Absolute Brightness (review)

2008 ◽  
Vol 61 (8) ◽  
pp. 341-341
Author(s):  
April. Spisak
Keyword(s):  
Absolute Brightness

scholarly journals Evidence for Physical Aging of Periodic Comets

1989 ◽  
Vol 116 (1) ◽  
pp. 607-628
Author(s):  
L. Kresák
Keyword(s):  
Survival Time ◽  
Physical Aging ◽  
Planetary System ◽  
Observational Evidence ◽  
Statistical Evidence ◽  
Cometary Nuclei ◽  
Aging Rate ◽  
Statistical Effect ◽  
Total Disappearance ◽  
Absolute Brightness

AbstractObservational evidence for the aging processes in periodic comets is reviewed. This includes progressive changes of the comets’ absolute brightness, sudden destructive events (outbursts and splitting of cometary nuclei), temporary intermissions in activity, total disappearance, and existence of asteroidal objects moving in cometary orbits. Indirect statistical evidence is provided by the equilibrium between the aging rate and the net injection of comets into the inner planetary system. All of this information is consistent with typical active lifetimes of 200 to 500 revolutions at small perihelion distances (q < 3 AU). The active lifetimes are sometimes intermitted by dormant periods, which tend to occur especially during the latest phases of evolution. Splits and outbursts do not seem to have a decisive statistical effect on the survival time. Some periodic comets evolve into inactive asteroid-like objects, but the question of whether these still contain some supply of volatiles, and thus can renew their activity, remains open.

scholarly journals Absolute brightness measurements at the LURE synchrotron with a bolometer and application to the absolute calibration of photodiodes and photocathodes

1994 ◽  
Vol 12 (3) ◽  
pp. 573-583 ◽  
Author(s):  
C. Reverdin ◽  
P. Troussel ◽  
F. Le Guern ◽  
J.L. Bourgade ◽  
D. Schirmann ◽  
...  
Keyword(s):  
Low Noise ◽  
Beam Line ◽  
Absolute Calibration ◽  
Density Measurements ◽  
X Ray ◽  
Laser Plasma Interaction ◽  
Absolute Measurements ◽  
Power Densities ◽  
Adequate Data ◽  
Absolute Brightness

An electrically calibrated bolometer designed to measure VUV and soft X-ray radiation in tokamaks was installed at the end of the calibration beam line used by CEL-V at the LURE synchrotron. Low-noise electronics and an adequate data acquisition enabled absolute measurements of power densities as low as 1 μW/cm2. Power density measurements are presented. At the same location several soft X-ray detectors used in laser-plasma interaction studies were installed and their absolute calibration was performed (photocathodes, photodiodes, etc.). Calibration results are presented and compared with a Henke model for photocathode response.

scholarly journals Measurement of Solar Absolute Brightness Temperature Using a Ground-Based Multichannel Microwave Radiometer

2021 ◽  
Vol 13 (15) ◽  
pp. 2968
Author(s):  
Lianfa Lei ◽  
Zhenhui Wang ◽  
Yingying Ma ◽  
Lei Zhu ◽  
Jiang Qin ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Brightness Temperature ◽  
Microwave Radiation ◽  
Atmospheric Temperature ◽  
Solar Observation ◽  
The Sun ◽  
Temperature And Humidity ◽  
Microwave Radiometers ◽  
Humidity Profiles ◽  
Absolute Brightness

Ground-based multichannel microwave radiometers (GMRs) can observe the atmospheric microwave radiation brightness temperature at K-bands and V-bands and provide atmospheric temperature and humidity profiles with a relatively high temporal resolution. Currently, microwave radiometers are operated in many countries to observe the atmospheric temperature and humidity profiles. However, a theoretical analysis showed that a radiometer can be used to observe solar radiation. In this work, we improved the control algorithm and software of the antenna servo control system of the GMR so that it could track and observe the sun and we use this upgraded GMR to observe solar microwave radiation. During the observation, the GMR accurately tracked the sun and responded to the variation in solar radiation. Furthermore, we studied the feasibility for application of the GMR to measure the absolute brightness temperature (TB) of the sun. The results from the solar observation data at 22.235, 26.235, and 30.000 GHz showed that the GMR could accurately measure the TB of the sun. The derived solar TB measurements were 9950 ± 334, 10,351 ± 370, and 9217 ± 375 K at three frequencies. In a comparison with previous studies, we obtained average percentage deviations of 9.1%, 5.3%, and 4.5% at 22.235, 26.235, and 30.0 GHz, respectively. The results demonstrated that the TB of the sun retrieved from the GMR agreed well with the previous results in the literature. In addition, we also found that the GMR responded to the variation in sunspots and a positive relationship existed between the solar TB and the sunspot number. According to these results, it was demonstrated that the solar observation technique can broaden the field usage of GMR.

scholarly journals Superassociations in distant galaxies

1964 ◽  
Vol 20 ◽  
pp. 122-126 ◽  
Author(s):  
V. A. Ambartsumian
Keyword(s):  
Special Class ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Photographic Images ◽  
Large Complex ◽  
Distant Galaxies ◽  
Absolute Brightness ◽  
30 Doradus

It is well known that the Large Magellanic Cloud contains in addition to a considerable number of ordinary O-associations a certain number of large objects which, however, are similar in nature to the associations. These objects were named “constellations” by Shapley. But the large complex 30 Doradus surpasses notably all of these objects both in diameter and in absolute brightness. The latter is of the order of −15m0 while its diameter is of the order of 600 pc. If we take the average absolute brightness of associations in our Galaxy as equal to −10m0 then it turns out that 30 Doradus is 100 times more luminous than the ordinary associations. The photographic images of more distant galaxies reveal that sometimes complexes occur in them of the same order of luminosity and dimensions as 30 Doradus. Therefore it seems to us useful to regard these complexes as a special class of objects and call them superassociations.

G0 Revisited as Equally Bright Reference Boundary

2021 ◽  
Vol 2021 (29) ◽  
pp. 247-252
Author(s):  
Hao Xie ◽  
Mark D. Fairchild
Keyword(s):  
Color Appearance ◽  
Color Patch ◽  
Paired Comparisons ◽  
Chromaticity Diagram ◽  
Color Science ◽  
Appearance Models ◽  
Absolute Brightness

Brilliance and zero grayness (denoted as G0) and are two terms coined by Ralph Evans. Nayatani, Heckaman and Fairchild have done series of work to incorporate them into comprehensive color appearance models. In this work, those concepts were reexamined to scale lightness/brightness across the chromaticity diagram. Specifically, observers, mostly with a color science background, were asked to adjust the luminance of a color patch to appear with no grayness, or equivalently just about/cease to glow. The hypothesis was that lightness can be equalized across those chromaticities and the Helmholtz-Kohlrausch effect is automatically incorporated. This hypothesis was verified in a follow-up experiment where another group of observers completed paired comparisons of the brightness between the collected G0 results. The G0 task was also repeated under another two levels of adaption backgrounds, based on which different absolute brightness results for a given chromaticity might be derived. In addition, high correlations between the G0 results (as a perceptual boundary between appearance modes) and different physical gamut boundaries including MacAdam's optimal colors were found for possible computational proxies and ecologically meaningful implications.

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