Showing papers on "Sky published in 1997"
TL;DR: In this paper, the authors describe how huge amounts of data produced by sky surveys from the ground and in space will eventually merge into a multi-wavelength virtual sky, and in many cases, astronomers will make more efficient "observations" through their computer terminal accessing databases rather than at a telescope.
Abstract: Considerable changes are under way in the practice of observational astronomy due to the improvements of panoramic detectors, the increasing archiving capacity of computers and the acceleration of communication networks. The huge amounts of data produced by sky surveys from the ground and in space will eventually merge into a multiwavelength virtual sky, and in many cases, astronomers will make more efficient “observations” through their computer terminal accessing databases rather than at a telescope.
325 citations
01 Jan 1997
TL;DR: The Two Micron All Sky Survey (2MASS) project as discussed by the authors was the first to map the entire sky in the J (1.13−1.37 νm), H (1,50−1,1.50 μm), and K s (2.00−2.32 μm) photometric bands to a 3σ limiting sensitivity of 17.1, 16.4 and 15.6 niag, respectively.
Abstract: Beginning in early 1997, the Two Micron All Sky Survey (2MASS) project will map the entire sky in the J (1.13–1.37 νm), H (1.50–1.50 μm), and K s (2.00–2.32 μm) photometric bands to a 3σ limiting sensitivity of 17.1, 16.4 and 15.6 niag, respectively. Often these flux limits are presented as 10σ values (15.8, 15.1, and 14.3 mag, respectively) since this flux level sets the point source completeness (0.99) and reliability (0.9995) regnirernents. The pixel size for the survey is 2.0“. The survey cameras (one for each hemisphere) each contain three NICMOS3 arrays which similtaneously image an 8.5’×8.5’ field in all three survey wavebands. The 1.3 ni survey telescopes scan steadily in declination at a rate of about one arcminute per second while the telescope secondary mirror tilts in the opposite direction to freeze the focal plane position on the sky. Subsequent frames overlap by 84% so that each pixel on the sky is exposed at six dithered positions relative to pixel centers. The frame exposure time is 1.3 seconds.
234 citations
TL;DR: In this paper, several very simple clear sky and cloudy sky global irradiance models were tested under the climate and latitudes of Romania (Eastern Europe) and the results showed that the performance of the very simple cloudy sky models is comparable to that of the more complicated ones.
127 citations
Journal Article•
TL;DR: The All Sky Automated Survey (ASAS) as discussed by the authors uses multi-pixel CCD detectors and low cost computers to monitor as many variable objects in the sky as feasible with current technology and the available funds.
Abstract: The All Sky Automated Survey (ASAS) uses multi-pixel CCD detectors and low cost computers to monitor as many variable objects in the sky as feasible with current technology and the available funds. ASAS uses amateur scale instruments and mostly off the shelf hardware. The project has demonstrated that, even among stars brighter than 13 magnitude, 90% of variables have not been discovered yet. Using a 10-cm aperture it is possible to detect red giants across our Galaxy and to monitor huge numbers of variable stars in the Large and Small Magellanic Clouds. Many of these stars are too bright for a 1-meter class telescope. The very low cost of ASAS hardware makes it accessible to amateurs and small colleges, assuming a complete software package is provided. It is expected that the project will keep growing exponentially with time, and will remain an ever-growing source of data for virtual observatories as well as a major source of alerts for new variable stars, AGNs, and asteroids.
118 citations
TL;DR: In this paper, the sky radiance was modeled from ensembled measurements according to the standard overcast sky radiometric distribution for each of the wavelength bands of ultraviolet-B, ultraviolet-A and photosynthetically active radiation (0.40-0.70 μm) in a rural area.
Abstract: Sky radiance measurements in the wavelength bands of ultraviolet-B (0.28–0.32 μm), ultraviolet-A (0.32–0.40 μm), and photosynthetically active radiation (0.40–0.70 μm) were made under obscured overcast skies in a rural area. Radiance distributions were modeled for seven measurement scans with solar zenith angles varying from 19° to 49°. For the seven scans, the atmospheric transmittance of photosynthetically active photon flux density varied from 0.16 to 0.25. The corresponding fraction of cloud-free sky photosynthetically active photon flux density ranged from 0.21 to 0.32. The corresponding fraction of ultraviolet-B cloud-free sky irradiance was between 0.20 and 0.34, with typically lower fractions of cloud-free sky irradiance in the ultraviolet-B than in the photosynthetically active photon flux density. The sky radiance was modeled from the ensembled measurements according to the standard overcast sky radiance distribution for each of the wavelength bands. Although the ultraviolet wave bands ...
65 citations
TL;DR: In this article, a data base of V-band and B-band night-sky brightness measurements rather evenly spread out over the course of a whole sunspot cycle from September 1985 to August 1996 was produced.
Abstract: We have produced a data base of V-band and B-band night-sky brightness measurements rather evenly spread out over the course of a whole sunspot cycle from September 1985 to August 1996 Almost all the data were obtained at the 2800-m level of Mauna Kea using the same telescope, same photomultiplier tube, filters, and diaphragm, thus minimizing various sources of systematic error and allowing an estimate of the sources of random error The yearly V-band averages of observed sky brightness ranged from 21287 to 21906 magnitudes per square arc second The color of the sky is B-V = 0930 and does not change discernibly over the course of the sunspot cycle After correcting the V-band data to the zenith, we find that the airglow component varied a factor of 45 over the course of the solar cycle Once the 11-year solar cycle effect is removed from the data, the most significant contribution to the scatter of individual data points appears to be the short term variations on time scales of tens of minutes like those observed by the Whole Earth Telescope project
64 citations
TL;DR: In this article, the distribution of clear sky radiance was measured and modeled for wavelength bands of ultraviolet-B (280-320 nm) and ultraviolet-A (320-400 nm).
Abstract: In the ultraviolet, the diffuse sky radiation component is often at least 50% of the global irradiance for middle latitudes. Thus, knowledge of the sky radiance distribution is important for modeling ultraviolet irradiance in vegetative or urban canopies. In this study, the distribution of clear sky radiance was measured and modeled for wavelength bands of ultraviolet-B (280–320 nm) and ultraviolet-A (320–400 nm). Sky radiance measurements were made in a rural area over a wide range of solar zenith angles using radiance sensors mounted on a hand-operated hemispherical rotation mount. The measured sky radiance distribution in the UVA waveband differed greatly from that in the UVB waveband. The sky UVB radiance varied less across the sky hemisphere than the sky UVA radiance, in accordance with theory. A distinct region of minimum sky radiance was commonly found in the UVA waveband, but not the UVB waveband.
60 citations
01 Feb 1997
54 citations
TL;DR: In this paper, deep imaging at 6.7 and 15 μm from the CAM instrument on the Infrared Space Observatory (ISO) centred on the Hubble Deep Field (HDF) is presented.
Abstract: We present deep imaging at 6.7 and 15 μm from the CAM instrument on the Infrared Space Observatory (ISO) , centred on the Hubble Deep Field (HDF). These are the deepest integrations published to date at these wavelengths in any region of sky. We discuss the observational strategy and the data reduction. The observed source density appears to approach the CAM confusion limit at 15 μm, and fluctuations in the 6.7-μm sky background may be identifiable with similar spatial fluctuations in the HDF galaxy counts. ISO appears to be detecting comparable field galaxy populations to the HDF, and our data yield strong evidence that future infrared missions (such as SIRTF , FIRST and WIRE ) as well as SCUBA and millimetre arrays will easily detect field galaxies out to comparably high redshifts.
TL;DR: In this article, the distribution of sky radiance was measured in a rural area and modeled for wavelength bands of ultraviolet-B (UVB, 280-320 nm) and ultraviolet-A (UVA, 320-400 nm).
Abstract: The diffuse sky radiation component in the ultraviolet wavelengths is often at least 50% of the global irradiance under clear skies, and is the dominant component of ultraviolet global radiation under translucent overcast skies. The distribution of sky radiance was measured in a rural area and modeled for wavelength bands of ultraviolet-B (UVB, 280–320 nm) and ultraviolet-A (UVA, 320–400 nm). Sky radiance measurements were made during the summer of 1993 over a wide range of solar zenith angles using radiance sensors mounted on a hand-operated hemispherical rotation mount. UVB irradiance measurements were also made during each scan. Since the ratio of measured irradiance under overcast skies and that predicted for clear skies was not correlated with cloud base height, opaque cloud fraction, or solar zenith angle, it was concluded that the scattering from the clouds dominated the global irradiance, and this scattering was relatively unaffected by the scattering off opaque clouds in the translucent atmosphere.
Journal Article•
Abstract: FEROS is a fiber-fed bench-mounted prism-crossdispersed echelle spectrograph for the ESO 1.52-m telescope at La Silla. It works in quasi Littrow mode and in white pupil configuration. For the object and the nearby sky, the complete optical spectrum from 370–860 nm is recorded in one exposure with a resolving power of R = 48,000 by the use of a two-beam, two-slice image slicer. A first concept of FEROS, which is supposed to replace ECHELEC at the 1.52-m telescope, was presented by Pasquini et al., 1992, “FEROS for the ESO 1.52-m Telescope”, 32nd Scientific Technical Committee Meeting, Garching. Designed as a fiber-linked spectrograph connected to the permanently mounted Boller & Chivens spectrograph it has the advantage of being always available. The fibre entrance of FEROS is mounted on the slit unit of the Boller & Chivens spectrograph, and it will be possible to change from one spectrograph to the other by a simple translation of the slit unit. Because FEROS provides highdispersion spectroscopy with a wide, simultaneous wavelength coverage, this instrument mounted on an intermediatesize telescope fills a gap in the present and future ESO instrumentation park. It will allow to realise many important scientific programmes (a few of which are described below) of objects down to about 16th magnitude with high efficiency, little constraints on operations and will relieve the pressure on larger telescopes. FEROS is built for ESO by a consortium of four astronomical institutes under the leadership of the Landessternwarte Heidelberg (LSW). The Principal Investigator (PI) of the FEROS project is Prof. Dr. Bernhard Wolf at the LSW. Further members of the consortium are the Astronomical Observatory Copenhagen (AOC), the Institut d’Astrophysique de Paris (IAP), and the Observatoire de Paris/Meudon (OPM). The contract between ESO and the FEROS Consortium was signed in September 1996. It is planned that the instrument will be available to the community in early 1999. Scientific Objectives
TL;DR: This paper proposes a fast display method of the sky colour by expressing the intensity distribution of the Sky Colour using basis functions, even if the sun position and/or the camera position are altered.
Abstract: Computer graphics are being used for visual environmental assessment or architectural designs Displaying the sky as a background is indispensable in generating photorealistic images for such applications In this paper, we propose a fast display method of the sky colour by expressing the intensity distribution of the sky using basis functions, even if the sun position and/or the camera position are altered In the proposed method, cosine functions are used as basis functions The sun altitude is altered at certain intervals and the distributions of the sky colour for each sun altitude are precalculated and stored efficiently using basis functions The colour of the sky in the view direction of an arbitrary sun position can be obtained from the stored distributions and displayed quickly © 1997 by John Wiley & Sons, Ltd
TL;DR: In this article, the authors presented a mathematical broadband model for the density of solar radiation energy incident on a tilted surface of the Earth with an arbitrary tilting angle, using vector calculus.
TL;DR: In this article, small angular displacements of the CCD, telescope, and instrument, with respect to the external light source (dome, sky, etc.) yields a corresponding linear translation of the image on the camera with respect the true flat field function, and hence enables a flat field frame to be generated that is independent of the illumination source.
Abstract: Precision CCD photometry over large fields-of-view and detection of very faint or diffuse objects demand great care in the acquisition of flat-field frames. Variations in the illuminated field, either in the sky or with locally illuminated dome screens, will introduce spatial variability, or gradient structure, in the flat field frame. This is a concern for the Hubble Space Telescope which cannot make use of twilight or dome flats. The physics of generating flat-field frames must account for the characterisitics and structure of the CCD, the instrument and telescope optics, and the illumination source. Recognizing that small angular displacements of the CCD, telescope, and instrument, with respect to the external light source (dome, sky, etc.) yields a corresponding linear translation of the image on the CCD with respect to the true flat-field function, we can derive a functional equation that can be solved and hence enables a flat-field frame to be generated that is independent of the illumination source. This equation can be generalized to two-dimensions approximating an elliptic partial differential equation relating the offset CCD measurements to the flat-field function. This technique may benefit faint deep-field photometric wide field-of-view observations, the HST, and cameras on spacecraft and planetary landers.
TL;DR: In this paper, the sky conditions can be identified in the absence of sky scanning and cloudiness information in the presence of sky scans and bin-selection methods using data recorded in Bratislava, Slovakia during 1995.
Abstract: Exterior illuminance data recorded at regular one-minute intervals and simultaneous zenith sky luminance have been gathered as part of the International Daylight Measurement Programme. Data measured at several locations characterise luminous climate and the frequency of occurrence of typical sky patterns reflecting local variations. Zenith vector luminance has a direct influence on the resulting (scalar) horizontal diffuse/sky illuminance level. Thus their ratio usually indicates the prevailing character of the sky luminance distribution. Sophisticated parametrisation and 'bin' selection methods have been used to analyse data recorded in Bratislava, Slovakia during 1995. Examples are shown of how frequent and specific sky conditions can be identified in the absence of sky scanning and cloudiness information.
TL;DR: In this article, the authors describe a multi-fibre positioner, MEFOS, that was in generaluse at the La Silla Observatory, and implemented at the prime focus of the ESO 3.6 m telescope.
Abstract: We are describing a new multi-fibre positioner, MEFOS, that was in generaluse at the La Silla Observatory, and implemented at the prime focus of theESO 3.6 m telescope. It is an arm positioner using 29 arms in a one degreefield. Each arm is equipped with an individual viewing system for accuratesetting and carries two spectroscopic fibres, one for the astronomical objectand the other one for the sky recording needed for sky subtraction. Thespectral fibres intercept 2.5 arcsec on the sky and run from the prime focusto the Cassegrain, where the B&C spectrograph is located. Afterdescribing the observational procedure, we present the first scientificresults.
TL;DR: In this paper, a multi-spectral polarimeter (FPR1000) is designed to measure the radiance and degree of polarization of the sky radiation as well as the extinction of solar irradiance using the same optical system.
Abstract: A multi-spectral polarimeter (FPR1000) is designed to measure the radiance and degree of polarization of the sky radiation as well as the extinction of solar irradiance using the same optical system. This enables us to make consistent measurements of the direct solar and diffused sky radiation. Measurements are made at the same wavelength regions as Polarization and Directionality of the Earth’s Reflectances (POLDER) and Ocean Color and Temperature Scanner (OCTS) onboard Advanced Earth Observing Satellite (ADEOS). Based on measurements for the Langley plot calibration made at Mauna Loa Observatory, the calibration constants are obtained by considering the effect of absorption by water vapor and uniformly mixed gas. Preliminary analyses of the measurements of sky radiation and direct solar irradiance carried out in the western part of the Pacific Ocean are presented. Combined measurements of the extinction of solar irradiance, and the radiance and degree of polarization of sky radiation could be useful in improving retrieval of optical characteristics of aerosol and for atmospheric correction.
TL;DR: In this article, a data set of V-band and B-band night-sky brightness measurements rather evenly spread out over the course of a whole sunspot cycle from September 1985 to August 1996 was produced.
Abstract: We have produced a data base of V-band and B-band night-sky brightness measurements rather evenly spread out over the course of a whole sunspot cycle from September 1985 to August 1996. Almost all the data were obtained at the 2800-m level of Mauna Kea using the same telescope, same photomultiplier tube, filters, and diaphragm, thus minimizing various sources of systematic error and allowing an estimate of the sources of random error. The yearly V-band averages of observed sky brightness ranged from 21.287 to 21.906 magnitudes per square arc second. The color of the sky is $B-V$ = 0.930 and does not change discernibly over the course of the sunspot cycle. After correcting the V-band data to the zenith, we find that the airglow component varied a factor of 4.5 over the course of the solar cycle. Once the 11-year solar cycle effect is removed from the data, the most significant contribution to the scatter of individual data points appears to be the short term variations on time scales of tens of minutes like those observed by the Whole Earth Telescope project.
TL;DR: In this article, the authors show that the number of close approaches of asteroids coming from this area to within a minimum distance of less than 0.01 AU of the Earth is more than 30% of the total.
Abstract: The Spaceguard Project proposes to set up a network of five ground-based telescopes, each with an aperture of 2–3 m. With ground-based telescopes, there is a blind celestial area surrounding the Sun (say, within 30 degrees), in which an asteroid approaching the Earth cannot be detected optically because of bright sky background. Our study shows that the number of close approaches of asteroids coming from this area to within a minimum distance of less than 0.01 AU of the Earth is more than 30% of the total.
TL;DR: The recommendations of the Commission Internationale de l'Eclairage regarding sky luminance distribution measurements are reported, along with a survey of measurement techniques used to date, and a detailed description of videography.
Abstract: Daylighting as a key element in quality assessment of the built environment has led to an increasing interest in its corollaries, and in its integration with artificial light sources in interiors. The use of daylighting requires a knowledge of the sky luminance distribution since work plane illuminances and interior surface luminances depend on this. In this paper the recommendations of the Commission Internationale de l'Eclairage regarding sky luminance distribution measurements are reported, along with a survey of measurement techniques used to date. There follows a detailed description of videography, considering the principal system components, and finally some considerations relating to its possible application in this area are discussed.
TL;DR: In this article, an integration of the shadowband exclusion of the sky radiance was made for a range of latitudes, shadow-band dimensions, and sky conditions, and it was shown that the correction factors in the incident photosynthetically active radiation (PAR) are typically smaller than reported in the literature for the entire solar shortwave band.
TL;DR: A novel automated ground-based star-pointing spectrometer system has been constructed for long-term deployment in Antarctica, and some preliminary measurements of ozone from Antarctica are shown.
Abstract: A novel automated ground-based star-pointing spectrometer system has been constructed for long-term deployment in Antarctica. Similar to our earlier stellar system, a two-dimensional detector array measures the spectra of the star and the adjacent sky, so that auroral emission from the sky can be subtracted from the stellar signal. Some new features are an altitude–azimuth pointing mirror, so that the spectrometer does not move; slip rings to provide its power thereby avoiding flexing of cables and restriction of all-around viewing; and a glazed enclosure around the mirror to ensure protection from rain and snow, made from flat plates to avoid changing the focal length of the telescope. The optical system can also view sunlight scattered from the zenith sky. The system automatically points and tracks selected stars and switches to other views on command. The system is now installed at Halley in Antarctica, and some preliminary measurements of ozone from Antarctica are shown.
Journal Article•
TL;DR: In this article, the authors report from follow-up observations of high redshift AGN candidates from the ROSAT All-Sky Survey (RASS) that RX J0911.4+0551 is a gravitationally lensed QSO with z = 2.800.
Abstract: We report from follow-up observations of high redshift AGN candidates from the ROSAT All-Sky Survey (RASS) that RX J0911.4+0551 is a gravitationally lensed QSO with z = 2.800. With an X-ray luminosity of LX = 4 · 1046 ergs s−1 it belongs to the X-ray brightest radio quiet QSOs. However, we must point out that the existing observations do not exclude the possibility that other objects inside the error circle are responsible for the X-ray flux, in particular a lensing cluster. Careful image analysis discerned three optical images. The separation between the two brighter components of 0. ′′80 is below the seeing value during the observations. The fainter component has a distance of 3. ′′1. The spectra of the brighter joint A, B component and the C component show no measurable differences in continuum and absorption lines. Three strong CIV absorption line systems with Wλ(1549) > 1 Å are visible in the spectra. All three have z > 2.3 which makes it improbable that they are caused by the lensing systems. The only spectral difference are larger equivalent widths of the broad emission lines in the brighter QSO components.