Showing papers on "Sky published in 1973"

The spectral sensitivity of polarized light orientation inCataglyphis bicolor (Formicidae, Hymenoptera)

Abstract: 1. The desert ant,Cataglyphis bicolor, is able to orient towards the pattern of polarized light in the sky even without perceiving information on the sun's position. The accuracy of artificially induced homing courses is not influenced by performing the experiments just before sunrise and after sunset or by shading the sun. 2. However, after destroying the polarization pattern by appropriate filtering of the skylight (Figs. 1 and 2) the azimuth of the sun was found to be sufficient when working as an isolated orientation parameter (Fig. 5). No influence of the sun's altitude could be shown by mirror experiments (Fig. 6b). 3. By artificially shifting the sun's azimuth either during the foraging or during the return run the sun's azimuth competes with the polarization pattern. In that situation the sun has no influence on direction finding (Fig. 6a and b). 4. The ants tested beneath various colour folios working as large sized spectral filters do not show any direction finding capacities as soon as wavelengths shorter than 410 nm are cut off (Fig. 7). This holds irrespective of whether the sun is visible or not. The accuracy of the homing courses is totally restored by means of an edge filter transmitting in the range λ λ 390 nm (Fig. 9). 5. The results strongly support the hypothesis that only the uv.-receptors are involved in polarization analysis.

Infrared Photography of OH Airglow Structures

Abstract: Results of high-angular-resolution photography of the complex airglow structures present in the infrared sky. The photographs obtained all show bright cloud-like structures which moved on the sky and varied in brightness. It is concluded that these structures are due to varying airglow emission and not to any type of modulation of a uniform background by atmospheric clouds, dust, or haze. It is also concluded that observations of a bright spot from two widely separated sites will yield parallax determinations of the height of the OH emitting layer, so that it is no longer necessary to rely on infrequent rocket measurements at a few places.

An all-sky catalogue of strong radio sources at 408 MHz

Abstract: A catalogue of 160 extragalactic radio sources stronger than 10 f.u. at 408 MHz has been compiled by selecting sources from the Parkes and 3CR surveys but adopting the most accurate values of flux density that are available. The sky coverage of 10·1 sr omits only the galactic plane and Magellanic Cloud regions. The flux density scale due to Wyllie has been used throughout.

Automatic Cloud Cover Indicator System.

Abstract: A method for developing and constructing a cloud cover indicator system is described. The method involves pointing an IR radiometer vertically downward to a movable mirror and measuring the reflected sky radiation by comparing the difference in thermal radiance between clouds and the sky. To determine cloud cover it is only important to have a threshold value for the clear sky. A value for the coverage is produced by a sunning system summation of all signal lengths of one cycle.

Special effect generator for a simulator visual system

Abstract: A system for generating sky, horizon scenes and scenes simulating low visibility in a flight simulator visual system using a television display is shown. Aircraft attitude information is used in a horizon generator to locate the horizon on a line-to-line basis. The information from the horizon generator is modified by functions of visibility range, altitude, time of day and location above or below clouds to develop the proper scenes, such as white for sky below clouds, white for clouds, the blue for sky above clouds and to switch between these synthetically generated scenes and a terrain scene provided by a camera model system or other image generator.

Observations of zodiacal light from the Pioneer 10 Asteroid-Jupiter probe - Preliminary results.

Abstract: The imaging photopolarimeter on the Pioneer 10 Asteroid-Jupiter probe is being used to measure starlight and zodiacal light during the cruise phase of the mission. The 2.5-cm-diam telescope is used with a 2.3 deg field of view to spin/scan the sky in the region between 10 and 151 deg from the direction of motion of the spacecraft. Orthogonal components of brightness are measured in two wavelength bands: blue (3900 to 5000 A) and red (5950 to 7200 A). The gegenschein was observed on Mar. 14, 1972, when the earth-sun-spacecraft angle was 3.4 deg and the spacecraft was 9.2 million km from the earth and 1.011 AU from the sun. The distribution of brightness relative to the antisolar point is similar to that obtained from ground-based observations. Taken together, these results show that the gegenschein is not associated with the earth.

136-MHz/400-MHz radio-sky maps

Abstract: A radio-sky map, covering the whole celestial sphere, is helpful for determining the system noise temperature of an earth-based satellite receiving system. Detailed sky maps for the 136- and 400-MHz space research (space-to-earth) satellite frequency bands have been generated, using a computer, by the National Aeronautics and Space Administration (NASA).

Spectrophotometric Measurements of Noctilucent Clouds

Abstract: Near infrared spectra of a NLC display are compared with spectra from the normal twilight sky for the regions 7850 to 9000 A and 2.8 to 4.2 μ showing that NLC's are scatterers of solar radiation. A...

Dust, Star, and Hydrogen Distributions in the Orion Association

Abstract: From the star counts on the Palomar Sky Survey prints, dust and star distributions in the Orion Association are studied. The Hydrogen distribution in the same region is obtained from an H α photograph. It is found that a considerable part of the interstellar absorption on the line of sight is due to the circumstellar dust grains in the Orion Association.

Mariner 9 ultraviolet spectrometer experiment - Measurements of the Lyman alpha sky background

Abstract: During the flight of Mariner 9 to Mars, the ultraviolet spectrometer on board the spacecraft measured the L-alpha intensity for several points in the sky. These data are compared with a sky map obtained by OGO-5 and the observations of Mariner 6. The absolute calibration of Mariner 9 and Mariner 6 differ by a factor of 1.43 at L-alpha. The low values of the sky brightness measured by Mariner 9 near the sky minimum suggest that the nearby interstellar medium has a kinetic temperature of 200-1100 K and a relative velocity with respect to the sun in the range 13-14 km/sec.

From Day to Twilight to Night

Abstract: Life on planet Earth is tuned to the diurnal drama of day-twilight-night-dawn-day. As Earth rotates within the sunlight sheath, the outward-looking observer notes changes of brightness which cover many powers of ten. The day sky, in the absence of clouds, appears as a blue vault resulting from the scattering of sunlight by the atmospheric components. The brightness of the sky decreases rapidly after sunset as the solar rays illuminate only the higher regions of the atmosphere above the observer. At a solar depression of 18° (end of astronomical twilight) the amount of illuminated atmosphere has become so small that the scattered sunlight is trivial and the night sky can be observed without twilight competition (Figure 1-1).

The hemispheric reflectance of a plane water surface for atmospheric radiation

Abstract: The hemispheric reflectance of a plane water surface is computed for clear sky and low overcast sky emission spectra. The gross features of clear sky emission are described by a model that has a deficiency of emission in the 8- to 13-micron band. The deficiency is most pronounced in the zenith but disappears as the zenith angle approaches the horizon. The radiation from a low overcast sky is assumed to be blackbody. The computation is made using Fresnel formulas for a conducting medium. The hemispheric reflectance for clear sky radiation is found to be approximately 0.018 higher than the overcast (blackbody) value, which ranged from 0.113 to 0.107 for atmospheric temperatures ranging from 273 to 313 K, respectively.

Luminosity functions for k giant stars derived from the two-micron sky survey

Abstract: Description of a method for determining either the space density or the luminosity function from star counts covering large areas of sky. Space density is assumed to vary only in the direction perpendicular to the galactic plane. The method extends that derived for use with the star counts in the Selected Areas by allowing for an integration over a wide and continuous range of galactic latitudes, and is therefore applicable to surveys where the number of stars per square degree is small but the area surveyed is an appreciable fraction of the sky. The catalog (IRC) produced from the 2-micron sky survey at Caltech is such a survey. Application of the method to a selection of IRC stars dominated by K giants shows that if these stars obey Oort's determination of their normalized space density perpendicular to the galactic plane than the dispersion of their 2.2-micron luminosity distribution must be large - i.e., on the order of plus or minus 1.0 min within a single spectral subtype. This result is in accord with conclusions recently set forth by Jung (1970).

A determination of the daytime thermospheric wind profile by observing a lithium trail with a field-of-view scanner

Abstract: A description is given of the design of an instrument which has been built to detect the lithium 671 nm line against the daytime sky continuum. The instrument covers the field of view by means of a servocontrolled scanning mirror and detects the lithium l

Dust-Scattered Starlight - The Diffuse Galactic Light

Abstract: Integrated starlight, zodiacal light, and nightglow - which have been discussed to this point - are the major contributors to the terrestrial night sky light. The resolution of the total light into its principal components is much facilitated by the fact that each has a specific region of concentration in the sky, such concentration being apparent even to the unaided eye.