Showing papers on "Sky published in 2004"
TL;DR: The Northern Sky Variability Survey (NSVS) as mentioned in this paper is the most extensive record of stellar variability across the bright sky available today, containing light curves for approximately 14 million objects.
Abstract: The Northern Sky Variability Survey (NSVS) is a temporal record of the sky over the optical magnitude range from 8 to 15.5. It was conducted in the course of the first-generation Robotic Optical Transient Search Experiment (ROTSE-I) using a robotic system of four comounted unfiltered telephoto lenses equipped with CCD cameras. The survey was conducted from Los Alamos, New Mexico, and primarily covers the entire northern sky. Some data in southern fields between declinations 0° and -38° are also available, although with fewer epochs and noticeably lesser quality. The NSVS contains light curves for approximately 14 million objects. With a 1 yr baseline and typically 100–500 measurements per object, the NSVS is the most extensive record of stellar variability across the bright sky available today. In a median field, bright unsaturated stars attain a point-to-point photometric scatter of ~0.02 mag and position errors within 2''. At Galactic latitudes |b| < 20°, the data quality is limited by severe blending due to the ~14'' pixel size. We present basic characteristics of the data set and describe data collection, analysis, and distribution. All NSVS photometric measurements are available for on-line public access from the Sky Database for Objects in Time-Domain (SkyDOT) at Los Alamos National Laboratory. Copies of the full survey photometry may also be requested on tape.
555 citations
TL;DR: The Northern Sky Variability Survey (NSVS) as discussed by the authors is the most extensive record of stellar variability across the bright sky available today, containing light curves for approximately 14 million objects.
Abstract: The Northern Sky Variability Survey (NSVS) is a temporal record of the sky over the optical magnitude range from 8 to 15.5. It was conducted in the course of the first generation Robotic Optical Transient Search Experiment (ROTSE-I) using a robotic system of four co-mounted unfiltered telephoto lenses equipped with CCD cameras. The survey was conducted from Los Alamos, NM, and primarily covers the entire northern sky. Some data in southern fields between declinations 0 and -38 deg is also available, although with fewer epochs and noticeably lesser quality. The NSVS contains light curves for approximately 14 million objects. With a one year baseline and typically 100-500 measurements per object, the NSVS is the most extensive record of stellar variability across the bright sky available today. In a median field, bright unsaturated stars attain a point to point photometric scatter of ~0.02 mag and position errors within 2 arcsec. At Galactic latitudes |b| < 20 deg the data quality is limited by severe blending due to ~14 arcsec pixel size. We present basic characteristics of the data set and describe data collection, analysis, and distribution. All NSVS photometric measurements are available for on-line public access from the Sky Database for Objects in Time-Domain (SkyDOT; this http URL) at LANL. Copies of the full survey photometry may also be requested on tape.
497 citations
TL;DR: In this paper, the sky radiance and luminance distribution models for all sky conditions from clear sky to overcast sky were proposed and compared with the previous models based on the measurement distributions concerning the region of sky vault and the sky conditions.
176 citations
TL;DR: The AGN Physics with the Sloan Digital Sky Survey (SDSS) conference as discussed by the authors brought together groups working inside and outside of the SDSS collaboration at radio through X-ray wavelengths to discuss the common goal of better understanding the physics of AGN.
Abstract: The ``AGN Physics with the Sloan Digital Sky Survey'' conference was held at Princeton University in July 2003 to bring together groups working inside and outside of the SDSS collaboration at radio through X-ray wavelengths to discuss the common goal of better understanding the physics of Active Galactic Nuclei (AGN). Although we still do not have a full understanding of AGN, much progress has been made in recent years. In this conference summary, we concentrate on those topics discussed at the meeting where we believe that there has been significant change or where there is a new standard of comparison, as well as on important new trends in AGN research.
123 citations
TL;DR: It is found that the celestial E-vector pattern generally follows the Rayleigh pattern well, which is a fundamental hypothesis in the studies of animal orientation and human navigation with the use of the celestial alpha pattern.
Abstract: We present the first high-resolution maps of Rayleigh behavior in clear and cloudy sky conditions measured by full-sky imaging polarimetry at the wavelengths of 650 nm (red), 550 nm (green), and 450 nm (blue) versus the solar elevation angle θs. Our maps display those celestial areas at which the deviation Δα= |αmeas- αRayleigh| is below the threshold αthres=5°, where αmeas is the angle of polarization of skylight measured by full-sky imaging polarimetry, and αRayleigh is the celestial angle of polarization calculated on the basis of the single-scattering Rayleigh model. From these maps we derived the proportion r of the full sky for which the single-scattering Rayleigh model describes well (with an accuracy of Δα=5°) the E-vector alignment of skylight. Depending on θs,r is high for clear skies, especially for low solar elevations (40%
118 citations
TL;DR: In this article, the multiwavelength properties of 291 type II AGN candidates (0.3 < z < 0.8) selected based on their optical emission line properties from the spectroscopic database of the Sloan Digital Sky Survey were studied.
Abstract: Type II quasars are luminous AGNs whose central engines and broad-line regions are obscured by intervening material; such objects only recently have been discovered in appreciable numbers. We study the multiwavelength properties of 291 type II AGN candidates (0.3 < z < 0.8) selected based on their optical emission line properties from the spectroscopic database of the Sloan Digital Sky Survey. This sample includes about 150 objects luminous enough to be classified as type II quasars. We matched the sample to the FIRST (20 cm), IRAS (12-100 micron), 2MASS (JHK_S) and RASS (0.1-2.4 keV) surveys. Roughly 10% of optically selected type II AGN candidates are radio-loud, comparable to the AGN population as a whole. About 40 objects are detected by IRAS at 60 micron and/or 100 micron, and the inferred mid/far-IR luminosities lie in the range nu L_nu=10^45-3x10^46 erg/sec. Average IR-to-[OIII]5007 ratios of objects in our sample are consistent with those of other AGNs. Objects from our sample are ten times less likely to have soft X-ray counterparts in RASS than type I AGNs with the same redshifts and [OIII]5007 luminosities. The few type II AGN candidates from our sample that are detected by RASS have harder X-ray spectra than those of type I AGNs. The multiwavelength properties of the type II AGN candidates from our sample are consistent with their interpretation as powerful obscured AGNs.
112 citations
TL;DR: The Extended Source Catalog (XSC) as discussed by the authors represents a uniquely unbiased sample of nearby galaxies, particularly sensitive to the underlying, dominant, stellar mass component of galaxies, and employs a photometric redshift technique to add depth to the spatial maps.
Abstract: Using twin ground-based telescopes, the Two-Micron All Sky Survey (2MASS) scanned both equatorial hemispheres, detecting more than 500 million stars and resolving more than 1.5 million galaxies in the near-infrared (1-2.2 µm) bands. The Extended Source Catalog (XSC) embodies both photometric and astrometric whole sky uniformity, revealing large scale structures in the local Universe and extending our view into the Milky Way's dust-obscured 'Zone of Avoidance'. The XSC represents a uniquely unbiased sample of nearby galaxies, particularly sensitive to the underlying, dominant, stellar mass component of galaxies. The basic properties of the XSC, including photometric sensitivity, source counts, and spatial distribution, are presented here. Finally, we employ a photometric redshift technique to add depth to the spatial maps, reconstructing the cosmic web of superclusters spanning the sky.
109 citations
TL;DR: In this paper, a catalog of 8678 slowly varying stars with near-infrared colors corresponding to the evolved asymptotic giant branch population was presented, and the use of support vector machines, a modern machine-learning algorithm, can reliably distinguish Mira variables from other types of red variables, namely, semiregular and irregular.
Abstract: We present a catalog of 8678 slowly varying stars with near-infrared colors corresponding to the evolved asymptotic giant branch population. Objects were selected from the Northern Sky Variability Survey (NSVS) covering the entire sky above declination δ = -38° in a single unfiltered photometric band corresponding to a V-band magnitude range of ~8–15.5 mag. After quality cuts, the number of measurements for a typical star is approximately 150, but it ranges up to ~1000 for high-declination stars. We show that the use of support vector machines, a modern machine-learning algorithm, can reliably distinguish Mira variables from other types of red variables, namely, semiregular and irregular. We also identify a region of parameter space that is dominated by carbon stars. Our classification is based on period, amplitude, and three independent colors possible with photometry from the NSVS and the Two Micron All Sky Survey. The overall classification accuracy is ~90% despite the relatively short survey baseline of 1 yr and limited set of features. There are 6474 stars in our sample without identifications in the General Catalogue of Variable Stars, which, as such, are most likely new discoveries. Period-amplitude and period-color diagrams of both our previously known and newly identified Mira stars are in good agreement with published studies based on smaller samples.
108 citations
01 Aug 2004
TL;DR: In this paper, an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 A was used to study the wavelength dependence of quasar variability.
Abstract: SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for ~2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 A. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index αλ = -2.00, compared to an index of αλ = -1.35 for the single-epoch spectrum. This confirms that quasar continua are bluer when brighter. The difference spectrum also exhibits very weak or absent emission-line features; the strongest emission lines vary only 30% as much as the continuum. This small emission-line variability with respect to the continuum is consistent with the intrinsic Baldwin effect. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for λrest < 2500 A, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.
106 citations
TL;DR: In this paper, the frequency of occurrence of General Sky types from International Daylight Measurement Programme sky scan data is derived from the CIE Standard General Sky, which consists of a family of luminance distributions which can be matched to measured sky brightness patterns.
Abstract: The CIE Standard General Sky consists of a family of luminance distributions which can be matched to measured sky brightness patterns. The daylight climate of a site can be described concisely and effectively by the statistical distribution of the General Sky types that best fit the sky luminance patterns that occur there. This paper gives a procedure for deriving the frequency of occurrence of General Sky types from International Daylight Measurement Programme sky scan data. Measured luminances are normalized with respect to horizontal illuminance and solar elevation, then the sky types giving the best least-squares fit are found. A data structure for daylight climate simulation is proposed.
92 citations
TL;DR: The first phase of the search, discussed in this article, was centered on the south celestial pole and covers declinations from −90° to −575 degrees, and five new objects with proper motions between 10 and 26 yr-1 were discovered via a new Research Consortium on Nearby Stars (RECONS) search for high proper motion stars using the SuperCOSMOS Sky Survey.
Abstract: Five new objects with proper motions between 10 and 26 yr-1 have been discovered via a new Research Consortium on Nearby Stars (RECONS) search for high proper motion stars using the SuperCOSMOS Sky Survey. The first portion of the search, discussed here, is centered on the south celestial pole and covers declinations -90° to -575. Photographic photometry from SuperCOSMOS and JHKs near-infrared photometry from the Two Micron All Sky Survey for stars nearer than 10 pc are combined to provide a suite of new M-color relations useful for estimating distances to main-sequence stars. These relations are then used to derive distances to the new proper motion objects, as well as previously known stars with μ ≥ 10 yr-1 (many of which have no trigonometric parallaxes) recovered during this phase of the survey. Four of the five new stars have red dwarf colors, while one is a nearby white dwarf. Two of the red dwarfs are likely to be within the RECONS 10 pc sample, and the white dwarf probably lies between 15 and 25 pc. Among the 23 known stars recovered during the search, there are three additional candidates for the RECONS sample that have no trigonometric parallaxes.
TL;DR: In this paper, a search of more than 3000 deg2 of high-latitude sky by the Sloan Digital Sky Survey (SDSS) has yielded 251 faint highlatitude carbon stars (FHLCs), the large majority previously uncataloged.
Abstract: A search of more than 3000 deg2 of high-latitude sky by the Sloan Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs), the large majority previously uncataloged. We present homogeneous spectroscopy, photometry, and astrometry for the sample. The objects lie in the 15.6 < r < 20.8 range and exhibit a wide variety of apparent photospheric temperatures, ranging from spectral types near M to as early as F. Proper-motion measurements for 222 of the objects show that at least 50%, and quite probably more than 60%, of these objects are actually low-luminosity dwarf carbon (dC) stars, in agreement with a variety of recent, more limited investigations that show that such objects are the numerically dominant type of star with C2 in the spectrum. This SDSS homogeneous sample of ~110 dC stars now constitutes 90% of all known carbon dwarfs and will grow by another factor of 2–3 by the completion of the survey. As the spectra of the dC and the faint halo giant C stars are very similar (at least at spectral resolution of 103), despite a difference of 10 mag in luminosity, it is imperative that simple luminosity discriminants other than proper motion be developed. We use our enlarged sample of FHLCs to examine a variety of possible luminosity criteria, including many previously suggested, and find that, with certain important caveats, JHK photometry may segregate dwarfs and giants.
TL;DR: In this article, some common climatic parameters including cloud cover, sunshine hour, solar irradiance, daylight illuminance and sky luminance and their applications in the classification of sky conditions have been established.
TL;DR: A search of more than 3,000 square degrees of high latitude sky by the Sloan Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs), the large majority previously uncataloged.
Abstract: A search of more than 3,000 square degrees of high latitude sky by the Sloan Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs), the large majority previously uncataloged. We present homogeneous spectroscopy, photometry, and astrometry for the sample. The objects lie in the 15.6 < r < 20.8 range, and exhibit a wide variety of apparent photospheric temperatures, ranging from spectral types near M to as early as F. Proper motion measurements for 222 of the objects show that at least 50%, and quite probably more than 60%, of these objects are actually low luminosity dwarf carbon (dC) stars, in agreement with a variety of recent, more limited investigations which show that such objects are the numerically dominant type of star with C_2 in the spectrum. This SDSS homogeneous sample of ~110 dC stars now constitutes 90% of all known carbon dwarfs, and will grow by another factor of 2-3 by the completion of the Survey. As the spectra of the dC and the faint halo giant C stars are very similar (at least at spectral resolution of 1,000) despite a difference of 10 mag in luminosity, it is imperative that simple luminosity discriminants other than proper motion be developed. We use our enlarged sample of FHLCs to examine a variety of possible luminosity criteria, including many previously suggested, and find that, with certain important caveats, JHK photometry may segregate dwarfs and giants.
TL;DR: In this paper, the authors constrain the evolution in the comoving space density for low-luminosity radio sources as a function of cosmic epoch by matching deep radio surveys with the Sloan Digital Sky Survey (SDSS).
Abstract: In this paper we constrain the evolution in the comoving space density for low-luminosity [typically Fanaroff-Riley type I (FRI)] radio sources as a function of cosmic epoch by matching deep radio surveys [Westerbork Northern Sky Survey (WENSS), Faint Images of the Radio Sky at Twenty-centimetres (FIRST) and NRAO VLA Sky Survey (NVSS)] with the Sloan Digital Sky Survey (SDSS). This results in 1014 matched radio sources covering an effective area of 0.217 sr, 686 with L 325 MHz < 10 25 W Hz -1 sr -1 , which is an order of magnitude larger than any previous study at these luminosities. Using the non-parametric V/V max test we show that low-luminosity radio sources evolve differently from their more powerful, predominantly Fanaroff-Riley type II (FRII), counterparts. Indeed, we find that the lower luminosity population is consistent with a constant comoving space density with redshift, as opposed to the strong positive evolution for the more powerful sources.
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15 Dec 2004TL;DR: In this paper, a method of detecting sky in a digital color image having pixels includes identifying pixels from the digital colour image representing an initial sky region, developing a model based on the identified sky pixels wherein such model is a mathematical function that has inputs of pixel position and outputs of color.
Abstract: A method of detecting sky in a digital color image having pixels includes identifying pixels from the digital color image representing an initial sky region, developing a model based on the identified sky pixels wherein such model is a mathematical function that has inputs of pixel position and outputs of color, and using the model to operate on the digital color image to classify additional pixels not included in the initial sky region as sky.
TL;DR: In this article, the authors carried out a radio-wavelength imaging survey of 45 bright-rimmed clouds (BRCs), using the Australia Telescope Compact Array to characterise the physical properties in their ionised boundary layers.
Abstract: We have carried out a radio-wavelength imaging survey of 45 bright-rimmed clouds (BRCs), using the Australia Telescope Compact Array to characterise the physical properties in their ionised boundary layers. We detected radio emission from a total of 25 clouds and using a combination of Digitised Sky Survey and mid-infrared MSX 8 µm images classified the emission into that associated with the ionised cloud rims, that associated with embedded possible massive YSOs and that unlikely to be associated with the clouds at all. A total of 18 clouds display radio emission clearly associated with the cloud rim and we determine the ionising photon flux illuminating these clouds and the electron density and pressure of their ionised boundary layers. Using a global estimate for the interior molecular pressure of these clouds we show that the majority are likely to be in pressure equilibrium and hence are currently being shocked by photoionisation-induced shocks. We identify those clouds where the predicted ionising photon flux is inconsistent with that derived from the observations and show that either the spectral types of the stars illuminating the BRCs are earlier than previously thought or that there must be additional ionising sources within the HII regions. Finally, we identify the radio sources embedded within the clouds with infrared stellar clusters and show that they contain late O and early B-type stars, demonstrating that a number of BRCs are intimately involved with high to intermediate-mass star formation.
TL;DR: In this paper, an archival radio, optical and infrared wavelength imaging survey of 44 bright-rimmed clouds (BRCs) using the NRAO/VLA Sky Survey (NVSS) archive, images from the Digitised Sky Survey and the Midcourse Space eXperiment (MSX) was carried out.
Abstract: We have carried out an archival radio, optical and infrared wavelength imaging survey of 44 Bright-Rimmed Clouds (BRCs) using the NRAO/VLA Sky Survey (NVSS) archive, images from the Digitised Sky Survey (DSS) and the Midcourse Space eXperiment (MSX). The data characterise the physical properties of the Ionised Boundary Layer (IBL) of the BRCs. We have classified the radio detections as: that associated with the ionised cloud rims; that associated with possible embedded Young Stellar Objects (YSOs); and that unlikely to be associated with the clouds at all. The stars responsible for ionising each cloud are identified and a comparison of the expected ionising flux to that measured at the cloud rims is presented. A total of 25 clouds display 20 cm radio continuum emission that is associated with their bright optical rims. The ionising photon flux illuminating these clouds, the ionised gas pressure and the electron density of the IBL are determined. We derive internal molecular pressures for 9 clouds using molecular line data from the literature and compare these pressures to the IBL pressures to determine the pressure balance of the clouds. We find three clouds in which the pressure exerted by their IBLs is much greater than that measured in the internal molecular material. A comparison of external pressures around the remaining clouds to a global mean internal pressure shows that the majority of clouds can be expected to be in pressure equilibrium with their IBLs and hence are likely to be currently shocked by photoionisation shocks. We identify one source which shows 20 cm emission consistent with that of an embedded high-mass YSO and confirm its association with a known infrared stellar cluster. This embedded cluster is shown to contain early-type B stars, implying that at least some BRCs are intimately involved in intermediate to high mass star formation.
TL;DR: In this article, the authors discuss the light trapping of insects depending on the environmental illu- mination, twilight polarization phenomena and the moon phases, and the trapping data were taken of Hun- garian national light-trap network.
Abstract: The present study discusses the light trapping of insects depending on the environmental illu- mination, twilight polarization phenomena and the moon phases. The trapping data were taken of Hun- garian national light-trap network. The important results are the followings: The Babinet-point, a polariza- tion free spot of the sky at twilight, can be a role of orientation of insects. The height of the Moon above the horizon is in negative correlation with the number of the caught insects. The maximum individual number of species was collected at various moon phases.
TL;DR: In this paper, the sky brightness, naked eye stellar visibility and telescope limiting magnitude are produced as three-dimensional arrays, the axes of which are the position on the sky and the atmospheric clarity.
Abstract: We apply the sky brightness modelling technique introduced and developed by Roy Garstang to high-resolution satellite measurements of upward artificial light flux carried out with the US Air Force Defense Meteorological Satellite Program Operational Linescan System and to GTOPO30 (a global digital elevation model by the US Geological Survey's EROS Data Centre) digital elevation data in order to predict the brightness distribution of the night sky at a given site in the primary astronomical photometric bands for a range of atmospheric aerosol contents. This method, based on global data and accounting for elevation, Earth curvature and mountain screening, allows the evaluation of sky glow conditions over the entire sky for any site in the world, to evaluate its evolution, to disentangle the contribution of individual sources in the surrounding territory and to identify the main contributing sources. Sky brightness, naked eye stellar visibility and telescope limiting magnitude are produced as three-dimensional arrays, the axes of which are the position on the sky and the atmospheric clarity. We compare our results with available measurements.
TL;DR: In this article, the sky luminance data recorded from January 1999 to December 2001 in Hong Kong and generated by two well-known sky-luminance models (Kittler and Perez) were used to compute the outdoor illuminance for the four principal vertical planes (N, E, S and W).
TL;DR: In this article, a review of wide-angle polarization CCD-measurements of the twilight sky in V and R color bands with effective wavelengths 550 and 700 nm is presented.
Abstract: The paper presents a review of a number of wide-angle polarization CCD-measurements of the twilight sky in V and R color bands with effective wavelengths 550 and 700 nm. The basic factors affecting (usually decreasing) the polarization of the twilight sky are the atmospheric aerosol scattering and multiple scattering. These effects were distinguished from each other, and a method of multiple-scattering separation is discussed. The results are compared with the data of numerical simulation of radiative transfer in the atmosphere for different aerosol models. The whole twilight period is divided into different stages with different mechanisms forming the twilight-sky polarization properties.
TL;DR: In this paper, an analysis of daylight and solar radiation data in low latitude/tropics area has been done, which classified three sky conditions: clear sky, intermediate sky and overcast sky.
TL;DR: The Sky Polarization Observatory (SPOrt) as discussed by the authors is an ASI-funded experiment specifically designed to measure the sky polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be flown on the International Space Station.
TL;DR: In this article, the authors present the photometric calibration technique for the Digitized Second Palomar Observatory Sky Survey, used to create seamless catalogs of calibrated objects over large sky areas.
Abstract: We present the photometric calibration technique for the Digitized Second Palomar Observatory Sky Survey, used to create seamless catalogs of calibrated objects over large sky areas. After applying a correction for telescope vignetting, the extensive plate overlap regions are used to transform sets of plates onto a common instrumental photometric system. Photometric transformations to the Gunn gri system for each plate, for stars and galaxies, are derived using these contiguous stitched areas and an extensive CCD imaging library obtained for this purpose. We discuss the resulting photometric accuracy, survey depth, and possible systematic errors.
24 Oct 2004
TL;DR: A novel algorithm is proposed based on a two-dimensional polynomial model of the image of blue sky to establish high-confidence blue sky regions and correctly increased the belief values on 6 regions found by the initial sky detector.
Abstract: Blue sky commonly appears in photographs. Reliable detection of blue sky can aid semantic image retrieval, image understanding and image enhancement. A novel algorithm is proposed based on a two-dimensional polynomial model of the image of blue sky. An initial sky detection is used to establish high-confidence blue sky regions. Candidate sky regions are found and a two-dimensional polynomial model is used to compute the belief that a given region is also sky. On a database of 83 images, the algorithm correctly classified 31 additional regions as blue sky while adding 8 minor false positives, most of them reflections of sky. Further, the algorithm correctly increased the belief values on 6 regions found by the initial sky detector.
TL;DR: In this paper, the identification of sky luminance patterns using three common climatic elements, namely cloud cover (CLD), sunshine hour (SH) and clearness index (K t ), is presented.
Abstract: A good understanding of the sky luminance distribution is essential for efficient daylight-ing designs and developments. Sky luminance patterns are always modeled under various sky conditions using climatic parameters as weighting factors to indicate the degree of sky clearness. This paper presents the work on the identification of sky luminance patterns using three common climatic elements, namely cloud cover (CLD), sunshine hour (SH) and clearness index (K t ). Three sky types representing overcast, partly cloudy and clear were selected from the Kittler et al. 15 standard skies. It has been shown that sky conditions classified by individual sky indicators produced acceptable agreements with the measured data. In general, CLD shows the best results, followed by K t , then SH. Better results in terms of the frequency of occurrence and root mean square errors can be found when CLD and SH are jointly utilised to describe the sky conditions.
TL;DR: In this article, the sky surface brightness at the Vatican Advanced Technology Telescope (VATT) was measured during 16 observing runs between 1999 April and 2003 December, with an average low air mass (sec z < 1.2) sky surface intensity of 22.00, 22.53, 21.72, and 21.19 mag arcsec 2 in U, B, V, and R, respectively.
Abstract: We present measurements of sky surface brightness and seeing on Mount Graham, obtained at the Vatican Advanced Technology Telescope (VATT) during 16 observing runs between 1999 April and 2003 December. We show that the sky surface brightness is significantly darker during photometric conditions and can be highly variable over the course of a single observing run, as well as from one run to the next, regardless of photometricity. In our photometric observations, we find an average low air mass (sec z<1.2) sky surface brightness of 22.00, 22.53, 21.49, and 20.88 mag arcsec?2 in U, B, V, and R, respectively. The darkest run (2000 February in U and 2001 February in BVR) had an average sky surface brightness of 22.38, 22.86, 21.72, and 21.19 mag arcsec?2 in U, B, V, and R, respectively. With these results, we show that under the best conditions, Mount Graham can compete with the darkest sites in Hawaii and Chile, thanks in part to the strict dark?sky ordinances in place in Tucson and Safford. We expect the sky over Mount Graham to be even darker than our 1999?2003 results during solar minimum (2006?2007). We find a significant improvement of about 0 45 in our measured stellar FWHM after improvements to the telescope were made in summer and fall 2001. Stellar FWHM values are highly variable, with median R?band focus FWHM values in each observing run ranging from 0 97 to 2 15. Significant subarcsecond seeing was occasionally achieved, with values as low as 0 65 FWHM in R. There may still be a significant telescope contribution to the seeing at the VATT, but nearby trees as high as the dome are currently the dominant factor.