SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Eclipse cycle

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The ancient Greek astronomical calculating machine, known as the Antikythera Mechanism, predicted eclipses, based on the 223-lunar month Saros cycle. Eclipses are indicated on a four-turn spiral Saros Dial by glyphs, which describe type and time of eclipse and include alphabetical index letters, referring to solar eclipse inscriptions. These include Index Letter Groups, describing shared eclipse characteristics. The grouping and ordering of the index letters, the organization of the inscriptions and the eclipse times have previously been unsolved. A new reading and interpretation of data from the back plate of the Antikythera Mechanism, including the glyphs, the index letters and the eclipse inscriptions, has resulted in substantial changes to previously published work. Based on these new readings, two arithmetical models are presented here that explain the complete eclipse prediction scheme. The first model solves the glyph distribution, the grouping and anomalous ordering of the index letters and the structure of the inscriptions. It also implies the existence of lost lunar eclipse inscriptions. The second model closely matches the glyph times and explains the four-turn spiral of the Saros Dial. Together, these models imply a surprisingly early epoch for the Antikythera Mechanism. The ancient Greeks built a machine that can predict, for many years ahead, not only eclipses but also a remarkable array of their characteristics, such as directions of obscuration, magnitude, colour, angular diameter of the Moon, relationship with the Moon’s node and eclipse time. It was not entirely accurate, but it was an astonishing achievement for its era.

Concepts: Earth, Moon, Lunar eclipse, Eclipse, Solar eclipse, Saros cycle, Eclipse cycle, Antikythera mechanism

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Solar eclipses provide a rapidly changing solar radiation environment. These changes can be studied using simple photodiode sensors, if the radiation reaching the sensors is unaffected by cloud. Transporting the sensors aloft using standard meteorological instrument packages modified to carry extra sensors, provides one promising but hitherto unexploited possibility for making solar eclipse radiation measurements. For the 20 March 2015 solar eclipse, a coordinated campaign of balloon-carried solar radiation measurements was undertaken from Reading (51.44°N, 0.94°W), Lerwick (60.15°N, 1.13°W) and Reykjavik (64.13°N, 21.90°W), straddling the path of the eclipse. The balloons reached sufficient altitude at the eclipse time for eclipse-induced variations in solar radiation and solar limb darkening to be measured above cloud. Because the sensor platforms were free to swing, techniques have been evaluated to correct the measurements for their changing orientation. In the swing-averaged technique, the mean value across a set of swings was used to approximate the radiation falling on a horizontal surface; in the swing-maximum technique, the direct beam was estimated by assuming that the maximum solar radiation during a swing occurs when the photodiode sensing surface becomes normal to the direction of the solar beam. Both approaches, essentially independent, give values that agree with theoretical expectations for the eclipse-induced radiation changes.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

Concepts: Earth, Sun, Lunar eclipse, Eclipse, Solar eclipse, Saros cycle, Eclipse cycle, Limb darkening

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This article reports on the near-surface atmospheric response at the High Arctic site of Svalbard, latitude 78° N, as a result of abrupt changes in solar insolation during the 20 March 2015 equinox total solar eclipse and notifies the atmospheric science community of the availability of a rare dataset. Svalbard was central in the path of totality, and had completely clear skies. Measurements of shaded air temperature and atmospheric pressure show only weak, if any, responses to the reduced insolation. A minimum in the air temperature at 1.5 m above the ground occurred starting 2 min following the end of totality, though this drop was only slightly beyond the observed variability for the midday period. Eclipse-produced variations in surface pressure, if present, were less than 0.3 hPa.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

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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

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A wide range of surface and near-surface meteorological observations were made at the University of Reading’s Atmospheric Observatory in central southern England (latitude 51.441° N, longitude 0.938° W, altitude 66 m above mean sea level) during the deep partial eclipse on the morning of 20 March 2015. Observations of temperature, humidity, radiation, wind speed and direction, and atmospheric pressure were made by computerized logging equipment at 1 Hz, supplemented by an automated cloud base recorder sampling at 1 min intervals and a high-resolution (approx. 10 m vertical interval) atmospheric sounding by radiosonde launched from the same location during the eclipse. Sources and details of each instrumental measurement are described briefly, followed by a summary of observed and derived measurements by meteorological parameter. Atmospheric boundary layer responses to the solar eclipse were muted owing to the heavily overcast conditions which prevailed at the observing location, but instrumental records of the event documented a large (approx. 80%) reduction in global solar radiation, a fall in air temperature of around 0.6°C, a decrease in cloud base height, and a slight increase in atmospheric stability during the eclipse. Changes in surface atmospheric moisture content and barometric pressure were largely insignificant during the event.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

Concepts: Earth, Lunar eclipse, Atmospheric pressure, Atmosphere, Eclipse, Ecliptic, Solar eclipse, Eclipse cycle

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The National Eclipse Weather Experiment (NEWEx) was a citizen science project for atmospheric data collection from the partial solar eclipse of 20 March 20. Its role as a tool for schools outreach is discussed here, in seeking to bridge the gap between self-identification with the role of a scientist and engagement with science, technology, engineering and mathematics subjects. (The science data generated have had other uses beyond this, explored elsewhere.) We describe the design of webforms for weather data collection, and the use of several external partners for the dissemination of the project nationwide. We estimate that up to 3500 pupils and teachers took part in this experiment, through the 127 schools postcodes identified in the data submission. Further analysis revealed that 43.3% of the schools were primary schools and 35.4% were secondary. In total, 96.3% of participants reported themselves as ‘captivated’ or ‘inspired’ by NEWEx. We also found that 60% of the schools that took part in the experiment lie within the highest quintiles of engagement with higher education, which emphasizes the need for the scientific community to be creative when using citizen science projects to target hard-to-reach audiences.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

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

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Solar retinopathy refers to damage to the central macula caused by exposure to intense solar radiation, most frequently observed after a solar eclipse.

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

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Eclipse retinopathy is a condition with macular damage resulting from viewing of a solar eclipse. This case report illustrates how eclipse retinopathy was diagnosed with a delay of more than 30 years. The report also summarises how solar eclipse can be observed without risk of retinal damage.

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

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On the cover: “Solar eclipse? Wait a second, am I in the right Journal?” the reader might ask after seeing the cover of this issue of Cytometry Part A. No reason to worry, you are in the right place. The current cover image is just a stunningly beautiful figment of the artist’s imagination based on the study reporting a simple, efficient, and semiquantitative method for estimating cellular SiO2 nanoparticle (NP) contents. This approach may not only decipher the fundamental cell-NP interaction mechanisms, but also lead to improved nanotoxicity assay methods. Read the accompanying article by Choi and coworkers in this issue. Cover design by Bärbel Beran [www.beran-design.de].

Concepts: Assay, Lunar eclipse, The Current, The Reader, Eclipse, Solar eclipse, Eclipse cycle