Celestial Positions Research Articles

Stability of exoplanetary systems retrieved from scalar time series

Abstract We propose a novel method applied to extrasolar planetary dynamics to describe the system stability. The observations in this field serve the measurements mainly of radial velocity, transit time, and/or celestial position. These scalar time series are used to build up the high-dimensional phase space trajectory representing the dynamical evolution of planetary motion. The framework of nonlinear time series analysis and Poincaré recurrences allows us to transform the obtained univariate signals into complex networks whose topology carries the dynamical properties of the underlying system. The network-based analysis is able to distinguish the regular and chaotic behaviour not only for synthetic inputs but also for noisy and irregularly sampled real world observations. The proposed scheme does not require neither n-body integration nor best fitting planetary model to perform the stability investigation, therefore, the computation time can be reduced drastically compared to those of the standard numerical methods.

The tilt of the velocity ellipsoid in the Milky Way with Gaia DR2

The velocity distribution of stars is a sensitive probe of the gravitational potential of the Galaxy, and hence of its dark matter distribution. In particular, the shape of the dark halo (e.g. spherical, oblate, or prolate) determines velocity correlations, and different halo geometries are expected to result in measurable differences. Here we explore and interpret the correlations in the (vR, vz)-velocity distribution as a function of position in the Milky Way. We selected a high-quality sample of stars from the Gaia DR2 catalogue and characterised the orientation of the velocity distribution or tilt angle over a radial distance range of [4 − 13] kpc and up to 3.5 kpc away from the Galactic plane while taking into account the effects of the measurement errors. We find that the tilt angles change from spherical alignment in the inner Galaxy (R ∼ 4 kpc) towards more cylindrical alignments in the outer Galaxy (R ∼ 11 kpc) when using distances that take a global zero-point offset in the parallax of −29 μas. However, if the amplitude of this offset is underestimated, then the inferred tilt angles in the outer Galaxy only appear shallower and are intrinsically more consistent with spherical alignment for an offset as large as −54 μas. We further find that the tilt angles do not seem to strongly vary with Galactic azimuth and that different stellar populations depict similar tilt angles. Therefore we introduce a simple analytic function that describes the trends found over the full radial range. Since the systematic parallax errors in Gaia DR2 depend on celestial position, magnitude, and colour in complex ways, it is not possible to fully correct for them. Therefore it will be particularly important for dynamical modelling of the Milky Way to thoroughly characterise the systematics in astrometry in future Gaia data releases.

Gaia Data Release 2

Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the GBP (330–680 nm) and GRP (630–1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.

Identification of activity peaks in time-tagged data with a scan-statistics driven clustering method and its application to gamma-ray data samples

Context.The investigation of activity periods in time-tagged data samples is a topic of great interest. Among astrophysical samples, gamma-ray sources are widely studied, due to the huge quasi-continuum data set available today fromFermi-LAT (FermiLarge Area Telescope) and the AGILE-GRID (Astro Rivelatore Gamma a Immagini LEggero-Gamma Ray Imaging Detector)Aims.To reveal flaring episodes of a given gamma-ray source, researchers make use of binned light curves. This method suffers from several drawbacks: the results depend on time-binning and the identification of activity periods is difficult for bins with a low signal-to-noise ratio. A different approach is investigated in this paper.Methods.We developed a general temporal-unbinned method to identify flaring periods in time-tagged data and discriminate statistically significant flares. We propose an event clustering method in one dimension to identify flaring episodes, and scan statistics to evaluate the flare significance within the whole data sample. This is a photometric algorithm. The comparison of the photometric results (e.g. photometric flux, gamma-ray spatial distribution) for the identified peaks with the standard likelihood analysis for the same period is mandatory to establish if source confusion is spoiling results.Results.The procedure can be applied to reveal flares in any time-tagged data sample. The result of the proposed method is similar to a photometric light curve, but peaks are resolved, they are statistically significant within the whole period of investigation, and peak detection capability does not suffer time-binning related issues. The study of the gamma ray activity of 3C 454.3 and of the fast variability of the Crab Nebula are shown as examples. The method can be applied for gamma-ray sources of known celestial position, for example, sources taken from a catalogue. Furthermore the method can be used when it is necessary to assess the statistical significance within the whole period of investigation of a flare from an unknown gamma-ray source. Extensive results based on this analysis method for some astrophysical problems are the subject of a forthcoming paper.

Same concept…Different terms

Most introductory physics courses begin with the concept of an object (usually a particle) having a precise position or location in space (I will not address spacetime here) relative to something else, the origin of a three-dimensional coordinate system perhaps. My experience has been that physics students are inherently at home with this concept. In astronomy, we often begin by thinking about the sky. For the purposes of this article, I will simply define it as that which we see when we look away from Earth’s surface. It appears almost as a two-dimensional plane, perhaps even a curved surface. When we look at something in the sky, we really have no sense of distance. Indeed, when astronomers need the “position” of a star or planet in the sky, the quantity is two dimensional. Because the sky appears to wrap around Earth, celestial positions can be given entirely by angular quantities. Astronomers use right ascension and declination, respectively, as analogs of terrestrial longitude and latitude. Right ascension is the angular distance eastward around the celestial equator (the projection of Earth’s equator onto the celestial sphere) from the vernal equinox (where the celestial equator and the ecliptic intersect such that the Sun is moving from the Southern Hemisphere to the Northern Hemisphere) to the object and declination is the object’s angular distance north or south of the celestial equator. So to an astronomer, for the purposes of aiming a telescope, position refers to a two-dimensional quantity because in the sky there is no direct sense of depth or distance.

Application of CCD drift-scan photoelectric technique on monitoring GEO satellites

Geosynchronous Earth Orbit (GEO) satellites are widely used because of their unique characteristics of high-orbit and remaining permanently in the same area of the sky. Precise monitoring of GEO satellites can provide a key reference for the judgment of satellite operation status, the capture and identification of targets, and the analysis of collision warning. The observation using ground-based optical telescopes plays an important role in the field of monitoring GEO targets. Different from distant celestial bodies, there is a relative movement between the GEO target and the background reference stars, which makes the conventional observation method limited for long focal length telescopes. CCD drift-scan photoelectric technique is applied on monitoring GEO targets. In the case of parking the telescope, the good round images of the background reference stars and the GEO target at the same sky region can be obtained through the alternating observation of CCD drift-scan mode and CCD stare mode, so as to improve the precision of celestial positioning for the GEO target. Observation experiments of GEO targets were carried out with 1.56-meter telescope of Shanghai Astronomical Observatory. The results show that the application of CCD drift-scan photoelectric technique makes the precision of observing the GEO target reach the level of 0.2″, which gives full play to the advantage of the long focal length of the telescope. The effect of orbit improvement based on multi-pass of observations is obvious and the prediction precision of extrapolating to 72-h is in the order of several arc seconds in azimuth and elevation.

Analysis on the experiment of satellite laser ranging of defunct Tiangong-1 spacecraft

Tiangong-1, which was launched on 29 September 2011, is the first prototype space station of China. During the past two years in its lifetime, Tiangong-1 has been visited by a series of Shenzhou spacecraft. On 21 March 2016, it had formally ended its service and now is replaced by Tiangong-2. The orbit of Tiangong-1 is about 400 km above the ground where Tiangong-2, the international space station and other satellites are located as well. The space debris is now posing great collision risk to these space assets. The satellite laser ranging (SLR) is a space tracking technique with the highest precision. Its precise data lay a solid foundation for reliable conjunction assessment. On October 2002, Greene, Mount Stromlo SLR station of Australia, announced that it was possible to track a piece of space debris of a size of 15 cm at a distance of 1250 km using the SLR technology. In 2011, both Graz SLR station of Austrian and Grasse LLR station of France succeeded in debris laser ranging data. In China, Shanghai Astronomical Observatory obtained debris laser ranging data in 2008, Yunnan Observatory in 2010 and Changchun Observatory in 2014 also obtained debris data using SLR. In 2014, Changchun Observatory observed a total of 244 space debris in altitude about 400 to 1800 km. Tiangong-1 spacecraft was equipped with corner cube reflectors (CCRs), which were designed mainly for orbital rendezvous with Shenzhou spacecraft and now provide convenience for SLR. From March to May of 2016, a coordinated laser ranging experiment on Tiangong-1 was made by Changchun Observatory (ILRS site ID: 7237) of National Astronomical Observatories, Sheshan station (ILRS site ID: 7821) of Shanghai Astronomical Observatory and Purple Mountain Observatory. Tiangong-1 has not been tracked by international laser ranging service (ILRS) and the orbit prediction of consolidated prediction format (CPF) cannot be obtained from ILRS. In general, the two line elements (TLE) of space objects can be downloaded from internet ( https://www.space- track.org) which is released by north American air defense command (NORAD). However, the TLE prediction error of Tiangong-1 (NORAD ID: 37820) is about several kilometers that is not precise enough for SLR. During the experiment, the actual prediction is provided by Purple Mountain Observatory. By the end of the experiment, data of 23 passes was obtained. Precise orbit determination is made by using the SLR data and the root mean squares (RMS) of the SLR observation residuals is about 10 cm. For one pass of scattered data, the orbit determination program is not convergent. Then combined orbit determination is made using one pass of SLR data and optical celestial position data. The relative weight of SLR data to optical data is 100:1 and the RMS of the SLR observation residuals is about 6.9 cm. The new orbit prediction is propagated from the orbit determination of SLR data and its precision is about 200–300 m. The radial precision is better than 100 m that is accurate enough for later laser ranging. In general, the experiment of satellite laser ranging to defunct Tiangong-1 spacecraft will have positive effects on precise orbit determination of both Tiangong-2 and other low earth orbit space objects.

INFLUENCE OF THE GALACTIC GRAVITATIONAL FIELD ON THE POSITIONAL ACCURACY OF EXTRAGALACTIC SOURCES

ABSTRACT We investigate the influence of random variations of the Galactic gravitational field on the apparent celestial positions of extragalactic sources. The basic statistical characteristics of a stochastic process (first-order moments, an autocorrelation function and a power spectral density) are used to describe a light ray deflection in a gravitational field of randomly moving point masses as a function of the source coordinates. We map a 2D distribution of the standard deviation of the angular shifts in positions of distant sources (including reference sources of the International Celestial Reference Frame) with respect to their true positions. For different Galactic matter distributions the standard deviation of the offset angle can reach several tens of μas (microarcsecond) toward the Galactic center, decreasing down to 4–6 μas at high galactic latitudes. The conditional standard deviation (“jitter”) of 2.5 μas is reached within 10 years at high galactic latitudes and within a few months toward the inner part of the Galaxy. The photometric microlensing events are not expected to be disturbed by astrometric random variations anywhere except the inner part of the Galaxy as the Einstein–Chvolson times are typically much shorter than the jittering timescale. While a jitter of a single reference source can be up to dozens of μas over some reasonable observational time, using a sample of reference sources would reduce the error in relative astrometry. The obtained results can be used for estimating the physical upper limits on the time-dependent accuracy of astrometric measurements.

An investigation of the reduction model power influence on the accuracy of the object’s position assessment using relative method

We investigated the influence of the reduction model power on the accuracy of the object’s position assessment using the relative method. The research considered reduction polynomials of the third and fifth power, their influence on the accuracy of the celestial object’s position assessment and distribution of reference stars in the frame. The result of the analysis showed the presence of a sinusoidal component in the dependence of the residual of parameters of celestial objects when the cubic reduction model is used. It also showed almost complete elimination of this component in case of using the fifth-power reduction model, which increased the number of reference stars in the frame’s edges as well as accuracy indicators of position assessments of celestial objects. The assessment criteria of significance of the reduction model coefficients using the Fisher's f-criteria proved the validity of application of the polynomial model with the power, that is higher than cubic. The results of the research can be used to improve the accuracy of estimation of celestial objects positions in the frame in the CCD-automated processing systems, which assess the position of objects in the entire field of view of the telescope.

基于最小损失函数法进行三视场天文定位定向的误差分析

基于最小损失函数法进行三视场天文定位定向的误差分析

Design of Special Calculator for Ship's Position Using Single Celestial Body Positioning

In order to discard some disadvantages of traditional astronomical navigation positioning, such as manual computation and time-consuming, we design a special calculator for locating ship's position, which not only make astronomical navigation positioning calculation quickly and operate instrument simply, but also convenient to carry. The system based on the theory of sun shift line positioning principle use the 32-bit microcontrollers based on ARM Cortex-M3 kernel as the core controller. In this paper, we give hardware design and software process of the system. Through actual test, the results of the testing value and actual value can tally well. Its calculation process only needs a few seconds, also could greatly improve the real-time and accuracy of positioning.

基于星图识别的空间目标快速天文定位

A fast celestial positioning method based on star identification was proposed to improve positioning accuracy and reduce positioning time. Firstly, the photographic time and angular values were acquired, and the pointing direction of boresight in geocentric inertial coordinate system was calculated by transforming a horizontal coordinate system into a geocentric inertial coordinate system with an astronomical triangle model. Then, all navigation stars and patterns in the area that the boresight pointed were extracted, and the corresponding relationship between stars in images and in the sky was established by a region star match. Finally, the celestial positioning for a space object was completed relatively by reference stars in a background according to pinhole imaging model. The experiment for an image with a FOV of 44and a resolution of 1 0241 024 shows that the course of the positioning for the space object has been greatly accelerated due to the introduction of astronomical triangle model and region star match, and the positioning speed is approximately 400 ms. On the other hand, the positing accuracy of a space target is better than 2 because the relative positioning method eliminates a lot of factors effecting the accuracy.

Was Uranus Observed by Hipparchus?

1. IntroductionAlthough Uranus was 'officially' discovered by William Herschel (1738-1822) on 13 March 1781, it had previously been sighted on 22 occasions between 1690 and 1771 by four different astronomers.' But there is reason to think that a naked-eye observation of the planet was made in Antiquity.The systematic error of -1 ° found in the longitudes of the Almagest star catalogue has raised many controversies about the identity of its author. Several ingenious theories2 have been suggested to solve the problem, favouring either Ptolemy or Hipparchus. However the key to the mystery may lie in the description of a star pattern in the constellation Virgo.All the versions of the Almagest agree about the presence of a quadrilateral in the left thigh of the Virgin, a part of the constellation Virgo located approximately three degrees northeast of Spica. While the coordinates given for the two stars forming the northern side of the quadrangle also agree, they do not for the two stars forming the southern side. The reason is obvious: there is only one star of the same brightness at the lower left corner of the figure. The purpose of this article is to show that the object (Baily 513 or Virgo 17) occupying the bottom right corner of the quadrangle was none other than the planet Uranus.The fundamental argument of this paper is the following:(1) There is a widespread consensus among experts (Toomer, Kunitzsch, Peters and Knobel, etc.) that the four stars in the quadrilateral in the left thigh of Virgo are as shown in Table 1.(2) There is an equally widespread realization within this consensus that this result is awkward and troubling. The quadrilateral does not look like a quadrilateral, and the coordinates do not match well for the supposed Virgo 17 = 76 Vir (see Figure 1 (left)).(3) There is a simple way to fix things. For Virgo 19, read s = -4 rather than -3, in agreement with a couple of Almagest manuscripts. Then the Vir 19 coordinates match very well to 76 Vir.(4) But then what matches to Virgo 17? There is a very good match in coordinates and magnitude to Virgo 17 if we assume that this celestial body was the planet Uranus observed by Hipparchus about 128 b.c., and the quadrilateral is now more apparent (see Figure 1 (right)).In Tables 1 and 2, Flamsteed numbers are used in column Identity; visual magnitudes are indicated in column V; and the resulting errors are given in arc minutes. As will be discussed in more detail below, the versions of the Almagest supporting the Uranus solution are the so-called Arabic versions while those favouring the Consensus solution are Greek.In the remainder of this article, all dates are in the Julian calendar and unless otherwise stated, the years before Christ are written in the manner of astronomers (for instance 128 b.c. corresponds to -127), celestial positions are referred to the mean equinox of the year -128.0 and the time scale used is Universal Time.2. The Quadrilateral in the Left Thigh of the VirginBefore examining the appearance and the localization of this asterism in detail, let us first attempt to define the term quadrilateral (in Greek isiparcAsupov) which is rather puzzling because this shape may designate any convex polygon with four sides. The whole of the star catalogue found in Books 7 and 8 of the Almagest contains 14 such figures of which 12 are clearly identifiable. Among these 12 figures, 6 refer to a rectangle (Dra, Lep, Psc, Ser, UMa, UMi), 4 to a trapezium (Cet, Cnc, Ori, Sgr), 1 to a rhombus (Del), and 1 to a parallelogram (Tau) formed by four stars of nearly the same brightness. Apart from the unresolved quadrangle in Virgo, another ambiguous figure lies in the constellation Cetus. However, in that case, the problem is due the presence of several candidate stars in the vicinity.This clarification made, let us now settle the position of the quadrangle with the help of two different celestial charts: an ancient and a modern one. …

A simple procedure to extend the Gauss method of determining orbital parameters from three to N points

A simple procedure is developed to determine orbital elements of an object orbiting in a central force field which contribute more than three independent celestial positions. By manipulation of formal three point Gauss method of orbit determination, an initial set of heliocentric state vectors ${\bf r}_i$ and $\dot{\bf{r}}_i$ is calculated. Then using the fact that the object follows the path that keep the constants of motion unchanged, I derive conserved quantities by applying simple linear regression method on state vectors ${\bf r}_i$ and $\dot{\bf{r}}_i$. The best orbital plane is fixed by applying an iterative procedure which minimize the variation in magnitude of angular momentum of the orbit. Same procedure is used to fix shape and orientation of the orbit in the plane by minimizing variation in total energy and Laplace Runge Lenz vector. The method is tested using simulated data for a hypothetical planet rotating around the sun.

HATSouth: A Global Network of Fully Automated Identical Wide-Field Telescopes11The HATSouth hardware was acquired by NSF MRI NSF/AST-0723074 and is owned by Princeton University. The HATSouth network is operated by a collaboration consisting of Princeton University (PU), the Max Planck Institute for Astronomy (MPIA), and the Australian National University (ANU). The station at Las Campanas Observatory (LCO), of the Carnegie

ABSTRACTHATSouth is the world’s first network of automated and homogeneous telescopes that is capable of year-round 24 hr monitoring of positions over an entire hemisphere of the sky. The primary scientific goal of the network is to discover and characterize a large number of transiting extrasolar planets, reaching out to long periods and down to small planetary radii. HATSouth achieves this by monitoring extended areas on the sky, deriving high precision light curves for a large number of stars, searching for the signature of planetary transits, and confirming planetary candidates with larger telescopes. HATSouth employs six telescope units spread over three prime locations with large longitude separation in the southern hemisphere (Las Campanas Observatory, Chile; HESS site, Namibia; Siding Spring Observatory, Australia). Each of the HATSouth units holds four 0.18 m diameter f/2.8 focal ratio telescope tubes on a common mount producing an 8.2° × 8.2° field of view on the sky, imaged using four 4 K × 4 K CCD cameras and Sloan r filters, to give a pixel scale of 3.7″ pixel-1. The HATSouth network is capable of continuously monitoring 128 square arc degrees at celestial positions moderately close to the anti-solar direction. We present the technical details of the network, summarize operations, and present detailed weather statistics for the three sites. Robust operations have meant that on average each of the six HATSouth units has conducted observations on ∼500 nights over a 2 years time period, yielding a total of more than 1 million science frames at a 4 minute integration time and observing ∼10.65 hr day-1 on average. We describe the scheme of our data transfer and reduction from raw pixel images to trend-filtered light curves and transiting planet candidates. Photometric precision reaches ∼6 mmag at 4 minute cadence for the brightest non-saturated stars at r ≈ 10.5. We present detailed transit recovery simulations to determine the expected yield of transiting planets from HATSouth. We highlight the advantages of networked operations, namely, a threefold increase in the expected number of detected planets, as compared to all telescopes operating from the same site.

SEARCHING FOR COMETS ON THE WORLD WIDE WEB: THE ORBIT OF 17P/HOLMES FROM THE BEHAVIOR OF PHOTOGRAPHERS

We performed an image search for "Comet Holmes," using the Yahoo Web search engine, on 2010 April 1. Thousands of images were returned. We astrometrically calibrated---and therefore vetted---the images using the Astrometry.net system. The calibrated image pointings form a set of data points to which we can fit a test-particle orbit in the Solar System, marginalizing over image dates and detecting outliers. The approach is Bayesian and the model is, in essence, a model of how comet astrophotographers point their instruments. In this work, we do not measure the position of the comet within each image, but rather use the celestial position of the whole image to infer the orbit. We find very strong probabilistic constraints on the orbit, although slightly off the JPL ephemeris, probably due to limitations of our model. Hyperparameters of the model constrain the reliability of date meta-data and where in the image astrophotographers place the comet; we find that ~70 percent of the meta-data are correct and that the comet typically appears in the central third of the image footprint. This project demonstrates that discoveries and measurements can be made using data of extreme heterogeneity and unknown provenance. As the size and diversity of astronomical data sets continues to grow, approaches like ours will become more essential. This project also demonstrates that the Web is an enormous repository of astronomical information; and that if an object has been given a name and photographed thousands of times by observers who post their images on the Web, we can (re-)discover it and infer its dynamical properties.

偏振光天文导航定位能力分析

Based on the polarization of skylight,the polarized light celestial positioning will have great application value when it has little position error.According to skylight polarization detection modle and single body celestial positioning modle,the polarized light celestial positioning error modle was built.Based on this model,the sensitivity of skylight polarization angle and sun direction was given,and the precision of polarized light celestial positioning was calculated.Analyzing results show that: 1)polarized light celestial positioning result will be better if the polarized direction detected on ship changes faster,so the detecting sensor can be set in the right direction according to the course,sun′s height and orientation;2)the precision of polarized light celestial positioning system can reach NM level when the detecting precision of polarization angle achieves angle cent level.

Simultaneous celestial positioning and orientation for the lunar rover

In order to obtain absolute heading angle and position, lunar rover needs the support of autonomous celestial navigation system (CNS). This paper proposes a sun observation based simultaneous celestial positioning and orientation (SCPO) algorithm for the lunar rover under stationary position. Firstly we measure the sun orientation by a sun sensor and the gravity orientation by an inclinometer; secondly combine them with sun ephemeris; finally solve this problem with quaternion estimation (QUEST). By analyzing affects of the sensor's system error (such as the installation errors, bias, etc.) and random noise under stationary conditions, these two types of errors can be eliminated using joint calibration. Executing the SCPO on the moon is demonstrated through simulation. The algorithm is carried out with an experiment on the earth surface, and results demonstrate the high consistency of our simulation.

The binary companion of PSR J1740−3052

Abstract We report on the identification of a near-infrared counterpart to the massive (>11 M⊙) binary companion of pulsar J1740−3052. An accurate celestial position of PSR J1740−3052 is determined from interferometric radio observations. Adaptive optics corrected near-infrared imaging observations show a counterpart at the interferometric position of the pulsar. The counterpart has Ks= 15.87 ± 0.10 and J−Ks > 0.83. Based on distance and absorption estimates from models of the Galactic electron and dust distributions, these observed magnitudes are consistent with those of a main-sequence star as the binary companion. We argue that this counterpart is the binary companion to PSR J1740−3052 and thus rule out a stellar mass black hole as the pulsar companion.

Discussions of Astrology in Early Tafsīr

Judicial astrology, predicting future events on the basis of celestial positions, has been a fraught topic in Islamic literature. On one hand, the spectre of humans knowing their future with certainty would weaken the principle of human responsibility. On the other hand, given God's omnipotence, it would be entirely possible that the heavens were a means for God's control over the earth. Previous research on religious reactions to astrology in Islamic civilisation has used Ḥadīth and Kalām texts to conclude that the prevailing attitude was one of disapproval. My current research uses Tafsīr literature to argue that this attitude of disapproval was far more nuanced. This paper will first survey what early Tafsīr has said about astrology and, second, present late antique Jewish and Christian texts that could be the sources or context for the views on astrology found in early Tafsīr. To help explain some of the differences between early Tafsīr's view of astrology and early Kalām's view of astrology, the third section of this article covers certain statements made in early astrology texts in Islamic civilisation, texts composed, most likely, after the discussions of astrology in early Tafsīr. Fourth, I will present some early reactions of mutakallimūn to astrology. I will conclude that discussions of astrology in early Tafsīr, as well as most Islamic literature dating from before 287/900, were not concerned with astrology's causal framework, or even with predictions in principle, but rather with a defense of prophecy. I will also argue that the discussions of astrology in early Tafsīr were not as critical as the reactions of the early mutakallimūn to astrology.