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In 1588 Tycho Brahe proposed a new cosmological system keeping a motionless Earth at the centre of the world. In the first half of the following century the reception of Tycho's model within the Society of Jesus was characterized by a strong resistance at the beginning, followed by a long and winding path, and then a good fortune, whereas heliocentric models were increasingly investigated in European observatories. In 1651 a Jesuit astronomer, Giovan Battista Riccioli, published the Almagestum novum, an encyclopaedic synthesis of astronomical knowledge where the Earth's motions or rest were extensively discussed in order to prove the Earth's immobility. However, through the period 1650–1687 the Almagestum novum did not entirely fulfil its aims, rather seeming like the dying swan's song of Tychonic or semi-Tychonic models. Contemporary scholars appreciated the encyclopaedic effort by Riccioli, but many were critical of his proofs. Even influential Jesuit astronomers showed a remarkable interest in the Copernican model, accepting geocentric models only on the basis of Holy Scripture's authority. This conduct and the tacitly allowed circulation in Catholic Europe of openly Copernican books, indicate that Catholic science tolerated heliocentric theory, when presented as a computational device rather than a representation of reality, more frequently than we usually think. [ABSTRACT FROM AUTHOR]

This paper analyzes the locally-optimal heliocentric transfer of a spacecraft propelled by an electric solar wind sail, an innovative propellantless propulsion system that generates a propulsive acceleration exploiting the momentum of solar wind particles. The potentialities of such an advanced thruster are investigated in terms of flight times required to achieve a given heliocentric orbit. The problem is addressed using a locally-optimal formulation, by minimizing a scalar performance index that depends on the time derivatives of the osculating orbital elements. The proposed algorithm gives an estimate of the globally-optimal flight time with reduced computational efforts compared to a traditional optimization approach. Also, when the performance index involves a single orbital parameter and the transfer trajectory is two-dimensional, the proposed approach provides an analytical solution to the locally-optimal control problem. The procedure discussed in the paper is used to quantify the near-optimal performance of an electric solar wind sail in some advanced mission scenarios, such as the design of a heliocentric non-Keplerian orbit for solar activity monitoring, the exploration of the Solar System boundaries, and the rendezvous with comets 1P Halley and 67P/Churyumov-Gerasimenko. [ABSTRACT FROM AUTHOR]

We make the first attempt to find dwarf galaxies in eight Fermi -LAT extended, unassociated, source fields using Gaia DR2. After probing previously unexplored heliocentric distances of d < 20 kpc with an extreme-deconvolution (XD) technique, we find no sign of a dwarf galaxy in any of these fields despite Gaia 's excellent astrometric accuracy. Our detection limits are estimated by applying the XD method to mock data, obtaining a conservative limit on the stellar mass of M * < 104 M⊙ for d < 20 kpc. Such a low stellar mass implies either a low-mass subhalo or a massive stripped-down subhalo. We use an analytic model for stripped subhaloes to argue that, given the sizes and fluxes of the Fermi -LAT sources, we can reject the hypothesis that they owe to dark matter annihilation. [ABSTRACT FROM AUTHOR]

We present an analysis of the photometric and spectroscopic data of the comet C/2012 S1 (ISON) observed at the heliocentric distances of 6.21–4.81 AU. The photometric observations were made with the 60-cm Zeiss-600 telescope (ICAMER, peak Terskol, Russia) and the spectroscopic observations were performed using the SCORPIO-2 focal reducer mounted in the prime focus of the 6-m BTA telescope (SAO RAS, Russia). We analyse the B, V and R-band images to describe the dusty cometary coma and to investigate its brightness, colours and dust production rate. The spectra cover the wavelength range of 3600–7070 Å. No emissions which are expected in this wavelength region were detected above the 3σ level. The continuum shows a reddening effect with the normalized gradient of reflectivity along dispersion of 9.3 ± 1.1% per 1000 Å. A dust-loss rate was derived using the obtained values and under the different model assumptions. Our simulations clearly indicate that to retrieve dust production from the observational Afρ parameter is an ambiguous task. The result of such a procedure is strongly dependent on dynamical (e.g. effective density and cross-section) as well as optical (e.g. scattering coefficient and phase function) characteristics of dust grains. A variation of the mentioned parameters can lead to dramatic changes in the evaluation of mass production. We demonstrate that the dynamic and optical properties are interconnected via the microscopic properties of dust grains (effective size and porosity). [ABSTRACT FROM AUTHOR]

Over the past decade there has been a large increase in the number of automated camera networks that monitor the sky for fireballs. One of the goals of these networks is to provide the necessary information for linking meteorites to their pre-impact, heliocentric orbits and ultimately to their source regions in the solar system. We re-compute heliocentric orbits for the 25 meteorite falls published to date from original data sources. Using these orbits, we constrain their most likely escape routes from the main asteroid belt and the cometary region by utilizing a state-of-the-art orbit model of the near-Earth-object population, which includes a size-dependence in delivery efficiency. While we find that our general results for escape routes are comparable to previous work, the role of trajectory measurement uncertainty in escape-route identification is explored for the first time. Moreover, our improved size-dependent delivery model substantially changes likely escape routes for several meteorite falls, most notably Tagish Lake which seems unlikely to have originated in the outer main belt as previously suggested. We find that reducing the uncertainty of fireball velocity measurements below  ∼ 0.1 km/s does not lead to reduced uncertainties in the identification of their escape routes from the asteroid belt and, further, their ultimate source regions. This analysis suggests that camera networks should be optimized for the largest possible number of meteorite recoveries with measured speed precisions of order 0.1 km/s. [ABSTRACT FROM AUTHOR]

The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). ThreeGCs (NGC 6341, NGC 7078, and ω Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galactic disk. The passage of any one of these three GCs through the disk could potentially have initiated the formation of the Gould Belt. [ABSTRACT FROM AUTHOR]

Spectroscopic observations of comet 29P/Schwassmann-Wachmann 1 were carried out at the SOAR 4.1-meter telescope (Chile) on August 12, 2016, when its heliocentric distance was 5.9 au. The spectra revealed CO + and N 2 + emissions in the cometary coma. The [ N 2 + ]/[CO + ] ratio within the projected slit seems to be 0.01. The mean value of the normalized spectral gradient is 12.69 ± 0.06 for spectral range 3448–5260 Å. [ABSTRACT FROM AUTHOR]

We use the Sloan Digital Sky Survey (SDSS)-Gaia Catalogue to identify six new pieces of halo substructure. SDSS-Gaia is an astrometric catalogue that exploits SDSS data release 9 to provide first epoch photometry for objects in the Gaia source catalogue. We use a version of the catalogue containing 245 316 stars with all phase-space coordinates within a heliocentric distance of ~10 kpc.We devise a method to assess the significance of halo substructures based on their clustering in velocity space. The two most substantial structures are multiple wraps of a stream which has undergone considerable phase mixing (S1, with 94 members) and a kinematically cold stream (S2, with 61 members). The member stars of S1 have a median position of (X, Y, Z) = (8.12, -0.22, 2.75) kpc and a median metallicity of [Fe/H] = -1.78. The stars of S2 have median coordinates (X, Y, Z) = (8.66, 0.30, 0.77) kpc and a median metallicity of [Fe/H] = -1.91. They lie in velocity space close to some of the stars in the stream reported by Helmi et al. By modelling, we estimate that both structures had progenitors with virial masses ≈1010M☉ and infall times ≳ 9 Gyr ago. Using abundance matching, these correspond to stellar masses between 106 and 107M☉. These are somewhat larger than the masses inferred through the mass-metallicity relation by factors of 5 to 15. Additionally, we identify two further substructures (S3 and S4 with 55 and 40 members) and two clusters or moving group (C1 and C2 with 24 and 12) members. In all six cases, clustering in kinematics is found to correspond to clustering in both configuration space and metallicity, adding credence to the reliability of our detections. [ABSTRACT FROM AUTHOR]

The article presents the results of the observation of a strong magnetic storm and two X-ray flares during the summer solstice in 2015, and their impact on the HF signals characteristics in ionospheric oblique sounding. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, ultimately causing a long blackout on paths adjacent to subauroral latitudes. On mid-latitude paths, the decrease in 1FMOF reached ∼50% relative to the average values for the quiet ionosphere. It is shown that the propagation conditions via the sporadic Es layer during the magnetic storm on a subauroral path are substantially better than those for F-mode propagation via the upper ionosphere. The delay of the sharp decrease in 1FMOF during the main phase of the magnetic storm allowed us to determine the propagation velocity of the negative phase disturbances (∼100 m/s) from subauroral to mid-latitude ionosphere along two paths: Lovozero – Yoshkar-Ola and Cyprus – Nizhny Novgorod. It is shown that both the LOF and the signal/noise ratio averaged over the frequency band corresponding to the propagation mode via the sporadic Es layer correlate well with the auroral AE index. Using an over-the-horizon chirp radar with a bistatic configuration on the Cyprus – Rostov-on-Don path, we located small-scale scattering irregularities responsible for abnormal signals in the region of the equatorial boundary of the auroral oval. [ABSTRACT FROM AUTHOR]

Context. The thermal properties of the surfaces of asteroids determine the magnitude of the drift rate cause by the Yarkovsky force. In the general case of Main Belt asteroids, the Yarkovsky force is indirectly proportional to the thermal inertia, Г. Aims. Following the proposed relationship between Г and asteroid diameter D, we find that asteroid's Yarkovsky drift rates might have a more complex size dependence than previous thought, leading to a curved family V-shape boundary in semi-major axis, a, vs. 1/D space. This implies that asteroids are drifting faster at larger sizes than previously considered decreasing on average the known ages of asteroid families. Methods. The V-Shape curvature is determined for >25 families located throughout the Main Belt to quantify the Yarkovsky sizedependent drift rate. Results. We find that there is no correlation between family age and V-shape curvature. In addition, the V-shape curvature decreases for asteroid families with larger heliocentric distances suggesting that the relationship between Г and D is weaker in the outer MB possibly due to homogenous surface roughness among family members. [ABSTRACT FROM AUTHOR]

Context. The systematic investigation of comets in a wide range of heliocentric distances can contribute to a better understanding of the physical mechanisms that trigger activity at large distances from the Sun and reveals possible differences in the composition of outer solar system bodies belonging to various dynamical groups. Aims. We seek to analyze the dust environment of the selected nearly isotropic comets with a perihelion distance between 4.5 and 9.1 au, where sublimation of water ice is considered to be negligible. Methods. We present results of multicolor broadband photometric observations for 14 distant active objects conducted between 2008 and 2015 with various telescopes. Images obtained with broadband filters were used to investigate optical colors of the cometary comae and to quantify physical activity of the comet nuclei. Results. The activity level was estimated with Af ± parameters ranging between 95 ± 10 cm and 9600 ± 300 cm. Three returning comets were less active than the dynamically new comets. Dust production rates of the comet nuclei were estimated between 1 and 100 kg s±1 based on some assumptions about the physical properties of dust particles populating comae. The measured colors point out reddening of the continuum for all the comets. The mean values of a normalized reflectivity gradient within the group of the comets amount to 14 ± 2% per 1000 Å and 3 ± 2% per 1000 Å in the BV and VR spectral domains, respectively. The comae of the dynamically new comets, which were observed on their inbound legs, may be slightly redder in the blue spectral interval than comae of the comets observed after the perihelion passages. The dynamically new comets observed both pre- and post-perihelion, seem to have higher production rates post-perihelion than pre-perihelion for similar heliocentric distances. [ABSTRACT FROM AUTHOR]

Earth-Mars cycling spacecraft have been proposed as potentially beneficial to Mars exploration. There are many types of cyclers, but their common characteristic is that they have a heliocentric trajectory that brings them close to both Earth and Mars at regular intervals. As usually envisioned, a large cycler spacecraft would conast of most of the required mass (for example, for life support), and the crew would travel to and from both planet; in a smaller "taxi" vehicle. The taxi vehicle trajectories would necessarily be hyperbolic; such trajectories have not received as much attention as the cycler trajectories but, unless they can be flown with reasonable propellant consumption and safety, the cycler concept is not feasible. In this work, propellant-minimizing transfers are f >und for both impulsive and low-thrust hyperbolic rendezvous. A heuristic method, called particle swarm, is used fcr the global optimization. [ABSTRACT FROM AUTHOR]

Based on the high spectral resolution monitoring conducted at the 6-m BTA telescope, we study the optical spectrum of the high-latitude variable V534 Lyr. Heliocentric radial velocities Vr corresponding to the positions of all metal absorption components, as well as the Na I D and Hα lines were measured during all the observational sets. The analysis of the velocity field examining the lines of various nature revealed a low-amplitude variability of Vr based on the lines with a high excitation potential, which are formed in deep layers of the stellar atmosphere, and allowed to estimate the systemic velocity of Vsys ≈ −125 kms−1 (Vlsr ≈ −105 kms−1). The distance estimate of d ≈ 6 kpc for the star leads to its absolute magnitude of MV≈−5⋅m3, what corresponds to the spectral classification. The previously undetected spectral phenomenon was revealed for this star: at certain times a splitting of the profiles of low-excited absorptions is observed, reaching ΔVr = 20-50 kms−1. A combination of the parameters: reduced metallicity [Met/H]⊙ = −0.28, high nitrogen abundance [N/Fe] = +1.10, large spatial velocity, high luminosity, a strong variability of the emission-absorption profiles of HI lines, splitting of metal absorptions at different times of observations and the variability of the velocity field in the atmosphere allow to classify V534 Lyr as a pulsating star in the thick disk of our Galaxy. [ABSTRACT FROM AUTHOR]

The problem of capturing a spacecraft from a heliocentric orbit into a high parking orbit around binary asteroids is investigated in the current study. To reduce the braking $\Delta V$ , a new capture strategy takes advantage of the three-body gravity of the binary asteroid to lower the inertial energy before applying the $\Delta V$ . The framework of the circular restricted three-body problem (CR3BP) is employed for the binary asteroid system. The proposed capture strategy is based on the mechanism by which inertial energy can be decreased sharply near zero-velocity curves (ZVCs). The strategy has two steps, namely, hitting the target ZVC and raising the periapsis by a small $\Delta V$ at the apoapsis. By hitting the target ZVC, the positive inertial energy decreases and becomes negative. Using a small $\Delta V$ , the spacecraft inserts into a bounded orbit around the asteroid. In addition, a rotating mass dipole model is employed for elongated asteroids, which leads to dynamics similar to that of the CR3BP. With this approach, the proposed capture strategy can be applied to elongated asteroids. Numerical simulations validate that the proposed capture strategy is applicable for the binary asteroid 90 Antiope and the elongated asteroid 216 Kleopatra. [ABSTRACT FROM AUTHOR]

Based on long-term spectral monitoring with high spectral resolution, the optical spectrum of the weak central star of the IR source RAFGL 5081 has been studied for the first time. The spectral type of the star is close to G5-8 II, and its effective temperature is T ≈ 5400 K. An unusual spectral phenomenon was discovered: splitting of the profiles of broad, stationary absorption lines of medium and low intensity. The heliocentric radial velocities V of all components of metal absorption lines, the Na I D lines, and the Hα line were measured for all the observation epochs. The constancy of the absorption lines rules out the possibility that the line splitting is due to binarity. The radial velocities of the wind components in the profiles of the Na I D and Hα lines reach −250 and −600 km/s, respectively. These profiles have narrow components, whose number, depth, and position vary with time. The time variability and multicomponent structure of the profiles of the Na I D and Hα lines indicates inhomogeneity and instability of the circumstellar envelope of RAFGL 5081. The presence of components with velocity V (IS) = −65 km/s in the Na I (1) lines provides evidence that RAFGL 5081 is located behind the Perseus arm, i.e, no closer than 2 kpc. It is noted that RAFGL 5081 is associated with the reflection nebula GN 02.44.7. [ABSTRACT FROM AUTHOR]

We present a geometrical methodology for analyzing the formation flying of electric solar wind sail based spacecraft that operate in heliocentric, elliptic, displaced orbits. The spacecraft orbit is maintained by adjusting its propulsive acceleration modulus, whose value is estimated using a thrust model that takes into account a variation of the propulsive performance with the sail attitude. The properties of the relative motion of the spacecraft are studied in detail and a geometrical solution is obtained in terms of relative displaced orbital elements, assumed to be small quantities. In particular, for the small eccentricity case (i.e. for a near-circular displaced orbit), the bounds characterized by the extreme values of relative distances are analytically calculated, thus providing an useful mathematical tool for preliminary design of the spacecraft formation structure. [ABSTRACT FROM AUTHOR]

We have investigated nucleosynthetic Mo isotope anomalies in 38 different bulk iron meteorites from 11 groups, to produce by far the largest and most precise dataset available to date for such samples. All magmatic iron groups were found to display deficits in s-process Mo isotopes, with essentially constant anomalies within but significant variations between groups. Only meteorites of the non-magmatic IAB/IIICD complex revealed terrestrial Mo isotopic compositions. The improved analytical precision achieved in this study enables two isotopically distinct suites of iron meteorites to be identified. Of these, the r=p suite encompasses the IC, IIAB, IIE, IIIAB, IIIE and IVA groups and exhibits relatively modest but ‘pure’ s-process deficits, relative to Earth. The second r>p suite includes groups IIC, IIIF and IVB. These iron meteorites show larger s-process deficits than the r=p suite , coupled with an excess of r-process relative to p-process components. Comparison of the results with data for other elements (e.g., Cr, Ni, Ru, Ti, Zr) suggests that the Mo isotope variability is most likely produced by thermal processing and selective destruction of unstable presolar phases. An updated model is proposed, which relates the iron meteorite suites to different extents of thermal processing in the solar nebula, as governed by heliocentric distance. In detail, the r=p suite of iron meteorite parent bodies is inferred to have formed closer to the Sun, where the extent of thermal processing was similar to that experienced by terrestrial material, so that the meteorites exhibit only small s-process deficits relative to Earth. In contrast, the r>p suite formed at greater heliocentric distance, where more subtle thermal processing removed a smaller proportion of r- and p-process host phases, thereby generating larger s-process deficits relative to the terrestrial composition. In addition, the thermal conditions enabled selective destruction of p- versus r-isotope carrier phases, to produce the observed divergence of r- and p-process Mo isotope abundances. [ABSTRACT FROM AUTHOR]

Meteor showers are recognized from the concentration of their radiant distribution on the celestial sphere, and their similar speeds. It has been pointed out that the dispersion of the radiants depends on the velocity of and the spread in velocities between individual stream meteoroids. For meteor showers with low speeds at the Earth, the dispersion can become so large that the shower becomes hard to recognize (Sato and Watanabe, 2014). In this paper, we apply a technique described in Sato and Watanabe (2014) which transforms radiants from a geocentric to a heliocentric frame. The technique is applied to detect two low speed meteor showers, the Phoenicids and the June Bootids, which otherwise would be very difficult to recognize as true meteor showers. [ABSTRACT FROM AUTHOR]

A very bright bolide illuminated the sky over Denmark and neighboring countries on February 6th, 2016 at 21:07:18-23UT. It terminated by a multiple meteorite fall in the heavily populated area of the western outskirts of Copenhagen. Several meteorites classified as the H5/6 ordinary chondrites have been found shortly after the fall and total recovered mass reached almost 9 kg (Haack, 2016). Although this spectacular bolide has been reported by many casual witnesses, the instrumental records are very scarce, mainly due to bad weather over Denmark and neighboring countries. Despite it we were able to collect five instrumental records taken from different locations which were useful for the analysis of this event. We used three high resolution digital photographic images taken in Germany, one high resolution radiometric light curve taken by the northernmost Czech automated fireball observatory and one video record taken by a surveillance camera on the Danish west coast where a part of the fireball trajectory was recorded. It allowed us to reliably determine basic parameters defining the luminous trajectory of the bolide in the atmosphere and also heliocentric orbit of the initial meteoroid causing this spectacular meteorite fall. We found that this event was caused by a relatively fragile 50 cm meteoroid with initial mass about 250 kg. It entered the atmosphere with velocity of 14.5 km s −1 and quite steep entry angle of 62°. Its luminous flight started at 85.5 km and after 76 km long trajectory it terminated at 18.3 km. The heliocentric orbit of this meteoroid was of Apollo type with low inclination of 1° and perihelion distance just inside the Earth's orbit. It had a relatively large semimajor axis of 2.8 AU and aphelion distance 4.64 AU. It is the second largest aphelion distance among all meteorites with known orbits and the orbit had the same character as that of the Košice meteorite (H5 ordinary chondrite), which fell on February 28, 2010 (Borovička et al., 2013). [ABSTRACT FROM AUTHOR]

Since almost all de-excitation lines from nuclear states excited by flare-accelerated protons and $\alpha $ -particles are emitted promptly after nuclear collisions, the emission photon's energy depends on the velocity of the recoiling nucleus. The energies and widths of $\gamma $ -ray lines provide a wealth of information on the directionality and spectra of ions in solar flares. In this paper, we use TALYS code to improve the cross sections of $\gamma $ -ray lines production, and calculate the shapes of the 1.634 MeV line from de-excitation of Ne as a function of ion's energy spectra and the heliocentric angle. Taking this line shape as an example, we try to develop a new method of line shape analysis to study the properties of accelerated ions in solar flares. [ABSTRACT FROM AUTHOR]

In the framework of the planar and circular restricted three-body problem, we consider an asteroid that orbits the Sun in quasi-satellite motion with a planet. A quasi-satellite trajectory is a heliocentric orbit in co-orbital resonance with the planet, characterized by a nonzero eccentricity and a resonant angle that librates around zero. Likewise, in the rotating frame with the planet, it describes the same trajectory as the one of a retrograde satellite even though the planet acts as a perturbator. In the last few years, the discoveries of asteroids in this type of motion made the term 'quasi-satellite' more and more present in the literature. However, some authors rather use the term 'retrograde satellite' when referring to this kind of motion in the studies of the restricted problem in the rotating frame. In this paper, we intend to clarify the terminology to use, in order to bridge the gap between the perturbative co-orbital point of view and the more general approach in the rotating frame. Through a numerical exploration of the co-orbital phase space, we describe the quasi-satellite domain and highlight that it is not reachable by low eccentricities by averaging process. We will show that the quasi-satellite domain is effectively included in the domain of the retrograde satellites and neatly defined in terms of frequencies. Eventually, we highlight a remarkable high eccentric quasi-satellite orbit corresponding to a frozen ellipse in the heliocentric frame. We extend this result to the eccentric case (planet on an eccentric motion) and show that two families of frozen ellipses originate from this remarkable orbit. [ABSTRACT FROM AUTHOR]

Long-exposure fireball photographs have been used to systematically record meteoroid trajectories, calculate heliocentric orbits, and determine meteorite fall positions since the mid-20th century. Periodic shuttering is used to determine meteoroid velocity, but up until this point, a separate method of precisely determining the arrival time of a meteoroid was required. We show it is possible to encode precise arrival times directly into the meteor image by driving the periodic shutter according to a particular pattern-a de Bruijn sequence-and eliminate the need for a separate subsystem to record absolute fireball timing. The Desert Fireball Network has implemented this approach using a microcontroller driven electro-optic shutter synchronized with GNSS UTC time to create small, simple, and cost-effective high-precision fireball observatories with submillisecond timing accuracy. [ABSTRACT FROM AUTHOR]

The article discusses the use of microelectromechanical system to proposed the distribution of sensing nodes in heliocentric orbit, wherein it mentions the orbit evolution can be controlled through through modulation. It mentions the use of partial differential equations (PDEs), akin to fluid mechanics dealing with continuum flow, and ordinary differential equations (ODEs) to model orbit revolution in astrodynamics.

With the new Tycho- Gaia Astrometric Solution (TGAS), I derive a new parallactic distance to the young σ Orionis open cluster, which is a cornerstone region for studying the formation and evolution of stars and substellar objects from tens of solar masses to a few Jupiter masses. I started with the list of the 46 brightest cluster stars of Caballero (2007). After identifying the 24 TGAS stars in the 30 arcmin-radius survey area and accounting for 11 FGKM-type dwarfs and giants in the foreground and background, I got a list of 13 cluster members and candidates with new parallaxes. Of them, I discarded five cluster member candidates with questionable features of youth and/or discordant parallaxes and proper motions, including a distant Herbig Ae/Be star, and proceeded with the remaining eight stars. The σ Orionis mean heliocentric distance is [ABSTRACT FROM AUTHOR]

Based on published data, we have produced a sample of planetary nebulae (PNe) that is complete within 2 kpc of the Sun. We have estimated the total number of PNe in the Galaxy from this sample to be 17 000±3000 and determined the vertical scale height of the thin disk based on an exponential density distribution to be 197 ± 10 pc. The next sample includes PNe from the Stanghellini-Haywood catalog with minor additions. For this purpose, we have used ~200 PNe with Peimbert's types I, II, and III. In this case, we have obtained a considerably higher value of the vertical scale height that increases noticeably with sample radius. We have experimentally found that it is necessary to reduce the distance scale of this catalog approximately by 20%. Then, for example, for PNe with heliocentric distances less than 4 kpc the vertical scale height is 256 ± 12 kpc. A kinematic analysis has confirmed the necessity of such a reduction of the distance scale. [ABSTRACT FROM AUTHOR]

Context. On 20 January 2015 the Rosetta spacecraft was at a heliocentric distance of 2.5AU, accompanying comet 67P/Churyumov- Gerasimenko on its journey toward the Sun. The Ion Composition Analyser (RPC-ICA), other instruments of the Rosetta Plasma Consortium, and the ROSINA instrument made observations relevant to the generation of plasma waves in the cometary environment. Aims. Observations of plasma waves by the Rosetta Plasma Consortium Langmuir probe (RPC-LAP) can be explained by dispersion relations calculated based on measurements of ions by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA), and this gives insight into the relationship between plasma phenomena and the neutral coma, which is observed by the Comet Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument (ROSINA-COPS). Methods. We use the simple pole expansion technique to compute dispersion relations for waves on ion timescales based on the observed ion distribution functions. These dispersion relations are then compared to the waves that are observed. Data from the instruments RPC-LAP, RPC-ICA and the mutual impedance probe (RPC-MIP) are compared to find the best estimate of the plasma density. Results. We find that ion acoustic waves are present in the plasma at comet 67P/Churyumov-Gerasimenko, where the major ion species is H2O+. The bulk of the ion distribution is cold, kBTi = 0:01 eV when the ion acoustic waves are observed. At times when the neutral density is high, ions are heated through acceleration by the solar wind electric field and scattered in collisions with the neutrals. This process heats the ions to about 1 eV, which leads to significant damping of the ion acoustic waves. Conclusions. In conclusion, we show that ion acoustic waves appear in the H2O+ plasmas at comet 67P/Churyumov-Gerasimenko and how the interaction between the neutral and ion populations effects the wave properties. [ABSTRACT FROM AUTHOR]

Atira asteroids are recently-discovered celestial bodies characterised by orbits lying completely inside the heliocentric orbit of the Earth. The study of these objects is difficult due to the limitations of ground-based observations: objects can only be detected when the Sun is not in the field of view of the telescope. However, many asteroids are expected to exist in the inner region of the Solar System, many of which could pose a significant threat to our planet. In this paper, a small, low-cost, mission to visit the known Atira asteroids and to discover new Near Earth Asteroids (NEA) is proposed. The mission is realised using electric propulsion. The trajectory is optimised to maximise the number of visited asteroids of the Atira group using the minimum propellant consumption. During the tour of the Atira asteroids an opportunistic NEA discovery campaign is proposed to increase our knowledge of the asteroid population. The mission ends with a transfer to an orbit with perihelion equal to Venus’s orbit radius. This orbit represents a vantage point to monitor and detect asteroids in the inner part of the Solar System and provide early warning in the case of a potential impact. [ABSTRACT FROM AUTHOR]

The outbursts of comets, sudden large increases in their luminosity, are still very interesting and mysterious signs of activity of this celestial bodies. Most of the cometary outbursts are taking place at heliocentric distances where sublimation of water ice plays an important role in the activity of comets. However, the phenomenon is also observed far away from the Sun (i.e. ≃5-20 au) where the sublimation of water ice is negligible and the activity of comets is dominated by more volatile chemicals. Not only typical comets show 'cometary-like' activity but also Centaurs. In addition to the long-term changes in brightness related to heliocentric distances and short-periodic variations connected with the rotation of the nucleus, they also exhibit a random variations in luminosity which are similar to the cometary outbursts. Paper presents an overview of the most likely hypotheses and models which try to explain this phenomenon. [ABSTRACT FROM AUTHOR]

There is demonstrated how the unification in physics changes our point of view upon our cosmic home, the Solar System (SS) embedded in its Cosmic Hierarchy. Our entire Unified Physics can be defined with a single physical value, the mass of the proto-solar cosmic cloud. A direct consequence of this unified description is the idea of the Venus-centered SS challenging the Copernican heliocentric system. [ABSTRACT FROM AUTHOR]

The Secular influence of the change in the heliocentric gravitational constant on the evolution of orbits of Meteor Streams is examined by using the method of celestial mechanics with variable mass and variable gravitational constant. The change in the heliocentric gravitational constant includes the combined changes in the sun's mass and gravitational constant obtained from the modern observation of planets and spacecraft. The perturbation equations are solved by expanding series with mean anomaly. The solutions of the secular and periodic variation of orbital elements are derived. The theoretical results for the secular variables of the semi-major axes, solar distances at perihelion and orbital periods are given for three Meteor Streams: Dracorids, Quadrantids, and Ursids. The numerical results are shown in Table 2. The discussion and conclusion are drawn. [ABSTRACT FROM AUTHOR]

An analysis is presented for the photometric data on comet C/2013 A1 (Siding Spring) from observations at a large heliocentric distance (~4.1 AU). Comet C/2013 A1 (Siding Spring) displays intense activity despite the relatively large heliocentric distance. The morphology of the comet's coma is analyzed. The following parameters are measured: the color indices V-R, the normalized spectral gradient of the reflectivity of the comet's dust S', and the dust production rate Afρ. A numerical simulation is performed for the evolution of the comet's orbit after a close encounter with Mars. The most probable values are obtained for the Keplerian orbital elements of the comet over a hundred-year period. The comet's orbit remains nearly parabolic after passing the orbits of all the Solar System planets. [ABSTRACT FROM AUTHOR]

The basic structure of the Solar System is set by the presence of low-mass terrestrial planets in its inner part and giant planets in its outer part. This is the result of the formation of a system of multiple embryos with approximately the mass of Mars in the inner disk and of a few multi-Earth-mass cores in the outer disk, within the lifetime of the gaseous component of the protoplanetary disk. What was the origin of this dichotomy in the mass distribution of embryos/cores? We show in this paper that the classic processes of runaway and oligarchic growth from a disk of planetesimals cannot explain this dichotomy, even if the original surface density of solids increased at the snowline. Instead, the accretion of drifting pebbles by embryos and cores can explain the dichotomy, provided that some assumptions hold true. We propose that the mass-flow of pebbles is two-times lower and the characteristic size of the pebbles is approximately ten times smaller within the snowline than beyond the snowline (respectively at heliocentric distance r < r ice and r > r ice , where r ice is the snowline heliocentric distance), due to ice sublimation and the splitting of icy pebbles into a collection of chondrule-size silicate grains. In this case, objects of original sub-lunar mass would grow at drastically different rates in the two regions of the disk. Within the snowline these bodies would reach approximately the mass of Mars while beyond the snowline they would grow to ∼ 20 Earth masses. The results may change quantitatively with changes to the assumed parameters, but the establishment of a clear dichotomy in the mass distribution of protoplanets appears robust provided that there is enough turbulence in the disk to prevent the sedimentation of the silicate grains into a very thin layer. [ABSTRACT FROM AUTHOR]

We report the results of the long-term narrowband photometry and imaging monitoring of comet C/2012 F6 (Lemmon) with the robotic TRAPPIST telescope (La Silla Observatory). Observations covered 52 nights pre- and post-perihelion between December 11, 2012, and June 11, 2013 (perihelion: 24 March, 2013).We followed the evolution of the OH, NH, CN, C3, and C2 production rates computed with the Haser model as well as the evolution of the A(θ) f ρ parameter as a proxy for the dust production. All five gas species display similar slopes for the heliocentric dependence. An asymmetry about perihelion is observed, the rate of brightening being steeper than the rate of fading. The chemical composition of the comet's coma changes slightly along the orbit: the relative abundance of C2 to CN increases with the heliocentric distance (r) below -1.4 au and decreases with r beyond 1.4 au while the C3-to-CN ratio is constant during our observations. The behavior of the dust is different from that of the gas, the slope of the heliocentric dependence becoming steeper in early February, correlated to a change in the visual lightcurve slope. However, the dust color does not vary during the observations. The application of several enhancement techniques on the images revealed structures in the CN, C3, and C2 images. These features imply the existence of one or several active zone(s) on the comet nucleus. The shape of the structures is similar in these three filters and changes from a roughly hourglass shape in December and January to a corkscrew shape in February and March. The structures in the continuum filters (sampling the dust) are not correlated to those observed for the gas. During several full nights in February, we observed changes in the CN and C2 structures that repeated periodically because of the nucleus rotation, our derived rotational period being of 9.52 ± 0.05 h. [ABSTRACT FROM AUTHOR]

Measured in situ, the particle velocity distributions in the solar wind plasma reveal two distinct components: a Maxwellian (thermal) core, and a less dense but hotter suprathermal halo with a power-law distribution described by Lorentzian/Kappa distribution function. Despite this evidence, the existing attempts to parametrize anisotropic distributions and the resulting wave instabilities are limited to idealized models, which either ignore the suprathermal populations, or minimize the core, assuming it is cold. Here, a more realistic approach is identified, combining an isotropic Maxwellian core and an anisotropic bi-Kappa halo. This model is relevant at large heliocentric distances and for the slow winds, when the field-aligned strahl is less pronounced and kinetic energy densities in the core and halo are comparable. A comparative study with the cold-core-based model is performed on the electron whistler-cyclotron instability driven by the anisotropic halo. Derived exactly numerically, the instability thresholds and growth rates confirm the expectation that cyclotron instabilities are inhibited by the core thermal spread. This effect is enhanced by the increase of the halo-core relative density with heliocentric distance, suggesting that local conditions for this instability to develop at large radial distances in the solar wind are less favourable than predicted before. [ABSTRACT FROM AUTHOR]

An extension of the classical method by Alfano, for the analysis of optimal circle-to-circle two-dimensional orbit transfer, is presented for a deep space probe equipped with a solar electric primary propulsion system. The problem is formulated as a function of suitable design parameters, which allow the optimal transfer to be conveniently characterized in a parametric way, and an indirect approach is used to find the optimal steering law that minimizes the required propellant mass. The numerical results, obtained by solving a number of optimal control problems, are arranged into contour plots, characterized by different and well-defined behaviors depending on the value of the initial spacecraft propulsive acceleration, the final orbit radius, and the thruster’s specific impulse. The paper presents also a semi-analytical mathematical model for preliminary mission analysis purposes, which is shown to give excellent approximations of the (exact) numerical solutions when the number of revolutions of the spacecraft around the Sun is greater than five. An Earth–Mars cargo mission has been thoroughly investigated to validate the proposed approach. In this case, assuming a propulsion system with a specific impulse of 3000 s (comparable to that installed on the Deep Space 1 spacecraft), the results obtained with the semi-analytical model coincide, from an engineering point of view, with the numerical solutions both in terms of total mission time (about 8.3 years) and propellant mass fraction required (about 17.5%). By decreasing the value of the specific impulse, the differences between the results from the semi-analytical model and the numerical simulations tend to increase. However, good results are still possible if the number of revolutions of the spacecraft around the Sun is close to an integer number. [ABSTRACT FROM AUTHOR]

The history of the Copernicus controversy is reviewed, noting that it is far more complex than is often presented in the press or the popular literature. Copernicus's main problem was not the church but that the case for the heliocentric model lacked scientific evidence, and the Ptolemy model was then widely accepted. For this reason, much resistance existed to the heliocentric model from both the scientific and religious establishments. Actually, a significant source of Copernicus's support was from the church. This case is another example of the secular establishment oversimplifying, as well as occasionally distorting, history. The goal of this paper is to provide some light on this important historical event. [ABSTRACT FROM AUTHOR]

We explore the Triangulum–Andromeda (TriAnd) overdensity in the SPLASH (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo) and SEGUE (the Sloan Extension for Galactic Understanding and Exploration) spectroscopic surveys. Milky Way main-sequence turn-off stars in the SPLASH survey reveal that the TriAnd overdensity and the recently discovered Pan-Andromeda Archaeological Survey (PAndAS) stream share a common heliocentric distance (D ∼ 20 kpc), position on the sky, and line-of-sight velocity (VGSR ∼ 50 km s−1). Similarly, A-type, giant, and main-sequence turn-off stars selected from the SEGUE survey in the vicinity of the Segue 2 satellite show that TriAnd is prevalent in these fields, with a velocity and distance similar to Segue 2. The coincidence of the PAndAS stream and Segue 2 satellite in positional and velocity space to TriAnd suggests that these substructures are all associated, and may be a fossil record of group-infall on to the Milky Way halo. In this scenario, the Segue 2 satellite and PAndAS stream are ‘satellites of satellites’, and the large, metal-rich TriAnd overdensity is the remains of the group central. [ABSTRACT FROM AUTHOR]

Abstract: It has been argued that the decay rates of several radioactive nuclides are slightly lower at Earth’s aphelion than at perihelion, and that this effect might depend on heliocentric distance. It might then be expected that nuclear decay rates be considerably lower at larger distances from the sun, e.g., in the asteroid belt at 2–3AU from where most meteorites originate. If so, ages of meteorites obtained by analyses of radioactive nuclides and their stable daughter isotopes might be in error, since these ages are based on decay rates determined on Earth. Here we evaluate whether the large data base on nuclear cosmochronology offers any hint for discrepancies which might be due to radially variable decay rates. Chlorine-36 (t 1/2 =301,000 a) is produced in meteorites by interactions with cosmic rays and is the nuclide for which a decay rate dependence from heliocentric distance has been proposed, which, in principle, can be tested with our approach and the current data base. We show that compilations of 36Cl concentrations measured in meteorites offer no support for a spatially variable 36Cl decay rate. For very short-lived cosmic-ray produced radionuclides (half-lives<10–100days), the concentration should be different for meteorites hitting the Earth on the incoming vs. outgoing part of their orbit. However, the current data base of very short-lived radionuclides in freshly fallen meteorites is far from sufficient to deduce solid constraints. Constraints on the age of the Earth and the oldest meteorite phases obtained by the U–Pb dating technique give no hints for radially variable decay rates of the α-decaying nuclides 235U or 238U. Similarly, some of the oldest phases in meteorites have U–Pb ages whose differences agree almost perfectly with respective age differences obtained with “short-lived” radionuclides present in the early solar system, again indicating no variability of uranium decay rates in different meteorite parent bodies in the asteroid belt. Moreover, the oldest U–Pb ages of meteorites agree with the main-sequence age of the sun derived from helioseismology within the formal ∼1% uncertainty of the latter. Meteorite ages also provide no evidence for a decrease of decay rates with heliocentric distance for nuclides such as 87Rb (decay mode β −) 40K (β− and electron capture), and 147Sm (α). [Copyright &y& Elsevier]

It is well known that some Main Belt asteroids show comet-like features. A representative example is the first known Main Belt comet 133P/(7968) Elst-Pizarro. If the mechanisms causing this activity are too weak to develop visually evident comae or tails, the objects stay unnoticed. We are presenting a novel way to search for active asteroids, based on looking for objects with deviations from their expected brightnesses in a database. Just by using the MPCAT-OBS Observation Archive we have found five new candidate objects that possibly show a type of comet-like activity, and the already known Main Belt comet 133P/(7968) Elst-Pizarro. Four of the new candidates, (315) Constantia, (1026) Ingrid, (3646) Aduatiques, and (24 684) 1990 EU4, show brightness deviations independent of the object's heliocentric distance, while (35 101) 1991 PL16 shows deviations dependent on its heliocentric distance, which could be an indication of a thermal triggered mechanism. The method could be implemented in future sky survey programmes to detect outbursts on Main Belt objects almost simultaneously with their occurrence. [ABSTRACT FROM AUTHOR]

We analyzed the band splitting of a Type II radio burst observed on 1997 May 12 by ground- and space-based radio spectrometers. Type II radio emission is the most evident signature of coronal shock waves and the observed band splitting is generally interpreted as due to plasma emission from both upstream and downstream shock regions. From the inferred compression ratio we estimated, using the magnetohydrodynamic (MHD) Rankine-Hugoniot relations, the ambient Alfvén Mach number. By means of the electron density obtained by inverting white-light polarized brightness (pB) coronagraph data and the shock speed inferred from the Type II frequency drift, we finally derived a radial profile for the magnetic field strength in the middle corona. The result was compared with the field profile obtained in May 1997 (but above ∼5 R☉) with Faraday rotation measurements of extragalactic radio sources occulted by the corona. The power law of the form B(r) = 3.76 r-2.29 G inferred in that work nicely describes the combined set of data in a wide range of heliocentric distances (r ≈ 1.8-14 R☉). [ABSTRACT FROM AUTHOR]

An essay is presented concerning the mystical interpretation of the heliocentric universe espoused by medieval cosmology. Medieval astrology's perspective that Heaven was an extension of the material universe is presented. Theological depictions from the medieval period highlighting the relationship between the order of angels and the planets are also presented. An analysis of medieval works of art portraying mystical heliocentricity is also presented.

The article discusses the 1541 practica of German astrologer Andreas Aurifaber (1514-1559) and the public transmission of the heliocentric cosmology introduced by Renaissance astronomer Nicolas Copernicus. Practicas were primarily German-language quarto booklets issued annually during the early modern period which presented astrological predictions as well as astronomical predictions such as lunar and solar eclipses. The author explores Aurifaber's relationships with Austrian mathematician Georg Joachim Rheticus and German intellectual Philipp Melanchthon.

Determines the optical velocity for the Phoenix dwarf galaxy using Very Large Telescope observing program. Long-slit spectra of several members of the Phoenix dwarf galaxy; Heliocentric velocity of H[sub I] clouds.

This paper presents synthetic observations of long-lived coorbiting asteroids of Mercury, Venus, the Earth and Mars. Our sample is constructed by taking the limiting semimajor axes, differential longitudes and inclinations for long-lived stability provided by simulations. The intervals are randomly populated with values to create initial conditions. These orbits are re-simulated to check that they are stable and then re-sampled every 2.5 yr for 1 Myr. The Mercurian sample only contains horseshoe orbits, whereas the Martian sample only contains tadpoles. For both Venus and the Earth, the greatest concentration of objects on the sky occurs close to the classical Lagrange points at heliocentric ecliptic longitudes of 60° and 300°. The distributions are broad especially if horseshoes are present in the sample. The FWHM in heliocentric longitude for Venus is 325° and for the Earth is 328°. The mean and most common velocity of these coorbiting satellites coincides with the mean motion of the parent planet, but again the spread is wide with an FWHM of 27.8 and 21.0 arcsec h[sup -1] for Venus and the Earth, respectively. For Mars, the greatest concentration on the sky occurs at heliocentric ecliptic latitudes of ±12°. The peak of the velocity distribution occurs at 65 arcsec h[sup -1], significantly less than the Martian mean motion, while its FWHM is 32.3 arcsec h[sup -1]. The case of Mercury is the hardest of all, as the greatest concentrations occur at heliocentric longitudes of 16°.0 and 348°.5 and so are different from the classical values. The fluctuating eccentricity of Mercury means that these objects can have velocities exceeding 1000 arcsec h[sup -1] although the most common velocity is 459 arcsec h[sup -1], which is much less than the Mercurian mean motion. A variety of search strategies are discussed, including wide-field CCD imaging, space satellites such as the Global Astrometry Interferometer for Astrophysics (GAIA), ground-based surveys like the Sloan Digital Sky Survey (SDSS), as well as infrared cameras and space-borne coronagraphs. [ABSTRACT FROM AUTHOR]

The article offers a look on tracking the changing locations of planets. According to the author, the changing locations of the planets can be tracked in several ways through the use of various celestial coordinate systems. This system reveals the motion relative of the planet to the ecliptic, the apparent path the Sun follows during the year. Moreover, it is noted that the alternate system using heliocentric longitude has placed the viewer in an above the solar-system viewpoint, tracking the planets in their near-circular orbits around the Sun.