Showing papers on "Sky published in 2006"

Retrieving Cloud Characteristics from Ground-Based Daytime Color All-Sky Images

Abstract: A discussion is presented of daytime sky imaging and techniques that may be applied to the analysis of full-color sky images to infer cloud macrophysical properties. Descriptions of two different types of skyimaging systems developed by the authors are presented, one of which has been developed into a commercially available instrument. Retrievals of fractional sky cover from automated processing methods are compared to human retrievals, both from direct observations and visual analyses of sky images. Although some uncertainty exists in fractional sky cover retrievals from sky images, this uncertainty is no greater than that attached to human observations for the commercially available sky-imager retrievals. Thus, the application of automatic digital image processing techniques on sky images is a useful method to complement, or even replace, traditional human observations of sky cover and, potentially, cloud type. Additionally, the possibilities for inferring other cloud parameters such as cloud brokenness and solar obstruction further enhance the usefulness of sky imagers.

Detection of a 63° Cold Stellar Stream in the Sloan Digital Sky Survey

Abstract: We report on the detection in Sloan Digital Sky Survey data of a 63°-long tidal stream of stars, extending from Ursa Major to Cancer The stream has no obvious association with the orbit of any known cluster or galaxy The contrast of the detected stream is greatest when using a star count filter that is matched to the color-magnitude distribution of stars in M13, which suggests that the stars making up the stream are old and metal-poor The visible portion of the stream is very narrow and about 85 kpc above the Galactic disk, suggesting that the progenitor is or was a globular cluster While the surface density of the stream varies considerably along its length, its path on the sky is very smooth and uniform, showing no evidence of perturbations by large mass concentrations in the nearby halo While definitive constraints cannot be established without radial velocity information, the stream's projected path and estimates of its distance suggest that we are observing the stream near the perigalacticon of its orbit

Detection of a 63 Degree Cold Stellar Stream in the Sloan Digital Sky Survey

Abstract: We report on the detection in Sloan Digital Sky Survey data of a 63 degree-long tidal stream of stars, extending from Ursa Major to Cancer. The stream has no obvious association with the orbit of any known cluster or galaxy. The contrast of the detected stream is greatest when using a star count filter that is matched to the color-magnitude distribution of stars in M 13, which suggests that the stars making up the stream are old and metal poor. The visible portion of the stream is very narrow and about 8.5 kpc above the Galactic disk, suggesting that the progenitor is or was a globular cluster. While the surface density of the stream varies considerably along its length, its path on the sky is very smooth and uniform, showing no evidence of perturbations by large mass concentrations in the nearby halo. While definitive constraints cannot be established without velocity information, the stream's projected path and estimates of its distance suggest that we are observing the stream near the perigalacticon of its orbit.

Low-Mass Dwarf Template Spectra from the Sloan Digital Sky Survey

Abstract: We present template spectra of low-mass (M0-L0) dwarfs derived from over 4,000 Sloan Digital Sky Survey (SDSS) spectra. These composite spectra are suitable for use as medium-resolution (R ~ 1,800) radial velocity standards. We report mean spectral properties (molecular bandhead strengths,equivalent widths) and use the templates to investigate the effects of magnetic activity and metallicity on the spectroscopic and photometric properties of low-mass stars.

What aspects of galaxy environment matter

Abstract: We determine what aspects of the density field surrounding galaxies most affect their properties. For Sloan Digital Sky Survey galaxies, we measure the group environment, meaning the host group luminosity and the distance from the group center (hereafter, ``groupocentric distance''). For comparison, we measure the surrounding density field on scales ranging from 100 kpc/h to 10 Mpc/h. We use the relationship between color and group environment to test the null hypothesis that only the group environment matters, searching for a residual dependence of properties on the surrounding density. Generally, red galaxies are slightly more clustered on small scales (about 100--300 kpc/h) than the null hypothesis predicts, possibly indicating that substructure within groups has some importance. At large scales (> 1 Mpc/h), the actual projected correlation functions of galaxies are biased at less than the 5% level with respect to the null hypothesis predictions. We exclude strongly the converse null hypothesis, that only the surrounding density (on any scale) matters. These results generally encourage the use of the halo model description of galaxy bias, which models the galaxy distribution as a function of host halo mass alone. We compare these results to proposed galaxy formation scenarios within the Cold Dark Matter cosmological model.

A 22° tidal tail for palomar 5

Abstract: Using Data Release 4 of the Sloan Digital Sky Survey, we have applied an optimal-contrast, matched-filter technique to trace the trailing tidal tail of the globular cluster Palomar 5 to a distance of 185 from the center of the cluster This more than doubles the total known length of the tail to some 22° on the sky Based on a simple model of the Galaxy, we find that the stream's orientation on the sky is consistent at the 17 σ level with existing proper-motion measurements We find that a spherical Galactic halo is adequate to model the stream over its currently known length, and we are able to place new constraints on the current space motion of the cluster

ICESat Antarctic elevation data: Preliminary precision and accuracy assessment

Abstract: [1] Since ‘first light’ on February 20th, 2003, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) has derived surface elevations from ∼86°N to 86°S latitude. These unique altimetry data have been acquired in a series of observation periods in repeated track patterns using all three Geoscience Laser Altimeter System (GLAS) lasers. Here, we focus on Antarctic ice sheet elevation data that were obtained in 2003–2004. We present preliminary precision and accuracy assessments of selected elevation data, and discuss factors impacting elevation change detection. We show that for low slope and clear sky conditions, the precision of GLA12 Laser 2a, Release 21 data is ∼2.1 cm and the relative accuracy of ICESat elevations is ±14 cm based on crossover differences.

Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Beam Profiles, Data Processing, Radiometer Characterization and Systematic Error Limits

Abstract: The WMAP satellite has completed 3 years of observations of the cosmic microwave background radiation. The 3-year data products include several sets of full sky maps of the Stokes I, Q and U parameters in 5 frequency bands, spanning 23 to 94 GHz, and supporting items, such as beam window functions and noise covariance matrices. The processing used to produce the current sky maps and supporting products represents a significant advancement over the first year analysis, and is described herein. Improvements to the pointing reconstruction, radiometer gain modeling, window function determination and radiometer spectral noise parametrization are presented. A detailed description of the updated data processing that produces maximum likelihood sky map estimates is presented, along with the methods used to produce reduced resolution maps and corresponding noise covariance matrices. Finally two methods used to evaluate the noise of the full resolution sky maps are presented along with several representative year-to-year null tests, demonstrating that sky maps produced from data from different observational epochs are consistent.

A 22 Degree Tidal Tail for Palomar 5

Abstract: Using Data Release 4 of the Sloan Digital Sky Survey, we have applied an optimal contrast, matched filter technique to trace the trailing tidal tail of the globular cluster Palomar 5 to a distance of 18.5 degrees from the center of the cluster. This more than doubles the total known length of the tail to some 22 degrees on the sky. Based on a simple model of the Galaxy, we find that the stream's orientation on the sky is consistent at the 1.7 sigma level with existing proper motion measurements. We find that a spherical Galactic halo is adequate to model the stream over its currently known length, and we are able to place new constraints on the current space motion of the cluster.

A Catalog of Spectroscopically Selected Close Binary Systems from the Sloan Digital Sky Survey Data Release Four

Abstract: We present a spectroscopic sample of 747 detached close binary systems from the Sloan Digital Sky Survey (SDSS) Fourth Data Release. The majority of these binaries consist of a white dwarf primary and a low-mass secondary (typically M dwarf) companion. We have determined the temperature and gravity for 496 of the white dwarf primaries and the spectral type and magnetic activity properties for 661 of the low-mass secondaries. We have estimated the distances for each of the white dwarf-main-sequence star binaries and use white dwarf evolutionary grids to establish the age of each binary system from the white dwarf cooling times. With respect to a spectroscopically identified sample of ~8000 isolated M dwarf stars in the SDSS, the M dwarf secondaries show enhanced activity with a higher active fraction at a given spectral type. The white dwarf temperatures and gravities are similar to the distribution of ~1900 DA white dwarfs from the SDSS. The ages of the binaries in this study range from ~0.5 Myr to nearly 3 Gyr (average age ~0.20 Gyr).

Estimation of fractional sky cover from broadband shortwave radiometer measurements

Abstract: [1] We outline a methodology for estimating fractional sky cover for an effective 160° field of view from an analysis of surface measurements of downwelling total and diffuse shortwave (SW) irradiance. The data are screened for optically thicker overcast cases, after which an empirically derived formulation is used to estimate the fractional sky cover for the remaining data. The retrieved fractional sky cover time series is then evaluated to mitigate times of anomalous behavior caused by the thick overcast screening. The resultant sky cover estimates show a high degree of repeatability given nominally well maintained and operated radiometer systems and the use of the Long and Ackerman (2000) methodology for estimating the clear-sky total and diffuse SW. Thus the resultant fractional sky-cover estimates appear to be fairly independent of the particular climate regime and model of radiometers used, at least for the climate regimes we have tested so far. The sky-cover estimates agree to better than 10% root mean square sky cover amount with sky imager retrievals and human observations, which is as good as the agreement between sky imaging systems and observers themselves. As such, this methodology becomes a powerful tool for satellite and model validations and climatological analyses including the study of trends in cloud amount. Analysis shows that the technique also produces realistic frequency distributions, showing that the continental midlatitude regimes included in the study are typified by clear-sky occurring about 1/3 of the time, overcast about 1/3 of the time, and partly cloudy skies to varying extent occurring the remaining 1/3 of the time. By contrast, the tropical western Pacific oceanic regime during the Nauru99 field experiment exhibits far more frequent occurrence of partly cloudy skies, with sky cover amounts of 20% to 50% occurring about half the time.

Celestial polarization patterns during twilight.

Abstract: Scattering of sunlight produces patterns of partially linearly polarized light in the sky throughout the day, and similar patterns appear at night when the Moon is bright. We studied celestial polarization patterns during the period of twilight, when the Sun is below the horizon, determining the degree and orientation of the polarized-light field and its changes before sunrise and after sunset. During twilight, celestial polarized light occurs in a wide band stretching perpendicular to the location of the hidden Sun and reaching typical degrees of polarization near 80% at wavelengths >600 nm. In the tropics, this pattern appears ∼1 h before local sunrise or disappears ∼1 h after local sunset (within 10 min⁡ after the onset of astronomical twilight at dawn, or before its end at dusk) and extends with little change through the entire twilight period.

A Catalog of 1022 Bright Contact Binary Stars

Abstract: In this work we describe a large new sample of contact binary stars extracted in a uniform manner from sky patrol data taken by the ROTSE-I telescope. Extensive ROTSE-I light-curve data are combined with J-, H-, and K-band near-infrared data taken from the Two Micron All Sky Survey to add color information. Contact binary candidates are selected using the observed period-color relation. Candidates are confirmed by visual examination of the light curves. To enhance the utility of this catalog, we derive a new J - H period-color-luminosity relation and use this to estimate distances for the entire catalog. From these distance estimates we derive an estimated contact binary space density of × 10-5 pc-3.

Biomarkers in disk-averaged near-UV to near-IR Earth spectra using Earthshine observations ⋆

Abstract: We analyse the detectability of vegetation on a global scale on Earth's surface. Considering its specific reflectance spectrum showing a sharp edge around 700 nm, vegetation can be considered as a potential global biomarker. This work, based on observational data, aims to characterise and to quantify this signature in the disk-averaged Earth's spectrum. Earthshine spectra have been used to test the detectability of the "Vegetation Red Edge" (VRE) in the Earth spectrum. We obtained reflectance spectra from near UV (320 nm) to near IR (1020 nm) for different Earth phases (continents or oceans seen from the Moon) with EMMI on the NTT at ESO/La Silla, Chile. We accurately correct the sky background and take into account the phase-dependent colour of the Moon. VRE measurements require a correction of the ozone Chappuis absorption band and Rayleigh plus aerosol scattering. Results : The near-UV spectrum shows a dark Earth below 350 nm due to the ozone absorption. The Vegetation Red Edge is observed when forests are present ($4.0\%$ for Africa and Europe), and is lower when clouds and oceans are mainly visible ($1.3\%$ for the Pacific Ocean). Errors are typically $\pm0.5$, and $\pm1.5$ in the worst case. We discuss the different sources of errors and bias and suggest possible improvements. We showed that measuring the VRE or an analog on an Earth-like planet remains very difficult (photometric relative accuracy of 1\% or better). It remains a small feature compared to atmospheric absorption lines. A direct monitoring from space of the global (disk-averaged) Earth's spectrum would provide the best VRE follow-up.

Enhanced GNSS signal processing

Abstract: In accordance with embodiments of the invention, a skyward-looking sensor enables classification of points in its hemispherical field of view as either sky, partial sky or not sky, which in turn enables determination from data supplied by the GNSS receiver of whether each satellite in the GNSS antenna's field of view is in a region of sky, partial sky or not sky. Pseudrange and phase data from GNSS satellites determined to be in a region of sky can be considered reliable and used with confidence in a positioning solution. Pseudrange and phase data from GNSS satellites determined to be in a region of partial sky can be considered suspect and can therefore only contribute to a position solution with limited confidence and decreased accuracy. Pseudorange and phase data from GNSS satellites determined to be in a region of no sky can be considered unreliable and excluded from use in a positioning solution.

A review of optical sky brightness and extinction at dome c, antarctica

Abstract: The recent discovery of exceptional seeing conditions at Dome C, Antarctica, raises the possibility of constructing an optical observatory there with unique capabilities. However, little is known from an astronomer's perspective about the optical sky brightness and extinction at Antarctic sites. We review the contributions to sky brightness at high-latitude sites and calculate the amount of usable dark time at Dome C. We also explore the implications of the limited sky coverage of high-latitude sites and review optical extinction data from the South Pole. Finally, we examine the proposal of Baldry & Bland-Hawthorn to extend the amount of usable dark time through the use of polarizing filters.

Clio: a 3-5 micron AO planet-finding camera

Abstract: Clio is an adaptive-optics camera mounted on the 6.5 meter MMT optimized for diffraction-limited L' and M-band imaging over a ~ 15" field. The instrument was designed from the ground up with a large well-depth, fast readout thermal infrared (~ 3_5μ m) 320 by 256 pixel InSb detector, cooled optics, and associated focal plane and pupil masks (with the option for a coronograph) to minimize the thermal background and maximize throughput. When coupled with the MMT's adaptive secondary AO (two warm reflections) system's low thermal background, this instrument is in a unique position to image nearby warm planets, which are the brightest in the L' and M-band atmospheric windows. We present the current status of this recently commissioned instrument that performed exceptionally during first light. Our instrument sensitivities are impressive and are sky background limited: for an hour of integration, we obtain an L'-band 5 σ detection limit of of 17.0 magnitudes ~ 80%) and an M-band limit of 14.5 (Strehl ~ 90%). Our M-band sensitivity is lower due to the increase in thermal sky background. These sensitivities translate to finding relatively young planets five times Jupiter mass (MJup ) at 10 pc within a few AU of a star. Presently, a large Clio survey of nearby stellar systems is underway including a search for planets around solar-type stars, M dwarfs, and white dwarfs. Even with a null result, we can place strong constraints on planet distribution models.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Solar photovoltaic power generation system

Abstract: PROBLEM TO BE SOLVED: To provide a solar photovoltaic power generation system which can observe clouds which influence solar photovoltaic power generation over the sky, and also can accurately predict a distribution of clouds at any time in the future and thereby can predict a change in power to be generated in advance. SOLUTION: The solar photovoltaic power generation system comprises a solar light panel which receives solar light and generates power; a 360° camera which images the whole sky at a point where the solar light panel is installed; an image processor which detects the distribution and movement of clouds from the image of the whole sky; and a power predicter which predicts a distribution of clouds at a predetermined point in the future according to the detected distribution and movement of clouds, and then predicts the power to be generated by the solar light panel at the predetermined point in the future based on the predicted distribution of clouds. COPYRIGHT: (C)2007,JPO&INPIT

Average daylight factor for the 15 CIE standard skies

Abstract: For daylighting calculations, the design criteria are often expressed in terms of average daylight factors (DFave) with the computations being based on the CIE (International Commission on Illumination) overcast sky, which is generally considered to provide the worst daylight condition. The daylight illuminance of a room is mainly influenced by the luminances and patterns of the sky in the direction of view of the window at any given time. Overcast skies may not always be the appropriate reference sky types for daylighting analysis. Recently, Kittler et al. have proposed a new range of 15 standard sky luminance distributions including five clear, five partly cloudy and five overcast sky types. These 15 sky luminance models have been adopted as the CIE General Standard Skies. This paper presents an approach to computing the DFave for the 15 standard skies. The techniques for calculating the two configuration parameters for the DFave determination, namely; (a) light received directly from the sky above the ...

Spectral radiance and sky luminance in Antarctica: a case study

Abstract: Sky luminance and spectral radiance has been characterised at Neumayer, Antarctica for selected situations during the austral summer 2003/04. Luminance has also been measured at Boulder, Colorado, USA in June 2003. The high reflectivity of the surface (albedo) in Antarctica, reaching values up to 100% in the ultraviolet (UV) and visible part of the solar spectrum due to snow cover, modifies the radiation field considerably when compared to mid-latitudes. A dependence of luminance and spectral radiance on solar zenith angle (SZA) and surface albedo has been identified. For snow and cloudless sky, the horizon luminance exceeds the zenith luminance by as much as a factor of 8.2 and 7.6 for a SZA of 86° and 48°, respectively. In contrast, over grass this factor amounts to 4.9 for a SZA of 86° and a factor of only 1.4 for a SZA of 48°. Thus, a snow surface with high albedo can enhance horizon brightening compared to grass by a factor of 1.7 for low sun at a SZA of 86° and by a factor of 5 for high sun at a SZA of 48°. For cloudy cases, zenith luminance and radiance exceed the cloudless value by a factor of 10 due to multiple scattering between the cloud base and high albedo surface. Measurements of spectral radiance show increased horizon brightening for increasing wavelengths and generally confirm the findings for luminance. Good agreement with model results is found for some cases; however there are also large deviations between measured and modelled values especially in the infrared. These deviations can only partly be explained by measurement uncertainties; to completely resolve the differences between model and measurement further studies need to be performed, which will require an improvement of modelling the spectral radiance. From the present study it can be concluded that a change in albedo conditions, which is predicted as a consequence of climate change, will significantly change the radiation conditions in polar regions as well.

A search for wide visual companions of exoplanet host stars: The Calar Alto Survey

Abstract: We have carried out a search for co-moving stellar and substellar companions around 18 exoplanet host stars with the infrared camera MAGIC at the 2.2 m Calar Alto telescope, by comparing our images with images from the all sky surveys 2MASS, POSS I and II. Four stars of the sample namely HD80606, 55 Cnc, HD46375 and BD–10°3166, are listed as binaries in the Washington Visual Double Star Catalogue (WDS). The binary nature of HD80606, 55 Cnc, and HD46375 is confirmed with both astrometry as well as photometry, thereby the proper motion of the companion of HD46375 was determined here for the first time.We derived the companion masses as well as the longterm stability regions for additional companions in these three binary systems. We can rule out further stellar companions around all stars in the sample with projected separations between 270AU and 2500AU, being sensitive to substellar companions with masses down to ∼60 MJup (S /N = 3). Furthermore we present evidence that the two components of the WDS binary BD–10°3166 are unrelated stars, i.e this system is a visual pair. The spectrophotometric distance of the primary (a K0 dwarf) is ∼67 pc, whereas the presumable secondary BD–10°3166B (a M4 to M5 dwarf) is located at a distance of 13 pc in the foreground. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The method of aperture meridians: a simple calculation tool for applying the ISO/CIE Standard General Sky

Abstract: Following the recent publication of the CIE Standard General Sky,1 adopted as an ISO Standard,2 an Application Guide is expected to be prepared by CIE Technical Committee 3-37 with the aim of explaining and simplifying its practical use. The advantage of the 15 Standard Sky Luminance Distributions (SSLD) adopted by CIE and ISO in relative terms normalized to zenith luminance is not only in the more versatile definition of skylight in various locales and daylight climate regions, but also in the possibility of simulating annual daylight profiles in absolute units based on typical luminance sky patterns. As well as complex computer programs for producing isoluminance contours in plan projections of the sky vault, a simpler tool is needed to calculate absolute sky luminance within the solid angle of arbitrarily dimensioned apertures, especially vertical windows. With this objective in mind, the Method of Aperture Meridians or MAM for any SSLD is introduced in this paper.

Chromaticity of the Martian sky as observed by the Mars Exploration Rover Pancam instruments

Abstract: [1] We have derived quantitative color estimates of the Martian sky from data acquired by the Panoramic Cameras (Pancams) on the Mars Exploration Rovers Spirit and Opportunity. We calculate the perceptual color of the sky directly from the absolute radiometric calibration of the cameras, following similar approaches to those used in previous studies with Viking Lander and Mars Pathfinder data. We further use these measurements to study changes in sky color throughout the MER missions and to compare these to changes in atmospheric opacity determined from direct solar imaging by the Pancams. We have derived a functional relationship between sky color and optical depth and discuss its possible uses and limitations. Finally, we simulate changes in sky color as suspended dust is removed and present visual representations of these based on modeling results, past studies, and observed MER sky brightnesses. The color of the Martian sky as opacity decreases from 1.0 to 0.0 is estimated to change from “dark yellowish brown” at high opacity to “bluish-black” or “black” if dust-free.

Blind component separation for polarized observations of the CMB

Abstract: We present in this paper the PolEMICA (Polarized Expectation-Maximization Independent Component Analysis) algorithm which is an extension to polarization of the SMICA (Spectral Matching Independent Component Analysis) temperature multi-detectors multi-components (MD-MC) component separation method (Delabrouille et al. 2003). This algorithm allows us to estimate blindly in harmonic space multiple physical components from multi-detectors polarized sky maps. Assuming a linear noisy mixture of components we are able to reconstruct jointly the anisotropies electromagnetic spectra of the components for each mode T, E and B, as well as the temperature and polarization spatial power spectra, TT, EE, BB, TE, TB and EB for each of the physical components and for the noise on each of the detectors. PolEMICA is specially developed to estimate the CMB temperature and polarization power spectra from sky observations including both CMB and foreground emissions. This has been tested intensively using as a first approach full sky simulations of the Planck satellite polarized channels for a 14-months nominal mission assuming a simplified linear sky model including CMB, and optionally Galactic synchrotron emission and a Gaussian dust emission. Finally, we have applied our algorithm to more realistic Planck full sky simulations, including synchrotron, realistic dust and free-free emissions.

Design of a new single patch sky and sun simulator

Abstract: The design of a new sky simulator and its construction are described in detail. The simulator, comprising 91 tungsten halogen lamps placed in a hexagonal array, is based on the modelling of one patch of the Tregenza sky hemisphere distribution. This concept allows illuminance measurements from one geometric configuration to be used for every sky model. The sun simulator, which is also comprised of halogen lamps placed in a hexagonal array, is also described. Parallax error measurement and validation studies show that the sky presents low errors. The paper includes a review of existing skies and suns.

Monitoring the night sky with the Cerro Tololo All-Sky camera for the TMT and LSST projects

Abstract: The All-Sky camera used in the LSST and TMT site testing campaigns is described and some early results are shown. The All-Sky camera takes images of the entire visible hemisphere of sky every 30s in blue, red, Y and Z filters giving enhanced contrast for the detection of clouds, airglow and the near-infrared. Animation is used to show movement of clouds. An additional narrow band filter is centered on the most prominent line of the sodium vapor lamp spectra and is used to monitor any man-made light pollution near the site. The camera also detects aircraft lights and contrails, satellites, meteor(ite)s, local light polluters, and can be used for stellar extinction monitoring and for photometry of transient astronomical objects. For outreach and education the All-Sky camera can show wandering planets, diurnal rotation of the sky, the zodiacal light, and similar astronomical basics.

Stray light from galactic sky and zodiacal light for JWST

Abstract: The open telescope design of the James Webb Space Telescope (JWST) allows light from off-axis sources to scatter into the instrument field of view. The significant sources of stray light in the near IR and the mid-infrared waveband are galactic light and reflected sunlight and thermal emission from the zodiacal dust. The stray light from these sources was calculated with the ASAP software. Backward ray tracing was efficiently used in the prediction of the stray light from the sky. Since the galactic and zodiacal light is distributed over the whole sky, the sky was divided into 7200 patches of size 3 degrees by 3 degrees, and the contribution from each patch was calculated. The instrument geometric susceptibility for each sky patch was calculated with backward ray tracing. Multiplying the geometric susceptibility and the sky radiance, we are able to calculate the stray light from each sky patch. Total stray light from the full sky is then calculated by summing the individual patch contributions. The stray light from the galactic sky and zodiacal light has been calculated for different orientations of the observatory relative to the sky.

The Gattini cameras for optical sky brightness measurements in Antarctica

Abstract: The Gattini cameras are two site testing instruments for the measurement of optical sky brightness, large area cloud cover and auroral detection of the night sky above the high altitude Dome C site in Antarctica. The cameras have been in operation since January 2006. The cameras are transit in nature and are virtually identical, both adopting Apogee Alta ccd detectors. The camera called Gattini-SBC images a 6 degree field centred on the South Pole, an elevation of 75° at the Dome C site. The camera takes repeated images of the same 6 degree field in the Sloan g' band (centred on 477nm) and, by adopting a lens with sufficiently long focal length, one can integrate the sky background photons and directly compare to the equivalent values of the stars within the field. The second camera, called Gattini-allsky, incorporates a fish-eye lens and images ~110 degree field centred on local zenith. By taking frequent images of the night sky we will obtain long term cloud cover statistics, measure the sky background intensity as a function of solar and lunar altitude and phase and directly measure the spatial extent of bright aurora if present and when they occur. An overview of the project is presented together with preliminary results from data taken since operation of the cameras in January 2006.