SciCombinator

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Concept: Eclipse

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There is a fascinating tradition of depicting solar eclipses in Western art, although these representations have changed over time. Eclipses have often been an important feature of Christian iconography, but valued as much for their biblical significance as for the splendour of the physical event. However, as Western culture passed through the Renaissance and Enlightenment the depictions of eclipses came to reflect new astronomical knowledge and a thirst for rational learning well beyond the confines of the church and other elites. Artists also played a surprisingly important role in helping scientists in the nineteenth century understand and record the full phenomena of an eclipse, even as the advent of photography also came to solve a number of scientific puzzles. In the most recent century, artists have responded to eclipses with symbolism, abstraction and playfulness.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

Concepts: Earth, Culture, Europe, Lunar eclipse, Western culture, Renaissance, Eclipse, Solar eclipse

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The eclipses of certain types of binary millisecond pulsars (i.e. ‘black widows’ and ‘redbacks’) are often studied using high-time-resolution, ‘beamformed’ radio observations. However, they may also be detected in images generated from interferometric data. As part of a larger imaging project to characterize the variable and transient sky at radio frequencies <200 MHz, we have blindly detected the redback system PSR J2215+5135 as a variable source of interest with the Low-Frequency Array (LOFAR). Using observations with cadences of two weeks - six months, we find preliminary evidence that the eclipse duration is frequency dependent (∝ν(-0.4)), such that the pulsar is eclipsed for longer at lower frequencies, in broad agreement with beamformed studies of other similar sources. Furthermore, the detection of the eclipses in imaging data suggests an eclipsing medium that absorbs the pulsed emission, rather than scattering it. Our study is also a demonstration of the prospects of finding pulsars in wide-field imaging surveys with the current generation of low-frequency radio telescopes.

Concepts: Frequency, Binary star, Eclipse, Neutron star, Pulsar, Millisecond pulsar, PSR B1257+12, X-ray pulsar

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A camera obscura-type viewer based on pinhole optics, with the apertures being the holes in a commercial snack biscuit (or cracker), produces interesting and easily obtainable projected images, as demonstrated during the 2017 solar eclipse.

Concepts: Book of Optics, Photography, Photographic lens, Eclipse, F-number, Shen Kuo, Pinhole camera, Solar eclipse

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Background: To avoid inconvenience to patients due to linear accelerator down time in busy radio-therapy departments, treatment plans can be switched between linear accelerators provided that all exhibit the same same dosimetric characteristics. In other words linear accelerators should be beam-matched. Aim: The aim of this study was to evaluate the clinical significance of beam-matching using VMAT plans. Materials and Methods: Dosimetric data with a 6MV beam from am Clinac 2100CD were taken as baseline values and other two units, a 2300CD and a Unique Performance, were factory tuned in accordance. An analysis of PDD data was performed for different field sizes to evaluate energy matching. Beam profiles for field sizes of 10×10 cm2 and 40 × 40 cm2 at depths of 1.5 cm and 10 cm were analyzed. The relative output factor and MLC dosimetric properties were compared with each machine to determine variability among the different models. Thirty patients from our database were selected, ten each for head and neck, thorax and pelvis sites. VMAT plans were created in the Eclipse treatment planning system for a Clinac 2100 CD for reference. and verification plans were created for each to compare point dose measurements. Results: The TPR 20/10 for 10 × 10 cm2 was well matched, showing no energy differences. Deviation of all point dose measurements fell within ±3%. Planar dose maps all showed greater than 95% of points with a passed area γ-value less than 1. Conclusion: Our study evaluation of beam matching with treatment planning modeling showed good agreement fior 6 MV beams across all three linear accelerators used in our clinical environment.

Concepts: Head and neck anatomy, Thorax, Particle accelerator, Planning, Match, Eclipse, Linear particle accelerator

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To systematically analyze and present the properties of a small-field, double-scattering proton beam line intended to be used for the treatment of ocular cancer, and to provide configuration data for commission of the Eclipse Ocular Proton Planning System.

Concepts: Proton therapy, Proton, Eclipse, Zoning

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Unprotected and prolonged exposure to ultraviolet (UV) light from sunlight, lasers, and arc welding leads to outer retinal damage. The photoreceptors and retinal pigment epithelium located in the posterior pole are particularly susceptible to this radiation. Classically known as solar retinopathy, this disorder frequently affects young individuals who have clear lenses and a propensity toward observing solar eclipses. Various imaging techniques aid the clinician in diagnosis, even if patients cannot recall an exposure event. By far the most utilized technique is optical coherence tomography, which, in tandem with fluorescein angiography, and fundus autoflourescence, is crucial in ruling out other conditions. Fortunately, the prognosis of acute UV retinopathy is favorable, as most cases fully recover; however, a significant percentage of patients suffer from chronic sequelae: reduced acuity and lifelong central/paracentral scotomas. Thus, education towards understanding UV exposure risks, coupled with either abstinence or proper eye protection, is critical in preventing macular damage. We outline the various etiologies responsible for UV induced retinopathy, describe the limited treatments available, and provide recommendations to minimize the potential devastating ophthalmic consequences as our society increases its reliance on UV-emitting technology and further engages in solar eclipse viewing.

Concepts: Ultraviolet, Sun, Sunlight, Retina, Eye, Ophthalmology, Eclipse, Solar eclipse

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Measurements of atmospheric electrical and standard meteorological parameters were made at coastal and inland sites in southern England during the 20 March 2015 partial solar eclipse. Clear evidence of a reduction in air temperature resulting from the eclipse was found at both locations, despite one of them being overcast during the entire eclipse. The reduction in temperature was expected to affect the near-surface electric field (potential gradient (PG)) through a reduction in turbulent transfer of space charge. No such effect could be unambiguously confirmed, however, with variability in PG and air-Earth current during the eclipse being comparable to pre- and post-eclipse conditions. The already low solar radiation for this latitude, season and time of day was likely to have contributed to the reduced effect of the eclipse on atmospheric electricity through boundary layer stability. The absence of a reduction in mean PG shortly after time of maximum solar obscuration, as observed during eclipses at lower geomagnetic latitude, implied that there was no significant change in atmospheric ionization from cosmic rays above background variability. This finding was suggested to be due to the relative importance of cosmic rays of solar and galactic origin at geomagnetic mid-latitudes.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

Concepts: Earth, Sun, Lunar eclipse, Mercury, Eclipse, Ecliptic, Solar eclipse, Saros cycle

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The behaviour of remotely sensed land surface temperatures (LSTs) from the spinning-enhanced visible and infrared imager (SEVIRI) during the total solar eclipse of 20 March 2015 is analysed over Europe. LST is found to drop by up to several degrees Celcius during the eclipse, with the minimum LST occurring just after the eclipse mid-point (median=+1.5 min). The drop in LST is typically larger than the drop in near-surface air temperatures reported elsewhere, and correlates with solar obscuration (r=-0.47; larger obscuration = larger LST drop), eclipse duration (r=-0.62; longer duration = larger LST drop) and time (r=+0.37; earlier eclipse = larger LST drop). Locally, the LST drop is also correlated with vegetation (up to r=+0.6), with smaller LST drops occurring over more vegetated surfaces. The LSTs at locations near the coast and at higher elevation are also less affected by the eclipse. This study covers the largest area and uses the most observations of eclipse-induced surface temperature drops to date, and is the first full characterization of satellite LST during an eclipse (known to the author). The methods described could be applied to Geostationary Operational Environmental Satellite (GOES) LST data over North America during the August 2017 total solar eclipse.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

Concepts: Earth, Temperature, Lunar eclipse, Celsius, Absolute zero, Thermodynamic temperature, Eclipse, Solar eclipse

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Near-surface air temperature (NSAT) anomalies during the 20 March 2015 solar eclipse are investigated at 266 UK sites, using operational data. The high density of observing sites, together with the wide range of ambient meteorological conditions, provided an unprecedented opportunity for analysis of the spatial variability of NSAT anomalies under relatively uniform eclipse conditions. Anomalies ranged from -0.03°C to -4.23°C (median -1.02°C). The maximum (negative) anomaly lagged the maximum obscuration by 15 min on average. Cloud cover impacted strongly on NSAT anomalies, with larger anomalies in clear-sky situations (p<0.0001). Weaker, but statistically significant, correlations were found with wind speed (larger anomalies in weaker winds), proximity to coast (larger anomalies at inland sites), topography (larger anomalies in topographical low points) and land cover (larger anomalies over vegetated surfaces). In this mid-morning eclipse, the topographical influences on NSAT anomalies were apparently dominated by variations in residual nocturnal inversion strength, as suggested by significant correlations between post-sunrise temperature and NSAT anomaly at clear-sky sites (larger negative anomalies with lower post-sunrise temperatures). The largest NSAT anomaly occurred at a coastal site where flow transitioned from onshore to offshore during the eclipse, in a situation with large coastal temperature gradients associated with antecedent nocturnal cooling.This article is part of the themed issue 'Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse'.

Concepts: Earth, Temperature, Lunar eclipse, Eclipse, Solar eclipse, Saros cycle, Eclipse cycle, Eclipses

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This article reviews atmospheric changes associated with 44 solar eclipses, beginning with the first quantitative results available, from 1834 (earlier qualitative accounts also exist). Eclipse meteorology attracted relatively few publications until the total solar eclipse of 16 February 1980, with the 11 August 1999 eclipse producing the most papers. Eclipses passing over populated areas such as Europe, China and India now regularly attract scientific attention, whereas atmospheric measurements of eclipses at remote locations remain rare. Many measurements and models have been used to exploit the uniquely predictable solar forcing provided by an eclipse. In this paper, we compile the available publications and review a subset of them chosen on the basis of importance and novelty. Beyond the obvious reduction in incoming solar radiation, atmospheric cooling from eclipses can induce dynamical changes. Observations and meteorological modelling provide evidence for the generation of a local eclipse circulation that may be the origin of the ‘eclipse wind’. Gravity waves set up by the eclipse can, in principle, be detected as atmospheric pressure fluctuations, though theoretical predictions are limited, and many of the data are inconclusive. Eclipse events providing important early insights into the ionization of the upper atmosphere are also briefly reviewed.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

Concepts: Earth, Sun, Lunar eclipse, Mercury, Eclipse, Solar eclipse, Saros cycle, Eclipse cycle