Search NASA⌕ Search

SEARCH · Search NASA

Results for “Sky brightness”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

A computer program to determine the possible daily release window for sky target experiments

A computer program is presented which is designed to determine the daily release window for sky target experiments. Factors considered in the program include: (1) target illumination by the sun at release time and during the tracking period; (2) look angle elevation above local horizon from each tracking station to the target; (3) solar depression angle from the local horizon of each tracking station during the experimental period after target release; (4) lunar depression angle from the local horizon of each tracking station during the experimental period after target release; and (5) total sky background brightness as seen from each tracking station while viewing the target. Program output is produced in both graphic and data form. Output data can be plotted for a single calendar month or year. The numerical values used to generate the plots are furnished to permit a more detailed review of the computed daily release windows.

Michaud, N. H.↗
NASA NTRS2004

RXTE All-Sky Slew Survey. Catalog of X-Ray Sources at B Greater Than 10 deg

We report results of a serendipitous hard X-ray (3-20 keV), nearly all-sky (absolute value of b greater than l0 deg.) survey based on RXTE/PCA observations performed during satellite reorientations in 1996-2002. The survey is 80% (90%) complete to a 4(sigma) limiting flux of approx. = 1.8 (2.5) x 10(exp -l1) erg/s sq cm in the 3-20 keV band. The achieved sensitivity in the 3-8 keV and 8-20 keV subbands is similar to and an order of magnitude higher than that of the previously record HEAO-1 A1 and HEAO-1 A4 all-sky surveys, respectively. A combined 7 x 10(exp 3) sq. deg area of the sky is sampled to flux levels below l0(exp -11) erg/ s sq cm (3-20 keV). In total 294 sources are detected and localized to better than 1 deg. 236 (80%) of these can be confidently associated with a known astrophysical object; another 22 likely result from the superposition of 2 or 3 closely located known sources. 35 detected sources remain unidentified, although for 12 of these we report a likely soft X-ray counterpart from the ROSAT all-sky survey bright source catalog. Of the reliably identified sources, 63 have local origin (Milky Way, LMC or SMC), 64 are clusters of galaxies and 100 are active galactic nuclei (AGN). The fact that the unidentified X-ray sources have hard spectra suggests that the majority of them are AGN, including highly obscured ones (N(sub H) greater than l0(exp 23)/sq cm). For the first time we present a log N-log S diagram for extragalactic sources above 4 x l0(exp -12) erg/ s sq cm at 8-20 keV. Key words. cosmo1ogy:observations - diffuse radiation - X-rays general

Revnivtsev, M.↗
NASA NTRS2023

How Dark the Sky: The JWST Backgrounds

We describe the sources of stray light and thermal background that affect JWST observations; report actual backgrounds as measured from commissioning and early science observations; compare those background levels to pre-launch predictions; estimate the impact of the backgrounds on science performance; and explore how the backgrounds probe the achieved configuration of the deployed observatory. We find the observatory is limited by the irreducible astrophysical backgrounds, rather than scattered stray light and thermal self-emission, for all wavelengths λ<12.5 micron, thus meeting the level 1 requirement. This result was not assured given the open architecture and thermal challenges of JWST, and is the result of meticulous attention to stray light and thermal issues in the design, construction, integration, and test phases. From background considerations alone, JWST will require less integration time in the near-infrared compared to a system that just met the stray light requirements; as such, JWST will be even more powerful than expected for deep imaging at 1--5 micron. In the mid-infrared, the measured thermal backgrounds closely match pre-launch predictions. The background near 10 micron is slightly higher than predicted before launch, but the impact on observations is mitigated by the excellent throughput of MIRI, such that instrument sensitivity will be as good as expected pre-launch. These measured background levels are fully compatible with JWST's science goals and the Cycle 1 science program currently underway.

Astronomical instrumentation↗
NASA NTRS2015

When the Sky Falls: Performing Initial Assessments of Bright Atmospheric Events

The 2013 Chelyabinsk super bolide was the first "significant" impact event to occur in the age of social media and 24 hour news. Scientists, used to taking many days or weeks to analyze fireball events, were hard pressed to meet the immediate demands (within hours) for answers from the media, general public, and government officials. Fulfilling these requests forced many researchers to exploit information available from various Internet sources - videos were downloaded from sites like Youtube, geolocated via Google Street View, and quickly analyzed with improvised software; Twitter and Facebook were scoured for eyewitness accounts of the fireball and reports of meteorites. These data, combined with infrasound analyses, enabled a fairly accurate description of the Chelyabinsk event to be formed within a few hours; in particular, any relationship to 2012 DA14 (which passed near Earth later that same day) was eliminated. Results of these analyses were quickly disseminated to members of the NEO community for press conferences and media interviews. Despite a few minor glitches, the rapid initial assessment of Chelyabinsk was a triumph, permitting the timely conveyance of accurate information to the public and the incorporation of social media into fireball analyses. Beginning in 2008, the NASA Meteoroid Environments Office, working in cooperation with Western's Meteor Physics Group, developed processes and software that permit quick characterization - mass, trajectory, and orbital properties - of fireball events. These tools include automated monitoring of Twitter to establish the time of events (the first tweet is usually no more than a few seconds after the fireball), mining of Youtube and all sky camera web archives to locate videos suitable for analyses, use of Google Earth and Street View to geolocate the video locations, and software to determine the fireball trajectory and object orbital parameters, including generation of animations suitable for popular media and presentations. This presentation will give a short description of the characterization procedure and show applications of the tools, which have become vital to answering the question of "What was that bright light in the sky?" in the post-Chelyabinsk, 24/7 news world.

Cooke, William J.↗
NASA NTRS1974

Study of the atmospheric conditions affecting infrared astronomical measurements at White Mountain, California

Measurements are described of atmospheric conditions affecting astronomical observations at White Mountain, California. Measurements were made at more than 1400 times spaced over more than 170 days at the Summit Laboratory and a small number of days at the Barcroft Laboratory. The recorded quantities were ten micron sky noise and precipitable water vapor, plus wet and dry bulb temperatures, wind speed and direction, brightness of the sky near the sun, fisheye lens photographs of the sky, description of cloud cover and other observable parameters, color photographs of air pollution astronomical seeing, and occasional determinations of the visible light brightness of the night sky. Measurements of some of these parameters have been made for over twenty years at the Barcroft and Crooked Creek Laboratories, and statistical analyses were made of them. These results and interpretations are given. The bulk of the collected data are statistically analyzed, and disposition of the detailed data is described. Most of the data are available in machine readable form. A detailed discussion of the techniques proposed for operation at White Mountain is given, showing how to cope with the mountain and climatic problems.

Field, G. B.↗
NASA NTRS2009

MODIS Observations of Enhanced Clear Sky Reflectance Near Clouds

Several recent studies have found that the brightness of clear sky systematically increases near clouds. Understanding this increase is important both for a correct interpretation of observations and for improving our knowledge of aerosol-cloud interactions. However, while the studies suggested several processes to explain the increase, the significance of each process is yet to be determined. This study examines one of the suggested processes three-dimensional (3-D) radiative interactions between clouds and their surroundings by analyzing a large dataset of MODIS (Moderate Resolution Imaging Spectroradiometer) observations over the Northeast Atlantic Ocean. The results indicate that 3-D effects are responsible for a large portion of the observed increase, which extends to about 15 km away from clouds and is stronger (i) at shorter wavelengths (ii) near optically thicker clouds and (iii) near illuminated cloud sides. This implies that it is important to account for 3-D radiative effects in the interpretation of solar reflectance measurements over clear regions in the vicinity of clouds.

Varnai, Tamas↗
NASA NTRS1986

The zodiacal background in the IRAS data

The IRAS sky survey yielded a very extensive picture of bright diffuse thermal emission from interplanetary dust grains at wavelengths from 12 to 100 micrometers. These data provide insights into the character, spatial distribution, and perhaps origin of these particles which both confirm and expand upon those gained from previous zodiacal light studies. The zodiacal emission is a major component of the large scale infrared brightness of the sky at all IRAS wavelengths. It must therefore be carefully characterized both to facilitate study of large-angular-scale sources in the Galaxy and beyond using IRAS data, and to permit optimum design of future space infrared instrument.

Hauser, M. G.↗
NASA NTRSDate not supplied

Seven Years of Bright Meteor Data from the NASA All Sky Fireball Network

The NASA All Sky Fireball Network is a network consisting of 18 all-sky meteor cameras across the continental US. We present a data release of 33,660 bright meteors collected between 2013 and 2019. The released data consists of trajectory, orbit, radiant, shower association, and brightness. We discuss the camera hardware and software used to make the observations, the characteristics of the data, and known error sources. The camera hardware consists of Watec 902H2 Ultimate CCD cameras with a fish-eye lens giving an all-sky field of view. The data is complete until an absolute meteor magnitude of approximately -4, but meteors down to a magnitude of -1 are routinely observed. The cameras are spread across the continental United States in five subnetworks, with each network consisting of two to five cameras. The cameras report to a central server where the data is processed each morning. The network is modeled after the University of Western Ontario’s Southern Ontario Meteor Network. The cameras are running All-sky and Guided Real-time Detection (ASGARD) meteor detection software and analysis pipeline.

Aaron Kingery↗
DOE OSTI2022

The relation between quasars’ optical spectra and variability

Abstract Brightness variation is an essential feature of quasars, but its mechanism and relationship to other physical quantities are not understood well. We aimed to find the relationship between the optical variability and spectral features to reveal the regularity behind the random variation. It is known that a quasar’s Fe ii/Hβ flux ratio and equivalent width of [O iii]5007 are negatively correlated; this is called Eigenvector 1. In this work, we visualized the relationship between the position on this Eigenvector 1 (EV1) plane and how the brightness of the quasars had changed after ∼10 yr. We conducted three analyses, using a different quasar sample in each. The first analysis showed the relation between the quasars’ distributions on the EV1 plane and how much they had changed brightness, using 13438 Sloan Digital Sky Survey quasars. This result shows how brightness changes later are clearly related to the position on the EV1 plane. In the second analysis, we plotted the sources reported as “changing-look quasars” (or “changing-state quasars”) on the EV1 plane. This result shows that the position on the EV1 plane corresponds to the activity level of each source, and the bright or dim states of them are distributed on the opposite sides divided by the typical quasar distribution. In the third analysis, we examined the transition vectors on the EV1 plane using sources with multiple-epoch spectra. This result shows that the brightening and dimming sources move on a similar path and they reach a position corresponding to the opposite activity level. We also found this trend is opposite to the empirical rule that $R_{\rm {Fe\, \small {II}}}$ positively correlated with the Eddington ratio, which has been proposed based on the trends of a large number of quasars. From all these analyses, it is indicated that quasars tend to oscillate between both sides of the distribution ridge on the EV1 plane; each of them corresponds to a dim state and a bright state. This trend in optical variation suggests that significant brightness changes, such as changing-look quasars, are expected to repeat.

Astronomy & Astrophysics↗
NASA NTRS1974

The influence of ozone and aerosols on the brightness and color of the twilight sky

The radiance and color of the twilight sky are calculated for single scattered radiation with the use of spherically symmetric models of the earth's atmosphere. Spherical geometry is used throughout the calculations with no plane-parallel approximations. Refraction effects are taken into account through fine subdivision of the atmosphere into spherical shells of fixed index of refraction. Snell's law of refraction is used to calculate a new direction of travel each time that a photon traverses the interface between layers. Five different models of the atmosphere were used: a pure molecular scattering atmosphere; molecular atmosphere plus ozone absorption; and three models with aerosol concentrations of one, three, and ten times normal together with molecular scattering and ozone absorption. The results of the calculations are shown for various observation positions and local viewing angles in the solar plane for wavelengths in the range from 0.40 to 0.75 micron.

Adams, C. N.↗
NASA NTRS2015

When the Sky Falls NASA's Response to Bright Bolide Events Over Continental USA

Being the only U.S. Government entity charged with monitoring the meteor environment, the Meteoroid Environment Office (MEO) has deployed a network of allsky and wide field meteor cameras, along with the appropriate software tools to quickly analyze data from these systems. However, the coverage of this network is still quite limited, forcing the incorporation of data from other cameras posted to the internet in analyzing many of the fireballs reported by the public and media. Information on these bright events often needs to be reported to NASA Headquarters by noon the following day; thus a procedure has been developed that determines the analysis process for a given fireball event based on the types and amount of data available. The differences between these analysis processes are shown by looking at four meteor events that the MEO responded to, all of which were large enough to produce meteorites.

Blaauw, R. C.↗
DOE OSTI2025

University of Miami G-band Vapor Radiometer Calibration (UMGVR_CAL) Field Campaign Report

Cold-air outbreak (CAO) clouds in the Arctic are commonly mixed-phase (MP); however, the partitioning of the amount of ice and water in CAO clouds and precipitation is not always well observed. Understanding how cloud phases partition as a function of cloud life cycle is important for predicting snowfall rates, convective life cycle, and intensity at weather timescales. The partitioning into liquid versus ice also has radiative impacts that are consequential for climate. These concerns motivated the incorporation of an airborne G-band vapor radiometer (GVR) into an National Science Foundation-supported aircraft campaign named the Cold Air outbreak Experiment in the Sub-Arctic Region (CAESAR). The GVR is an upward-pointing passive microwave radiometer using four frequencies centered around the 183.31 GHz water vapor absorption line, displaced by +- 1, 3, 7, and 14 GHz. For context, The U.S. Department of Energy (DOE)’s Atmospheric Radiation Measurement (ARM) user facility operates a surface-based GVR at its North Slope of Alaska (NSA) site. The same GVR has been used previously for a field campaign in the southeast Pacific, where an offset was noticed between brightness temperatures (Tbs) measured under clear skies compared to those calculated from a radiative transfer model. To account for any calibration offsets to the Tbs, a request was made to DOE to allow the GVR to operate at ARM’s Southern Great Plains (SGP) observatory and enable comparisons between its measurements and those available at SGP. This request was granted, titled ‘UMGVR_CAL’, short for ‘UMGVR_Calibration’. From October 30 to November 10, 2023, the GVR was deployed to the ARM SGP site to take advantage of their regular, nearby radiosonde launches under clear-sky conditions. The latter were determined using the SGP total sky imagery data. The GVR brightness temperatures in these clear-sky conditions were compared to those calculated by a radiative transfer code (PAMTRA) based on the SGP radiosondes. During the campaign, four suitable clear-sky episodes could be used for the GVR calibration. While few in number, these proved to be enough to satisfy our goal.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1985

Capabilities of the GRO/BATSE for monitoring of discrete sources

Although the Burst and Transient Source Experiment (BATSE) to be flown on the Gamma Ray Observatory has as its primary objective the detection of gamma ray bursts, its uncollimated design will enable it to serve a unique function as an all-sky monitor for bright hard X-ray and low-energy gamma ray sources. Pulsating sources may be detected by conventional techniques such as summed-epoch and Fourier analyses. The BATSE will, in addition, be able to use Earth occultation in an unprecedented way to monitor sufficiently bright sources as often as several times per day over approx. 85% of the sky. Estimates of the expected BATSE sensitivity using both of these techniques are presented.

Wilson, R. B.↗
NASA NTRS1989

A rocket-borne measurement of interstellar dust emission at high galactic latitude

The diffuse brightness of the sky was measured in six submillimeter passbands, using a rocket-borne, liquid helium-cooled, absolute radiometer. The average brightness was reported which was observed in each of the passbands, and the dominant source of emission was tentatively identified in the three shortest wavelength bands as interstellar dust (ISD). Spacial structure was observed in these bands, as would be expected for emission from the ISD. The average column density of H I was calculated in each field of view along the scan path. All three bands show a significant correlation with H I. The obtained values are in excellent agreement with those computed for a mixture of graphite and silicate grains. A significant residual emission, not correlated with the H I column density, is evident in all three channels.

Lange, Andrew E.↗
DOE OSTI2025

University of Miami G-band Vapor Radiometer Calibration at SGP during November 2023

From October 13, 2023 until November 16, 2023, the GVR was deployed to the DOE ARM SGP site, to take advantage of their regular near-by radiosonde launches under clear-sky conditions. The latter were determined using the SGP total sky imagery data. The GVR brightness temperatures in these clear-sky conditions were compared to those calculated by a radiative transfer code (PAMTRA) based on the SGP radiosondes. During the campaign, 4 suitable clear-sky episodes occurred that could be used for the GVR calibration. While few in number, these proved to be enough to satisfy our goal.

airborne G-band Vapor Radiometer↗