Solar eclipse

About: Solar eclipse is a research topic. Over the lifetime, 2737 publications have been published within this topic receiving 22625 citations.

Hipparchus on the distances of the sun and moon

Abstract: "Hipparchus' investigation of this topic is based principally on the sun. For since it is a consequence of certain other properties of the sun and moon (which we shall discuss below) that when the distance of one of the luminaries is given that of the other is also determined, he tries to demonstrate the distance of the moon by guessing the distance of the sun. He first assumes that the sun has only the least perceptible parallax, in order to find its distance, and afterwards uses the solar eclipse which he adduces. At one time he assumes that the sun has no perceptible parallax, at another that it has a significant [ixavov] parallax : as a result the ratios of the moon's distance [to the earth's radius] came out different for him for each of the hypotheses he set out. For in the case of the sun it is quite uncertain not merely how great a parallax it has, but whether it has any at all".

Sky color near the horizon during a total solar eclipse

Abstract: A theory for the color of the sky near the horizon for an observer in the umbral region of a total solar eclipse is presented. The model uses a Rayleigh scattering atmosphere, and the light reaching the observer is a beam of singly scattered sunlight, which, in turn, has suffered depletion by scattering in its passage from outside the shadow region. The model predicts both the red color observed in the lowest 8° of the sky for the total solar eclipse of 30 June 1973 and the enriched blue color of the sky at any elevation angle greater than the solar elevation angle. The model is also adapted to explain the reddening of the horizon sky observed during such times as when a dark cloud passes overhead or when the light from a large city is seen from the distance at night.

The earliest known solar eclipse record redated

Abstract: AN astronomical event recorded on a clay tablet found in 1948 among the ruins of the ancient city of Ugarit, in what is now Syria, was identified 20 years ago as a description of a total solar eclipse that occurred on 3 May 1375 BC1,2. The dating of ancient solar eclipses provides reference points to fix the long-term evolution of angular momentum in the Earth-Moon system3. We have reanalysed the Ugarit eclipse record4. A new historical dating of the tablet, and mention in the text of the visibility of the planet Mars during the eclipse as well as the month in which it occurred enables us to show that the recorded eclipse in fact occurred on 5 March 1223 BC. This new date implies that the secular deceleration of the Earth's rotation has changed very little during the past 3,000 years.

Ionospheric response over Europe during the solar eclipse of March 20, 2015

Abstract: The solar eclipse on March 20, 2015 was a fascinating event for people in Northern Europe. From a scientific point of view, the solar eclipse can be considered as an in situ experiment on the Earth’s upper atmosphere with a well-defined switching off and on of solar irradiation. Due to the strong changes in solar radiation during the eclipse, dynamic processes were initiated in the atmosphere and ionosphere causing a measurable impact, for example, on temperature and ionization. We analyzed the behavior of total ionospheric ionization over Europe by reconstructing total electron content (TEC) maps and differential TEC maps. Investigating the large depletion zone around the shadow spot, we found a TEC reduction of up to 6 TEC units, i.e., the total plasma depletion reached up to about 50%. However, the March 20, 2015 eclipse occurred during the recovery phase of a strong geomagnetic storm and the ionosphere was still perturbed and depleted. Therefore, the unusual high depletion is due to the negative bias of up to 20% already observed over Northern Europe before the eclipse occurred. After removing the negative storm effect, the eclipse-induced depletion amounts to about 30%, which is in agreement with previous observations. During the solar eclipse, ionospheric plasma redistribution processes significantly affected the shape of the electron density profile, which is seen in the equivalent slab thickness derived by combining vertical incidence sounding (VS) and TEC measurements. We found enhanced slab thickness values revealing, on the one hand, an increased width of the ionosphere around the maximum phase and, on the other, evidence for delayed depletion of the topside ionosphere. Additionally, we investigated very low frequency (VLF) signal strength measurements and found immediate amplitude changes due to ionization loss at the lower ionosphere during the eclipse time. We found that the magnitude of TEC depletion is linearly dependent on the Sun’s obscuration function. By modelling TEC depletion and knowing the Sun’s obscuration function in advance, Global Navigation Satellite System (GNSS) operators may improve the broadcast ionospheric correction during a solar eclipse day.

Neutral points of skylight polarization observed during the total eclipse on 11 August 1999

Abstract: We report here on the observation of unpolarized (neutral) points in the sky during the total solar eclipse on 11 August 1999. Near the zenith a neutral point was observed at 450 nm at two different points of time during totality. Around this celestial point the distribution of the angle of polarization was heterogeneous: The electric field vectors on the one side were approximately perpendicular to those on the other side. At another moment of totality, near the zenith a local minimum of the degree of linear polarization occurred at 550 nm. Near the antisolar meridian, at a low elevation another two neutral points occurred at 450 nm at a certain moment during totality. Approximately at the position of these neutral points, at another moment of totality a local minimum of the degree of polarization occurred at 550 nm, whereas at 450 nm a neutral point was observed, around which the angle-of-polarization pattern was homogeneous: The electric field vectors were approximately horizontal on both sides of the neutral point.