frog. This plot of archery corresponds (in the cultural anthropology of G. Dumézil) to the archaic Indo-European model of the distribution of power between three brothers ― cultural heroes who embody the three social functions (the highest is sacred, royal, the middle is military, the lowest is “economic” (providing fertility). This structure corresponds to the universal cosmologi-cal trinomial model ― the top (celestial sphere), the middle zone (the atmosphere, the earth’s surface), and the fertile chthonic bottom (soil, underworld). The trifunctional social structure is also conveyed by the spiritual “Verse on the Golubinaya kniga”, where the three estates are made from the members of the first man ― Adam. Probably, these ternary structures are associated with the archaic Indo-European model, transmitted to the Slavic tradition through the ancient mediation of the Iranian (Indo-Iranian, studied by Vladimir N. Toporov) tradition.

Expectation on observations of Fermi-LAT gamma-ray sources using the HADAR experiment

High altitude detection of astronomical radiation (HADAR) is an innovative array of atmospheric Cherenkov telescopes that employs pure water as its medium. By utilizing large-aperture hemispherical lenses, HADAR can capture atmospheric Cherenkov light, enabling the detection of gamma rays and cosmic rays in the energy range of 10 GeV to 10 TeV. Compared to traditional Imaging Atmospheric Cherenkov telescopes, HADAR offers distinct advantages such as a low energy threshold, high sensitivity, and a wide field of view. The telescope mainly consists of a hemispherical lens with a diameter of 5 m acting as a Cherenkov light collector, a cylindrical metal tank with a 4 m radius and 7 m height, and an imaging system at the bottom of the tank. The sky region covered by HADAR is much larger than the current generation of Imaging Atmospheric Cherenkov Telescopes. The field of view of HADAR can reach up to 60 degrees. Its continuous scanning capability allows for comprehensive observations of gamma-ray sources throughout the entire celestial sphere, making it an ideal instrument for studying transient and variable sources. In this study, the observational capabilities of HADAR are thoroughly investigated using the latest 4FGL-DR3 and 4LAC-DR3 gamma-ray source catalogs from Fermi-LAT. For extragalactic sources, the energy spectra in the high energy range have been extrapolated to the very high energy range, taking into account the absorption effect caused by extragalactic background light. By comparing the extrapolated results with existing VHE experimental data, the feasibility of this extrapolation method has been demonstrated. Through simulated analyses of the significance of these sources, it is anticipated that HADAR will detect a total of 93 gamma-ray sources with a significance exceeding 5 standard deviations during one year of operation. These sources comprise 45 galactic sources, 39 extragalactic sources, 3 sources of unknown type, and 6 unassociated sources.

Моделирование процесса приема собственного радиотеплового излучения земной поверхности

The receiving model of the own soil radiothermal radiation by a bipolarized microwave radiometer when remote sensing the soil moisture from an unmanned aerial vehicle on low altitude is considered. The simulation is carried out taking into account the receiving antenna pattern with side lobes. The height, speed of the carrier and the main lobe axis angle are taken into account. The main parameters of the microwave radiometer for remote determination of portraits of moistened soils are given. The Earth's surface is modeled by a two-dimensional distribution function of the soil permittivity on the thickness of the near-surface layer and a deeper layer with a different permittivity value. The two-dimensional permittivity distribution function represents as "checkerboard" with a periodic change in the permittivity of the soil by "cells". Both the proper radiothermal radiation of the soil and the relict sky radiation of the celestial sphere, re-reflected by the earth's surface, are taken into account. The perspective of using the simulation results to optimize the parameters of the radiometer and remote sensing system according to the criterion of maximum sensitivity of the system to variations in soil moisture content is analyzed.

A Consul of the Philosophers, On what is given and what is not in the Cosmos

A Byzantine text, ascribed to a “consul of the philosophers”, applies the “language of the givens” to the main circles on the celestial sphere, showing which of them are “given”, and in what sense. This text is here presented, edited, translated, and compared with its source. A discussion about the author of the text is also provided.

MOCK OBSERVATIONS OF SIMULATED STAR CLUSTER ON SOLAR ORBIT

With the advent of the Gaia DR2 catalog, which contains astrometric and photometric parameters for a large number of stars, measured with a high degree of accuracy, data about the cosmos and the Universe, including Star clusters in our Galaxy, are growing. However, when observed, the cluster stars are lost against the background of stars in the dense Galactic field. In addition, observational data alone is not sufficient to study real clusters from birth to destruction. In this regard, a number of numerical simulations of star clusters have been running to explain the processes and to determine the membership of cluster stars. And for this, we need to conduct a mock observation of model clusters. In this paper, we performed analyses on the output data from numerical simulations and developed a method for conducting mock observations of model clusters. We took one model of a star cluster with an age of 350 Myr, with a mass of 6000 , and with a star formation efficiency SFE=0.25, and put it in different galactic longitudes and at different distances from the Sun. In conclusion, using this method, we can put a cluster at any point on the celestial sphere, and this in turn allows you to compare with the real observed clusters and evaluate the possibility of detecting physical parameters in them.

Celestial Liouville theory for Yang-Mills amplitudes

We consider Yang-Mills theory with the coupling constant and theta angle determined by the vacuum expectation values of a dynamical (complex, zero mass) dilaton field. We discuss the tree-level N-gluon MHV scattering amplitudes in the presence of a nontrivial background dilaton field and construct the corresponding celestial amplitudes by taking Mellin transforms with respect to the light cone frame energies. In this way, we obtain two-dimensional CFT correlators of primary fields on the celestial sphere. We show that the celestial Yang-Mills amplitudes evaluated in the presence of a spherical dilaton shockwave are given by the correlation functions of primary field operators factorized into the holomorphic current operators times the “light” Liouville operators. They are evaluated in the semiclassical limit of Liouville theory (the limit of infinite central charge) and are determined by the classical Liouville field describing metrics on the celestial sphere.

The SPAN512 mid-latitude pulsar survey at the Nançay Radio Telescope

Context. The large number of ongoing surveys for pulsars and transients at various radio observatories is motivated by the science obtained from these sources. Timing and polarisation analysis of relativistic binaries can place strong constraints on theories of gravity. The observation of a growing number of millisecond pulsars (MSPs) spread over the celestial sphere may allow the detection of a stochastic gravitational wave background arising from supermassive black hole binaries. A more complete sample of young pulsars improves our knowledge of neutron star birth and evolution. Transients such as fast radio bursts can serve to probe the intergalactic medium. Aims. The SPAN512 pulsar survey covers intermediate Galactic latitudes using the L-band receiver of the Nançay Radio Telescope (NRT). The survey covers 224 sq. deg. of the sky for a total exposure time of 2200 h. Population syntheses predict the discovery of 3 to 19 new normal pulsars and a few MSPs. Methods. We present detailed modelling of the NRT beam with its L-band receiver and its sensitivity which we used to precisely assess the expected survey yield. We used the flexible Pulsar Arecibo L-band Feed Array data processing pipeline to search the 47 TB of SPAN512 data for pulsars and transients. Results. The SPAN512 survey discovered two new MSPs and one new middle-aged pulsar. We focus on the analysis of the 2.4-ms spin period pulsar J2205+6012 for which we also report the detection of gamma-ray pulsations. Its narrow pulse width (35µs at an observing frequency of 2.55 GHz) allows for sub-microsecond timing precision over 8 yr, with exciting prospects for pulsar timing array programs.

Digistar 6-Based Planetarium as an Educational Media for Learning about the Sun Position Using a Horizontal Coordinate System

A good understanding of the labeling of the positions of celestial bodies, including the Sun, in a horizontal coordinate system, is absolutely necessary as a basis for understanding astronomy and astrophysics. The existence of media that can be used to provide simulations of the celestial sphere and its coordinate system is very important to support the learning process. Through this quantitative descriptive statistical research with One-Group Pretest-Posttest Design, it can be shown that the use of Digistar 6-Based Planetarium as an educational medium can improve students' understanding of the position of the Sun in a horizontal coordinate system. The increase in understanding was marked by an increase in the average percentage of correct answers from pretest to posttest by 32.89%, an increase in the percentage of minimum and maximum correct answers by 54% and 60%, respectively, and an increase in the number of passes in the PAP version by 53.34%.

The Observed Polarization Direction Depending on Geometrical and Kinematic Parameters of Relativistic Jets

The study of the polarization direction is crucial in the issue of restoring the spatial structure of the magnetic field in the active galaxy parsec-scale jets. But, due to relativistic effects, the magnetic field projected onto the celestial sphere in the source reference frame cannot be assumed to be orthogonal to the observed direction of the electric vector in the wave. Moreover, the local axis of the jet component may not coincide with its motion direction, which affects the observed polarization direction. In this article, we analyze the transverse to jet distributions of the electric vector in the wave, obtained as a result of modeling with different jet kinematic and geometrical parameters for a helical magnetic field with a different twist angle and for a toroidal magnetic field in the center, surrounded by a varying thickness sheath, penetrated by a poloidal field. We obtained: 1) the shape of the electric vector transverse distribution depends in a complex way on the angles of the jet axis and the velocity vector with the line of sight; 2) ambiguity in determining the twist direction of the helical magnetic field under using only the distributions of the electric vector in the wave; 3) both considered magnetic field topologies can reproduce both the ``spine-sheath'' polarization structure and individual bright details with the longitudinal to the jet axis polarization direction.

Love and the Brethren of Purity: A Comparative Study of Human Intimacy in Islamic Philosophy

Abstract This article is a study of the Brethren of Purity’s thirty-seventh epistle, The Essence of Love. It compares this work with the treatises on love written by the Muslim philosophers Ibn Sīnā, Suhrawardī, and Mullā Ṣadrā, the leading representatives of the Peripatetic, Illuminationist, and Transcendental schools of Islamic philosophy, respectively. A fundamental distinction of the Brethren’s approach is their positive impression of love between human beings, including its romantic and conjugal components. Such love is not entirely under human control; the celestial spheres also exercise their influence. The Brethren contend that society and civilization prosper because of love. Unlike several others, they are intent on reconciling divine or “real” love with love between individuals. While the Brethren praise the benefits of romantic love and conjugal relations, Ibn Sīnā judges them harmful, and Suhrawardī a distraction. Mullā Ṣadrā, though, takes an intermediate position, influenced by both the Brethren and Ibn Sīnā.

우리나라 문화재의 3차원 모델링에 관한 수업 사례 연구

Objectives In this study, a lesson program was designed so that students in S gifted school could use GeoGebra to model 3D Korean cultural assets. The designed lessons were applied to the students, and the results were analyzed. Methods For this purpose, 14 second-year students from S gifted school located in a small city studied the functions of GeoGebra, selected Korean cultural assets by groups, and conducted mathematical modeling for 7 weeks. Afterwards, the students' results were analyzed to see how mathematical elements and convergence elements were included. Also, how the students' results can be applied to general school students is presented. Results As a result of analyzing the students' results, the mathematical elements used in the students' modeling process were polyhedra and curved surfaces. The surfaces were created by rotating curves and using GeoGebra's tools and commands. The convergence factors that appeared in the modeling process of cultural assets were the reflections of scientific knowledge and engineering knowledge. The students made celestial spheres to explain their results and experienced the models virtually in augmented reality. In addition, JavaScript coding was used to express engineering knowledge in the modeling result. Conclusions The lesson program for 3D modeling developed in this study and the results of S gifted school students can be used as basic data for 3D-based mathematical modeling classes for general school students and data for follow-up research.

Celestial Yang-Mills amplitudes and D = 4 conformal blocks

We discuss the properties of recently constructed “single-valued” celestial four-gluon amplitudes. We show that the amplitude factorizes into the “current” part and the “scalar” part. The current factor is given by the group-dependent part of the Wess-Zumino-Witten correlator of four holomorphic currents with a non-vanishing level of Kač-Moody algebra. The scalar factor can be expressed in terms of a complex integral of the Koba-Nielsen form, similar to the integrals describing four-point correlators in Coulomb gas models and, more generally, in the infinite central charge limit of Liouville theory. The scalar part can be also obtained by a dimensional reduction of a single D = 4 conformal block and the shadow block from Minkowski space to the celestial sphere.

Mapping SYK to the sky

The infrared behavior of gravity in 4D asymptotically flat spacetime exhibits a rich set of symmetries. This has led to a proposed holographic duality between the gravitational mathcal{S} -matrix and a dual field theory living on the celestial sphere. Most of our current understanding of the dictionary relies on knowledge of the 4D bulk. As such, identifying intrinsic 2D models that capture the correct symmetries and soft dynamics of 4D gravity is an active area of interest. Here we propose that a 2D generalization of SYK provides an instructive toy model for the soft limit of the gravitational sector in 4D asymptotically flat spacetime. We find that the symmetries and soft dynamics of the 2D SYK model capture the salient features of the celestial theory: exhibiting chaotic dynamics, conformal invariance, and a w1+∞ symmetry. The holographic map from 2D SYK operators to the 4D bulk employs the Penrose twistor transform.

Celestial geometry

Celestial holography expresses mathcal{S} -matrix elements as correlators in a CFT living on the night sky. Poincaré invariance imposes additional selection rules on the allowed positions of operators. As a consequence, n-point correlators are only supported on certain patches of the celestial sphere, depending on the labeling of each operator as incoming/outgoing. Here we initiate a study of the celestial geometry, examining the kinematic support of celestial amplitudes for different crossing channels. We give simple geometric rules for determining this support. For n ≥ 5, we can view these channels as tiling together to form a covering of the celestial sphere. Our analysis serves as a stepping off point to better understand the analyticity of celestial correlators and illuminate the connection between the 4D kinematic and 2D CFT notions of crossing symmetry.

Dūlāb: From Imagery to Actual Musical Instrument

Abstract Using various sources such as scores, literature, photos, interviews, and other pertinent data, this study examines the evolution of Dūlāb into a musical instrument.1 Dūlāb evolves from the concepts of Dūlāb Āsiyāb (mill wheel), Dūlāb Chāh (well wheel), and Dūlāb Falak (celestial sphere). Irrigation, mills, together with knowledge of astronomy and, finally, the conceptualization of the image in the mind of the writers and poets certainly were also the fledglings of Dūlāb in Persian culture. Here are the stages of note in the development of this musical instrument: (1) Poets’ broad employment of the word Dūlāb, although under different auspices; (2) compilation of views by Brethren of Purity (Ikhwān al-Ṣafā) as per their association of sounds with heaven by means of Dūlāb; (3) Rumi’s weaving of Dūlāb into his uber-mystical context whereby the symbolic discourse regarding it is systematically developed; (4) well wheels, mill wheels, and celestial sphere (falak) as well as spinning wheels and spinning Sufi rituals (samā‘).

Man, State, and War in Space: Neorealism and Russia’s Counterbalancing Strategy Against the United States in Outer Space Security Politics

ABSTRACT This paper aspires to contribute to the limited field of neorealist scholarship on security affairs in outer space by conducting a case study of the Russian Federation’s security policy in the celestial sphere. In recent years, Russia has emerged as one of the key players in the international politics of outer space. However, Russia’s strategy of developing its space defense assets, while in parallel launching diplomatic initiatives in international organizations calling for the avoidance of an arms race in outer space, is ambiguous. I argue that the neorealist paradigm elucidates this case by highlighting the intensifying balancing trajectories of contemporary outer space security affairs. In a first step, hypotheses on states’ behavior in the field of outer space armament and arms control are derived from the body of neorealist scholarship on terrestrial international politics. This is followed by hypothesis testing against the case of Russia’s space security politics. It is contended that Russia is engaging in a predominantly competitive endeavor vis-à-vis the United States by utilizing a hybrid approach of internal and external balancing, as well as a pragmatic instrumentalization of international institutions to leverage its own economically disadvantaged position in outer space.

Histogram-based comparison of metric spaces using HMMs

Comparison is a powerful tool for decision support. Many measures have been proposed for comparing two metric spaces, but they do not consider the data dispersion in each metric space. Furthermore, no dedicated measure has yet been proposed for comparing two metric spaces containing elements belonging to various subtypes of a global datatype. In order to attenuate the aforementioned limitations, this paper proposes a new technique for comparing two metric spaces. More formally, given a metric space X, histograms are used for performing a gradual analysis of the data dispersion inside the neighborhood of each element of X. This is a refinement of the neighborhoods’ analysis realized in an existing work. Then, another existing technique is used for associating one hidden Markov model \({\lambda }_X\) with X such that \({\lambda }_X\) learns the bin values and the visual shapes of the histograms derived from the instances in X. Meta-data derived from \({\lambda }_X\) are then saved as the components of a descriptor vector \(\overrightarrow{X}\) associated with X. Finally, the comparison between two metric spaces is performed through the comparison of their respective associated descriptor vectors using existing distance or similarity measures between two vectors. The proposed approach inherits the accuracy and the efficiency of the existing techniques on which it relies. Therefore, the experiments realized in this paper are only intended to show how it can be used for comparing particular metric spaces containing geolocations or stars in the celestial sphere.

Carrollian and celestial spaces at infinity

We show that the geometry of the asymptotic infinities of Minkowski spacetime (in d + 1 dimensions) is captured by homogeneous spaces of the Poincaré group: the blow-ups of spatial (Spi) and timelike (Ti) infinities in the sense of Ashtekar-Hansen and a novel space Ni fibering over mathcal{I} . We embed these spaces à la Penrose-Rindler into a pseudo-euclidean space of signature (d + 1, 2) as orbits of the same Poincaré subgroup of O(d + 1, 2). We describe the corresponding Klein pairs and determine their Poincaré-invariant structures: a carrollian structure on Ti, a pseudo-carrollian structure on Spi and a “doubly-carrollian” structure on Ni. We give additional geometric characterisations of these spaces as grassmannians of affine hyperplanes in Minkowski spacetime: Spi is the (double cover of the) grassmannian of affine lorentzian hyperplanes; Ti is the grassmannian of affine spacelike hyperplanes and Ni fibers over the grassmannian of affine null planes, which is mathcal{I} . We exhibit Ni as the fibred product of mathcal{I} and the lightcone over the celestial sphere. We also show that Ni is the total space of the bundle of scales of the conformal carrollian structure on mathcal{I} and show that the symmetry algebra of its doubly-carrollian structure is isomorphic to the symmetry algebra of the conformal carrollian structure on mathcal{I} ; that is, the BMS algebra. We show how to reconstruct Minkowski spacetime from any of its asymptotic geometries, by establishing that points in Minkowski spacetime parametrise certain lightcone cuts in the asymptotic geometries. We include an appendix comparing with (A)dS and observe that the de Sitter groups have no homogeneous spaces which could play the rôle that the celestial sphere plays in flat space holography.

Elements of celestial conformal field theory

In celestial holography, four-dimensional scattering amplitudes are considered as two-dimensional conformal correlators of a putative two-dimensional celestial conformal field theory (CCFT). The simplest way of converting momentum space amplitudes into CCFT correlators is by taking their Mellin transforms with respect to light-cone energies. For massless particles, like gluons, however, such a construction leads to three-point and four-point correlators that vanish everywhere except for a measure zero hypersurface of celestial coordinates. This is due to the four-dimensional momentum conservation law that constrains the insertion points of the operators associated with massless particles. These correlators are reminiscent of Coulomb gas correlators that, in the absence of background charges, vanish due to charge conservation. We supply the background momentum by coupling Yang-Mills theory to a background dilaton field, with the (complex) dilaton source localized on the celestial sphere. This picture emerges from the physical interpretation of the solutions of the system of differential equations discovered by Banerjee and Ghosh. We show that the solutions can be written as Mellin transforms of the amplitudes evaluated in such a dilaton background. The resultant three-gluon and four-gluon amplitudes are single-valued functions of celestial coordinates enjoying crossing symmetry and all other properties expected from standard CFT correlators. We use them to extract OPEs and compare them with the OPEs extracted from multi-gluon celestial amplitudes without a dilaton background. We perform the conformal block decomposition of the four-gluon single-valued correlator and determine the dimensions, spin and group representations of the entire primary field spectrum of the Yang-Mills sector of CCFT.

Physical Origin of the Dark Spot in the First Image of Supermassive Black Hole SgrA*

We elucidate the physical origin of the dark spot in the image of supermassive black hole SgrA* presented very recently by the EHT collaboration. It is argued that this dark spot, which is noticeably smaller than the classical black hole shadow, is the northern hemisphere of the event horizon globe. The classical black hole shadow is unseen in the image of SgrA*. The dark spot in the image of SgrA* is projected within the position of the classical black hole shadow on the celestial sphere. The outer boundary of this dark spot is an equator on the event horizon globe.