Showing papers on "Sky published in 1988"
TL;DR: In this paper, a technique for obtaining CCD photometry of a large ensemble of stars, with precision limited by atmospheric scintillation and photon statistics, was presented, under bright-sky conditions with a 0.9m telescope.
Abstract: A technique for obtaining CCD photometry of a large ensemble of stars, with precision limited by atmospheric scintillation and photon statistics is presented. Under bright-sky conditions with a 0.9-m telescope, a precision of about 0.0015 mag relative to an ensemble average standard was obtained for 12th-13th mag stars in M 67 with exposure times of 1 min. The increase in noise level due to variable cirrus clouds is minimal. Effective noise levels for the detection of coherent oscillations with periods of 5-20 min could thus be reduced to about 30 micromag over ten nights of observing for stars of this brightness. A much larger ensemble of faint stars could be followed at lower precision with sky background and photon statistics as dominant error sources. Four probable-cluster DA white dwarfs were detected in the old galactic cluster M 67, using B, V calibration photometry.
98 citations
TL;DR: In this article, the average angular distribution of short wavelength sky radiance for clear, partly cloudy, and overcast sky conditions has been measured for the range of solar zenith angle 31° to 80°.
96 citations
TL;DR: In this paper, the authors used 3D scans of the clear sky short wavelength (0.3-3.0 μm) radiance to produce sky radiance contour maps for solar zenith angles 32° to 80°.
77 citations
TL;DR: In this paper, an all-sky map of IR-excess gas has been produced by subtracting the H I component from the IR brightness, and the large IR excess residuals that are spatially connected are used to define IR excess clouds.
Abstract: An all-sky map of IR-excess gas has been produced by subtracting the H I component from the IR brightness. The large IR-excess residuals that are spatially connected are used to define IR-excess clouds. Also, nearby molecular clouds at high Galactic latitude and clouds with local heating sources or a larger dust-to-gas ratio than average are identified. The map and a catalog of 516 significant clouds are presented and statistically analyzed.
70 citations
TL;DR: A catalog of 248 small molecular clouds selected from the northern hemisphere Palomar Observatory Sky Survey has been assembled as discussed by the authors, and coordinates accurate to 0.5 arcmin, optical extents and orientation angles and cross-references are given for all of the clouds.
Abstract: A catalog of 248 small molecular clouds selected from the northern hemisphere Palomar Observatory Sky Survey has been assembled. These clouds have angular sizes of less than 10 arcmin (the mean of the sample is 4 arcmin), are reasonably well-isolated, and centrally opaque. They most closely resemble small versions of the larger Bok globules and Barnard objects. Many (30%) of the smallest members of this catalog have not been previously cataloged or studied. Coordinates accurate to 0.5 arcmin, optical extents and orientation angles, and cross-references are given for all of the clouds. Radial velocities, obtained from CO observations, are listed for 158 of the clouds. Additionally, 339 associated or possibly associated IRAS point sources are listed for 147 of the clouds. As most of these clouds have few or no foreground stars and subtend small angular extents, they are likely the smallest (all < 1.5 pc) and simplest dark molecular clouds near the Sun. The mean ellipticity (b) of the clouds in the catalog is 2.0, indicating that spherical cloud models may not be appropriate for this sample. The mean orientations, with respect to the galactic plane, of the clouds showing ellipticities greater than unity has no angular dependence; that is, the local galactic plane does not seem to order the direction of the optically determined ellipticity for the clouds. The far-infrared properties of the clouds with associated IRAS sources are similar to those seen in the sample of dark cloud cores studied by Beichman et al. (1986) [Ap. J., 307, 337], but are somewhat cooler (19 K vs 28 K for the means) and less FIR bright. Millimeter 12CO (J = 2-1) observations of the centers of 93 of the cataloged clouds shows that most (70%) of the sample are cool (gas kinetic temperature ∼8 K) and quiescent (gas dynamical motions ≈ sonic). Some clouds exhibit warmer gas temperatures possibly driven by radiative heating from nearby stars. Another small group of clouds exhibit the cool temperatures and supersonic linewidths characteristic of active embedded protostellar collapse or outflow.
47 citations
TL;DR: In this paper, the brightness of the zenith sky decreases exponentially by about 0.4 mag in both V and B photometric bands during at least the first half of the night, and the results indicate that the level of solar EUV flux and the time of night must be taken into account when assessing the quality of a dark-sky site.
Abstract: Measurements performed at San Benito Mountain during 1976-87 reveal that the zenith sky brightness in the V and B photometric bands is well correlated with the solar 10.7-cm radio flux, and thus with the intensity of the solar EUV radiation in the 100-625 A range. It is found that the brightness of the zenith sky decreases exponentially by about 0.4 mag in both V and B during at least the first half of the night. The results indicate that the level of solar EUV flux and the time of night must be taken into account when assessing the quality of a dark-sky site.
42 citations
Journal Article•
36 citations
TL;DR: In this article, a detailed analysis of 1438 all-sky scans of shortwave radiance (95 skypoints per scan) for overcast skies shows that angular dependence of the (suitably normalized) diffuse sky radiance can be represented by the analytical expression.
01 Mar 1988
TL;DR: In this paper, an extremely simple, low cost very low frequency radio telescope is proposed, consisting of a large array of short wires laid on the lunar surface, each wire equipped with an amplifier and a digitizer, and connected to a common computer.
Abstract: Because of terrestrial ionospheric absorption, very little is known of the radio sky beyond 10 m wavelength. An extremely simple, low cost very low frequency radio telescope is proposed, consisting of a large array of short wires laid on the lunar surface, each wire equipped with an amplifier and a digitizer, and connected to a common computer. The telescope could do simultaneous multifrequency observations of much of the visible sky with high resolution in the 10 to 100 m wavelength range, and with lower resolution in the 100 to 1000 m range. It would explore structure and spectra of galactic and extragalactic point sources, objects, and clouds, and would produce detailed quasi-three-dimensional mapping of interstellar matter within several thousand parsecs of the Sun.
TL;DR: In this article, a model referred to as the cloudy sky geometry (CSG) model is proposed for the description of the geometric characteristics of clouds in the sky, where clouds are modeled on a modification of the parallel relationships among upright vertical cylinders of variable diameter and height.
TL;DR: It was found that the single scattering approximation is applicable for detection of stratospheric aerosols by twilight measurement during background periods and a scheme is proposed for retrieving the stratospolic scattering coefficient utilizing the measured degree of polarization at the 0.7-microm wavelength in the zenith direction of the twilight sky.
Abstract: A backward Monte Carlo computation procedure has been used to simulate the intensity and degree of polarization of the twilight sky during 1977. It was found that the single scattering approximation is applicable for detection of stratospheric aerosols by twilight measurement during background periods. Based on the simulation, a scheme is proposed for retrieving the stratospheric aerosol scattering coefficient utilizing the measured degree of polarization at the 0.7-μm wavelength in the zenith direction of the twilight sky. Compared with the in situ measurement, both the retrieved total optical depth and the retrieved profile of the aerosol scattering coefficient below 30 km agree reasonably well with measurements.
Book•
01 Jun 1988
TL;DR: In this paper, a book called the new patterns in the sky myths and legends of the stars is ordered and the book is sent directly to the customer after purchasing. But why should you wait for some days to get or receive the book?
Abstract: Why should wait for some days to get or receive the the new patterns in the sky myths and legends of the stars book that you order? Why should you take it if you can get the faster one? You can find the same book that you order right here. This is it the book that you can receive directly after purchasing. This the new patterns in the sky myths and legends of the stars is well known book in the world, of course many people will try to own it. Why don't you become the first? Still confused with the way?
TL;DR: In separate conversations, Ross, Holt, Turrell, and Saad-Cook as mentioned in this paper discuss their monumental-scale works involving natural phenomena, which are at various stages of completion, ranging from preparatory stages to works already completed.
Abstract: In separate conversations, four artists discuss their monumental-scale works involving natural phenomena. The projects of Charles Ross, Nancy Holt, James Turrell and Janet Saad-Cook are at various stages of completion, ranging from preparatory stages to works already completed. The artists speak about their own creative process and about their personal vision for their art.
TL;DR: In this paper, a three-component (isotropic, circumsolar and horizonbrightening) model of the angular distribution of sky radiance has been tested and validated against a data base of measured sky radiances.
Abstract: A three‐component (isotropic, circumsolar and horizon‐brightening) model of the angular distribution of sky (short‐wave) radiance has been tested and validated against a data base of measured sky radiance. The data base encompasses cloud cover 0.0 to 1.0 and solar zenith angles 30 to 80°. Empirical constants have been derived for the model enabling the prediction of sky radiances for any sky condition.
01 Jan 1988
TL;DR: In this article, the authors used the Three Discrete Radiance Components (TDRC) model for the instantaneous and time-averaged distribution of diffuse sky radiance for the case of cumulus clouds, using a limited set of data.
Abstract: The Three Discrete Radiance Components (TDRC) model, which was introduced by the authors as a model for the instantaneous and time-averaged distribution of diffuse sky radiance, is calibrated for the case of cumulus clouds, using a limited set of data The TDRC model incorporates the Cloudy Sky Geometry (CSG) model, a model proposed by the authors for the distribution of clouds across the sky dome in which clouds are modelled as upright vertical cylinders of variable diameter and height, and in which the distribution of clouds is modelled as cylinders randomly spaced, but having an average separation distance in any azimuthal direction A validation of the calibrated TDRC model is performed, in which predictions of the model are compared with luminance observations, for a wide range of cloudiness This comparison showed good agreement It is anticipated that the proposed model will be of significance to researchers in several fields, particularily those in solar engineering
01 Jan 1988
TL;DR: In this article, a model referred to as the Cloudy Sky Geometry (CSG) model is proposed for the description of the geometric characteristics of cloudy skies, where clouds are modelled as upright vertical cylinders of variable diameter and height, and the distribution of clouds in the sky is modeled as cylinders randomly spaced, but having an average separation distance in any azimuthal direction.
Abstract: A model, referred to as the Cloudy Sky Geometry (CSG) model, is proposed for the description of the geometric characteristics of cloudy skies. Clouds are modelled as upright vertical cylinders of variable diameter and height, and the distribution of clouds in the sky is modelled as cylinders randomly spaced, but having an average separation distance in any azimuthal direction. Mathematical expressions are derived for the time fraction during which a given point in the sky is either clear or cloudy (including information on what portion of the cloud is visible), and the relationship is developed between cloud amount and average cloud separation distance. A calibration of the model for cumulus clouds is discussed. Although applicable to many disciplines, it is anticipated that the proposed model will be of most importance to solar energy engineering. The authors have integrated the present model into the Three Discrete Radiance Components (TDRC) model, proposed by the authors for the prediction of the instantaneous and time-averaged distribution of diffuse sky radiance.
01 Jan 1988
TL;DR: In this article, a comparison between radiance calculations using the single scattering, additive layer approach and those using a multiple scattering version of the low-level layer approach was made to evaluate the applicability of the multiple scattering approach in the far infrared region.
Abstract: : Measurements of 8- to 12-micrometer near-horizon sky radiances and meteorological parameters over the ocean near San Diego, California were used to evaluate the sky radiance algorithm of LOWTRAN 6. Discrepancies in measured and calculated sky radiances previously attributed to the neglect of multiple scattering effects of aerosols can be overcome by introducing additional low-level layers in the calculations of LOWTRAN 6. A comparison between radiance calculations using the single scattering, additive-layer approach and those using a multiple scattering version of LOWTRAN 6 raises questions about the applicability of the multiple scattering approach in the far infrared region. Keywords: Atmospheric model layering; Infrared sky radiance.
01 Jan 1988
TL;DR: In this paper, large-scale CO surveys of the entire Galactic plane and specific nearby clouds have been combined to produce a panorama of the whole Milky Way in molecular clouds at an angular resolution of 1/2°.
Abstract: Large-scale CO surveys of the entire Galactic plane and specific nearby clouds have been combined to produce a panorama of the entire Milky Way in molecular clouds at an angular resolution of 1/2°. Covering 10°–20° in latitude at all longitudes and all large, nearby clouds at higher latitude, the composite survey is the only molecular line survey to date with sky coverage and resolution comparable to that of the early 21 cm surveys.
01 Jan 1988
TL;DR: In this paper, a linear relationship between the mean and the standard deviation of the sky diffuse radiance is proposed, which is an extension to real skies of the theoretical relationship in the case of single scattering in very clear skies.
Abstract: Based on data collected in Toronto (Canada), some statistical properties of the sky diffuse radiance are investigated. Specifically, a linear relationship between the mean and the standard deviation is proposed. This is an extension to real skies of the theoretical relationship in the case of single scattering in very clear skies. The results may help in developing a more complete understanding of the statistical distribution functions for diffuse sky radiance.
TL;DR: In this paper, an extensive study on certain optical characteristics of the sunlit sky at Seville was carried out from March 1980 to September 1984 by observing two points in the sun's vertical plane: the zenith and the point situated at each instant at 90° to the sun.
TL;DR: In this paper, an alternative to Tregenza's recent scanning pattern for sky photometry is presented and discussed, and an alternative scanning pattern is proposed for sky-photometry.
Abstract: An alternative to Tregenza's recent scanning pattern for sky photometry is presented and discussed.
Patent•
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23 Mar 1988
TL;DR: In this paper, the authors present an easy, multi-using instrument for teaching, navigation, travelling, mapping, archaeology, and astronomical amateurs, which can be also used for direction identification, time service, spot location, concersion of various equations of time.
Abstract: It consists of celestial, time, terrestial, positional disk and solar system isolated from celestial sphere etc. They are connected with axel pins. The demonstration not only explains the law of celestial body's motion clearly but also lets people know astronomical phenomena, including position and motion of the sun, the moon and the planets in stellar sky directly. It can be also used for direction identification, time service, spot location, concersion of various equations of time. Changing with different years' sky atlas, different years' astronomical phenomena will be unfolded before our eyes. It is an easy, multi-using instrument for teaching, navigation, travelling, mapping, archaeology and astronomical amateurs.
01 Jul 1988
TL;DR: The Moonwatch program uses amateur astronomers to obtain a wide range of naked-eye sightings of the new moon to test a mathematical model for predicting first visibilty as discussed by the authors, which takes physical effects such as brightness of the twilight sky, clarity of the atmosphere at the observing site, and the physiology of the human eye into account.
Abstract: The Moonwatch program using amateur astronomers to obtain a wide range of naked-eye sightings of the new moon to test a mathematical model for predicting first visibilty of the new moon is discussed. The algorithm takes physical effects such as brightness of the twilight sky, clarity of the atmosphere at the observing site, and the physiology of the human eye into account. A 1987 test of visibility prediction obtained poor results due to weather conditions. Observers across North and Central America, the Caribbean, and northern South America are asked to record information about the time and location where they first see the crescent of the new moon appear on the horizon.