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We study different manifestations of the speed of light in theories of gravity where metric and connection are regarded as independent fields. We find that for a generic gravity theory in a frame with locally vanishing affine connection, the usual degeneracy between different manifestations of the speed of light is broken. In particular, the space-time causal structure constant () may become variable in that local frame. For theories of the form , this variation in has an impact on the definition of the luminosity distance (and distance modulus), which can be used to confront the predictions of particular models against Supernovae type Ia (SN Ia) data. We carry out this test for a quadratic gravity model without cosmological constant assuming (i) a constant speed of light and (ii) a varying speed of light (VSL), and find that the latter scenario is favored by the data. [ABSTRACT FROM AUTHOR]

We present a straightforward conceptual framework adapting the classical ideas introduced by Einstein and describe a realistic experiment to determine eventual anisotropics in the one-way speed of light independently of specific clock synchronization procedures. This establishes that we are not free to define either the one-way speed of light or time itself and must rely instead on further empirical observations to clarify these concepts, contrary to what was originally proposed in 1905. [ABSTRACT FROM AUTHOR]

Based on known analytic results, the thermal expectation value of the stress-energy tensor (SET) operator for the massless Dirac field is analysed from a hydrodynamic perspective. Key to this analysis is the Landau decomposition of the SET, with the aid of which we find terms which are not present in the ideal SET predicted by kinetic theory. Moreover, the quantum corrections become dominant in the vicinity of the speed of light surface (SOL). While rigidly-rotating thermal states cannot be constructed for the Klein–Gordon field, we perform a similar analysis at the level of quantum corrections previously reported in the literature and we show that the Landau frame is well-defined only when the system is enclosed inside a boundary located inside or on the SOL. We discuss the relevance of these results for accretion disks around rapidly-rotating pulsars. [ABSTRACT FROM AUTHOR]

We present the results of the χ2 minimization model fitting technique applied to optical and near-infrared photometric and radial velocity data for a sample of nine fundamental and three first overtone classical Cepheids in the Small Magellanic Cloud (SMC). The near-infrared photometry (JK filters) was obtained by the European Southern Observatory (ESO) public survey 'VISTA near-infrared Y, J, Ks survey of the Magellanic Clouds system' (VMC). For each pulsator, isoperiodic model sequences have been computed by adopting a nonlinear convective hydrodynamical code in order to reproduce the multifilter light and (when available) radial velocity curve amplitudes and morphological details. The inferred individual distances provide an intrinsic mean value for the SMC distance modulus of 19.01 mag and a standard deviation of 0.08mag, in agreement with the literature. Moreover, the intrinsic masses and luminosities of the best-fitting model show that all these pulsators are brighter than the canonical evolutionary mass-luminosity relation (MLR), suggesting a significant efficiency of core overshooting and/or mass-loss. Assuming that the inferred deviation from the canonical MLR is only due to mass-loss, we derive the expected distribution of percentage mass-loss as a function of both the pulsation period and the canonical stellar mass. Finally, a good agreement is found between the predicted mean radii and current period-radius (PR) relations in the SMC available in the literature. The results of this investigation support the predictive capabilities of the adopted theoretical scenario and pave the way for the application to other extensive data bases at various chemical compositions, including the VMC Large Magellanic Cloud pulsators and Galactic Cepheids with Gaia parallaxes. [ABSTRACT FROM AUTHOR]

This article discusses an early example of interferometric, experimental research related to Einstein's Special Theory of Relativity. This research concerned two series of experiments on the velocity of light in moving media, conducted between 1914 and 1921 by the Amsterdam physicist Pieter Zeeman. With the first of these series, on the velocity of light in moving water, Zeeman obtained an important result that validated the so called ‘dispersion term' of the formula for the velocity of light in moving media. Less clear is the scientific objective of the second series, in which Zeeman measured the velocity of light in moving solid media. It seems that Zeeman's interest in this second series was triggered mainly by the technical challenges posed by these experiments. In this way, they reveal the increasing tendency of Zeeman's later research to be led by technical and experimental challenges, rather than by the actual scientific developments. [ABSTRACT FROM AUTHOR]

We present the Galaxy And Mass Assembly (GAMA) Panchromatic Data Release (PDR) constituting over 230 deg2 of imaging with photometry in 21 bands extending from the far- UV to the far-IR. These data complement our spectroscopic campaign of over 300k galaxies, and are compiled from observations with a variety of facilities including: GALaxy Evolution eXplorer, Sloan Digital Sky Survey, Visible and Infrared Telescope for Astronomy (VISTA), Wide-field Infrared Survey Explorer, and Herschel, with the GAMA regions currently being surveyed byVLT Survey Telescope (VST) and scheduled for observations by Australian Square Kilometer Array Pathfinder (ASKAP). These data are processed to a common astrometric solution, from which photometry is derived for ∼221 373 galaxies with r < 19.8 mag. Online tools are provided to access and download data cutouts, or the full mosaics of the GAMA regions in each band. We focus, in particular, on the reduction and analysis of the VISTA VIsta Kilo-degree INfrared Galaxy data, and compare to earlier data sets (i.e. 2MASS and UKIDSS) before combining the data and examining its integrity. Having derived the 21-band photometric catalogue, we proceed tofit the data using the energy balance code MAGPHYS. These measurements are then used to obtain the first fully empirical measurement of the 0.1-500 μm energy output of the Universe. Exploring the cosmic spectral energy distribution across three time-intervals (0.3-1.1, 1.1-1.8, and 1.8-2.4 Gyr), we find that the Universe is currently generating (1.5 ± 0.3) × 1035 h70 WMpc-3, down from (2.5 ± 0.2) × 1035 h70 W Mpc-3 2.3 Gyr ago. More importantly, we identify significant and smooth evolution in the integrated photon escape fraction at all wavelengths, with the UV escape fraction increasing from 27(18) per cent at z = 0.18 in NUV(FUV) to 34(23) per cent at z = 0.06. [ABSTRACT FROM AUTHOR]

In this paper, the Selleri transformations along with the light speed predictions of "equivalent" space-time transformations, clock synchronization, and one-way light speed measurement are discussed. First, using a one-way light speed calculation, it is reaffirmed that the Selleri transformations are not equivalent to any in the set of "equivalent" transformations developed by Selleri (which includes the Lorentz transformations). They stand alone as the only transformations that accord with light speed observation and for which the condition of absolute simultaneity is satisfied. Second, it is shown that one-way light speed can and has been measured despite claims suggesting otherwise since synchronized clocks associated with the highly successful GPS are available for this measurement. Third, a new one-way light speed test is described that does not require clock synchronization of any kind. This is contrary to the popular belief that one-way light speed cannot be measured independently of a convention on clock synchronization. [ABSTRACT FROM AUTHOR]

Context. Two classes of gamma-ray bursts (GRBs), short and long, have been determined without any doubts, and are usually prescribed to different physical scenarios. A third class, intermediate in T90 durations has been reported in the datasets of BATSE, Swift, RHESSI, and possibly BeppoSAX. The latest release of >1500 GRBs observed by Fermi gives an opportunity to further investigate the duration distribution. Aims. The aim of this paper is to investigate whether a third class is present in the log T90 distribution, or whether it is described by a bimodal distribution. Methods. A standard χ² fitting of a mixture of Gaussians was applied to 25 histograms with different binnings. Results. Different binnings give various values of the fitting parameters, as well as the shape of the fitted curve. Among five statistically significant fits, none is trimodal. Conclusions. Locations of the Gaussian components are in agreement with previous works. However, a trimodal distribution, understood in the sense of having three distinct peaks, is not found for any binning. It is concluded that the duration distribution in the Fermi data is well described by a mixture of three log-normal distributions, but it is intrinsically bimodal, hence no third class is present in the T90 data of Fermi. It is suggested that the log-normal fit may not be an adequate model. [ABSTRACT FROM AUTHOR]

Aims. We describe a new algorithm for extracting photometric information from meteor images. Methods. The time history of a moving point source of variable brightness is explicitly deconvolved from the spatial distribution of the meteor signal on the image. The method can be applied to time-integrated meteor images if kinematic information is independently available or, alternatively, assumed. Formal uncertainty estimation and reporting is included. Results. We test the algorithm on synthetic meteor images and meteors recorded during a recent double-station meteor observing campaign in Greece. In the first case, we find that both the synthetic signal and the a priori time variation of the flux are faithfully reproduced. In the second, the fluxes obtained from the two stations agree to ~20%. [ABSTRACT FROM AUTHOR]

Many authors noted that the principle of relativity together with space–time homogeneity and isotropy restricts the form of the coordinate transformations from one inertial frame to another to being Lorentz-like. The equations contain a free parameter, k (equal to c −2 in special relativity), whose value is claimed to be merely an empirical matter, so that special relativity does not need the postulate of constancy of the speed of light. I analyze this claim and argue that the distinction between the cases k =0 and k ≠ 0 is on the level of a postulate and that until we assume one or the other, we have an incomplete structure that leaves many fundamental questions undecided, including basic prerequisites of experimentation. I examine an analogous case in which isotropy is the postulate dropped and use it to illustrate the problem. Finally I analyze two attempts by Sfarti, and Behera and Mukhopadhyay to derive the constancy of the speed of light from the principle of relativity. I show that these attempts make hidden assumptions that are equivalent to the second postulate. [ABSTRACT FROM AUTHOR]

We present a photometric and spectroscopic study of the polar ring galaxy A0136-0801 in order to constrain its formation history. Near-infrared and optical imaging data are used to extract surface brightness and colour profiles of the host galaxy and the wide polar structure in A0136-0801. The host galaxy dominates the light emission in all bands; the polar structure is more luminous in the optical bands and is three times more extended than the main spheroid. The average stellar population in the spheroid is redder than in the polar structure and we use their (B - K) versus (J - K) colours to constraint the ages of these populations using stellar population synthesis models. The inferred ages are 3-5 Gyr for the spheroid and 1-3 Gyr for the polar structure. We then use long slit spectra along the major axis of the polar structure to derive the emission line ratios and constrain the oxygen abundance, metallicity and star formation rate in this component. We find 12 + log(O/H) = 8.33 ± 0.43 and Z ~ 0.32 Z⊙, using emission line ratios. These values are used, together with the ratio of the baryonic masses of the host galaxy and polar structure, to constrain the possible models for the formation scenario. We conclude that the tidal accretion of gas from a gas-rich donor or the disruption of a gas-rich satellite are formation mechanisms that may lead to systems with physical parameters in agreement with those measured for A0136-0801. [ABSTRACT FROM AUTHOR]

The electromagnetic field equations are solved to give the 4-potential in Hermite-Gaussian beams as a function of both the 4-positions of the beam waist and each point in the field. These solutions are the sums of products of position-dependent complex 4-vectors and modified Bateman- Hillion functions. It is assumed that the time difference between the beam waist and each other point is equal to the distance between the points divided by the speed of light. This method is shown to generate solutions that preserve their forms under Lorentz transformations that also correspond to the well known paraxial solutions for the case of nearly parallel beams. [ABSTRACT FROM AUTHOR]

We consider the possibility that the Gaia mission can supply data which will improve the photometric calibration of LSST. After outlining the LSST calibration process and the information that will be available from Gaia, we explore two options for using Gaia data. The first is to use Gaia G-band photometry of selected stars, in conjunction with knowledge of the stellar parameters Teff, log g, and Av, and in some cases Z, to create photometric standards in the LSST u, g, r, i, z, and y bands. We consider both main sequence (MS) stars and DA white dwarfs (WD). The accuracies of the resulting standard magnitudes from MS stars are found to be insufficient to satisfy LSST requirements using Gaia data alone, but with the potential to do so when supplemented with groundbased spectroscopy. The accuracies of the WD derived standards are generally adequate, but also require groundbased spectroscopy. The second option is combine the LSST bandpasses into a synthetic Gaia G band, which is a close approximation to the real Gaia G band. This allows synthetic Gaia G photometry to be directly compared with actual Gaia G photometry at a level of accuracy which is useful for both verifying and improving LSST photometric calibration. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the accuracy of the C constant for ray tracing–assisted intraocular lens (IOL) power calculation. Design: Case series. Setting: Public university hospital and private clinic. Methods: Preoperatively, all intraocular distances were measured using laser biometry. Various IOL designs were studied; powers ranged from −5.0 diopters (D) to +38.0 D. The IOL power calculation was performed with the Olsen formula using the C constant and compared with the Haigis, Hoffer Q, Holladay 1, and the SRK/T formulas on optimized datasets. Outcome measures were the error of the prediction, expressed as the arithmetic error, and the absolute error between the observed refraction and the predicted refraction. Results: Two thousand forty-three cases from the 2 centers were studied. No significant differences were found between the Haigis, Hoffer Q, Holladay 1, and SRK/T formulas with the exception of the SRK/T formula, which performed better than the other thin-lens formulas in eyes with an axial length (AL) greater than 27.0 mm (P<.01). Compared with the SRK/T formula, the Olsen formula showed an improvement of 15% and 14% in the mean absolute error and a 39% and 85% reduction in the number of large errors (>1.0 D) for the 2 series, respectively (P<.0001). Contrary to the Olsen formula, all thin-lens formulas showed a significant bias in terms of the AL, keratometry reading, and anterior segment length (P<.0001). Conclusion: The C constant is a promising concept for ray tracing–assisted IOL power calculation. Financial Disclosure: Dr. Olsen is a shareholder of IOL Innovations Aps, manufacturer of the Phacooptics IOL calculation software. Dr. Hoffmann has no financial or proprietary interest in any material or method mentioned. [Copyright &y& Elsevier]

The ionosphere is the main error source in GNSS measurements and in extreme cases can degrade the positioning significantly, with errors exceeding 100 m; therefore, modelling and predicting of this type of error is crucial and critical. The ionospheric effect can be reduced using different techniques, such as dual-frequency receiver or suitable augmentation system (DGPS, SBAS); the aforesaid approaches involve the use of expensive devices and/or complex architectures. Single frequency stand-alone receivers are the cheapest and most widespread GNSS devices; they can estimate and partially correct the error due to the ionosphere, through adequate algorithms, which use parameters broadcasted by the navigation message. The aim of this paper is performance assessment of the ionospheric model NeQuick, adopted by the European GNSS Galileo for single frequency receivers. The analysis is performed in measurements domain and the data are collected in different geographical locations and in various geomagnetic conditions. [ABSTRACT FROM AUTHOR]

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An introduction to the journal is presented in which the author discusses research articles within this issue which focus on topics including the socio-historical approach to determining the speed of light, the politicization of science, and the hermeneutic circle.

We discuss how light acquired a velocity through history, from the ancient Greeks to the early modern era. Combining abstract debates, models of light, practical needs, planned research and chance, this history illustrates several key points that should be brought out in science education. [ABSTRACT FROM AUTHOR]

The Gaia spectro-photometric data consist of white-light G magnitudes from unfiltered fluxes measured in the astrometric field CCDs, and low resolution prism spectra measured in the blue (BP) and red (RP) CCDs. The integrated flux of these BP and RP spectra will yield GBP and GRP magnitudes as two broad passbands. The internal flux calibration will correct for all possible instrumental effects and produce mean spectral energy distributions in an internally defined flux scale. The purpose of the absolute flux calibration is to tie this flux scale to physical units by means of spectro-photometric standard stars that rely ultimately on Vega's absolute flux scale. The characteristics of the Gaia spectrophotometric system will be described, and the absolute calibration process will be outlined and compared with examples of classical systems. [ABSTRACT FROM AUTHOR]

The speed of light in vacuum, one of the most important and precisely measured natural constants, is fixed by convention to m . Advanced theories predict possible deviations from this universal value, or even quantum fluctuations of c. Combining arguments from quantum parameter estimation theory and classical general relativity, we here establish rigorously the existence of lower bounds on the uncertainty to which the speed of light in vacuum can be determined in a given region of space-time, subject to several reasonable restrictions. They provide a novel perspective on the experimental falsifiability of predictions for the quantum fluctuations of space-time. [ABSTRACT FROM AUTHOR]

The speed of light is commonly known as c  =  300 000 km s−1. But rarely people have in mind that this value is only for vacuum conditions. Using a laser distance meter we can calculate the speed of light in different transparent materials. [ABSTRACT FROM AUTHOR]

I show that the reduced speed of light (RSL) approximation, when used properly (i.e., as originally designed—only for local sources but not for the cosmic background), remains a highly accurate numerical method for modeling cosmic reionization. Simulated ionization and star formation histories from the “Cosmic Reionization on Computers” project are insensitive to the adopted value of the RSL for as long as that value does not fall below about 10% of the true speed of light. A recent claim of the failure of the RSL approximation in the Illustris reionization model appears to be due to the effective speed of light being reduced in the equation for the cosmic background too and hence illustrates the importance of maintaining the correct speed of light in modeling the cosmic background. [ABSTRACT FROM AUTHOR]

The article discusses the use of laser distance meter to determine the refractive indices by measuring speed of light in transparent media. Topics discussed include aspects of the time-of-flight measurements in which pulses are emitted by lasers, use of the meters in construction and home improvement projects, robotics and military applications, and use of the meters in determining the optical properties of transparent solids.

Reconstructing the shape of an object from images is an important problem in computer vision that has led to a variety of solution strategies. This survey covers photometric stereo, i.e., techniques that exploit the observed intensity variations caused by illumination changes to recover the orientation of the surface. In the most basic setting, a diffuse surface is illuminated from at least three directions and captured with a static camera. Under some conditions, this allows to recover per-pixel surface normals. Modern approaches generalize photometric stereo in various ways, e.g., relaxing constraints on lighting, surface reflectance and camera placement or creating different types of local surface estimates. Starting with an introduction for readers unfamiliar with the subject, we discuss the foundations of this field of research. We then summarize important trends and developments that emerged in the last three decades. We put a focus on approaches with the potential to be applied in a broad range of scenarios. This implies, e.g., simple capture setups, relaxed model assumptions, and increased robustness requirements. The goal of this review is to provide an overview of the diverse concepts and ideas on the way towards more general techniques than traditional photometric stereo. [ABSTRACT FROM AUTHOR]

Measurements of the speed of light have been carried out in the past by the correlation between gamma rays detected in two scintillation detectors. To demonstrate that the speed of gamma rays in a transparent medium is very close to that observed in the vacuum, a time-of-flight experiment was organized in an educational context with undergraduate students, making use of two BaF2 detectors and a small intensity 22Na source. Measurements of time-of-flight spectra were carried out for several values of the distance between the two detectors, allowing us to extract the speed of photons in air. A measurement was also done with an amount of water along the photon path and the result compared with that obtained in air. Various experimental aspects of the interaction of gammas with the detectors were finally addressed through GEANT simulations of the setup to interpret the results. [ABSTRACT FROM AUTHOR]