Showing papers on "Solar eclipse published in 2001"

A Cross-Age Study of Junior High School Students' Conceptions of Basic Astronomy Concepts.

Abstract: Junior high school students' astronomy conceptions were analysed by means of a written questionnaire presented to them during the beginning of the first semester. The main findings were as follows: almost half of the students indicated that the cause of the day-night cycle is the Earth spinning on its axis; most students chose as their best account for changes in the Moon's phases the Moon moving around the Earth. Despite that, most students thought that the Moon must be in its Full phase for there to be a total solar eclipse; most students underestimated the distances in the Universe and overestimated the Earth's diameter. A great proportion of students indicated that the reason for the different seasons is the tilt of the Earth's axis relative to the plane of its orbit as it revolves around the Sun. But almost the same number of students chose the varying distance between Sun and Earth or between the Earth, Moon and Sun, as a reason for the seasons. Only a third of the students answered correctly that i...

Total solar eclipse effects on VLF signals: Observations and modeling

Abstract: During the total solar eclipse observed in Europe on August 11, 1999, measurements were made of the amplitude and phase of four VLF transmitters in the frequency range 16–24 kHz Five receiver sites were set up, and significant variations in phase and amplitude are reported for 17 paths, more than any previously during an eclipse Distances from transmitter to receiver ranged from 90 to 14,510 km, although the majority were 10,000 km Negative phase changes were observed on most paths, independent of path length Although there was significant variation from path to path, the typical changes observed were ∼3 dB and ∼50° The changes observed were modeled using the Long Wave Propagation Capability waveguide code Maximum eclipse effects occurred when the Wait inverse scale height parameter β was 05 km−1 and the effective ionospheric height parameter H′ was 79 km, compared with β=043 km−1 and H′=71 km for normal daytime conditions The resulting changes in modeled amplitude and phase show good agreement with the majority of the observations The modeling undertaken provides an interpretation of why previous estimates of height change during eclipses have shown such a range of values A D region gas-chemistry model was compared with electron concentration estimates inferred from the observations made during the solar eclipse Quiet-day H′ and β parameters were used to define the initial ionospheric profile The gas-chemistry model was then driven only by eclipse-related solar radiation levels The calculated electron concentration values at 77 km altitude throughout the period of the solar eclipse show good agreement with the values determined from observations at all times, which suggests that a linear variation in electron production rate with solar ionizing radiation is reasonable At times of minimum electron concentration the chemical model predicts that the D region profile would be parameterized by the same β and H′ as the LWPC model values, and rocket profiles, during totality and can be considered a validation of the chemical processes defined within the model

Vertical structure of a gravity wave like oscillation in the ionosphere generated by the solar eclipse of August 11, 1999

Abstract: The dependence in altitude and time of the ionospheric electron density and its altitude variations during the solar eclipse of August 11, 1999, have been studied. The true height electron density profiles recorded at the Observatori de l'Ebre station (40.8° N, 0.5° E) during a rapid sequence vertical ionospheric sounding campaign have been used. A gravity wave like oscillation in the ionosphere has been characterized after the maximum of solar occultation by the Moon. The event is clearly seen in both the plasma frequency and in the altitude variations of the F region in the altitude range from 150 to 250 km, and it has a dominant oscillating period T=57.5 min. The oscillation activity linked with the gravity wave event is found to exist in the variations of the ionospheric parameters, being coherent with the oscillations characterized in the plasma frequency variations. The source-origin of the event was located around the transition region between F1 and F2 layers and from that altitude the wave propagates vertically drawing energy upwards and downwards simultaneously. The decreasing/increasing solar ionizing radiation and the cooling/heating processes linked with the solar eclipse are discussed as a possible mechanism to explain the gravity wave event observed in the electron density and dynamics of the ionosphere.

Micrometeorological measurements during the total solar eclipse of August 11, 1999

Abstract: Micrometeorological measurements of radiation, atmospheric and soil parameters, and turbulent energy and momentum e uxes, ozone and carbon dioxide e uxes have been conducted over a maize e eld at FreisingWeihenstephan in Southern Germany during the total solar eclipse on August 11, 1999. For the period 30 minutes before and after the totality the weather conditions at the location where the micrometeorological measurements were made was satisfactory. Several connections between the irradiation and other meteorological parameters over a maize e eld have been found. The time response between irradiation and the long-wave upward radiation was only a few minutes, whereas almost all parameters caused by the turbulent transport had a time shift of up to 30 minutes. A period of nearly 30 minutes with reduced turbulence regime after the totality was found. Using a wavelet transformation for the time series, a change of time scales from longer to shorter ones was observed before the totality, and after the turbulence increased in the short time scales. The investigation of the residuum of the closure of the energy balance showed that with a time shift for the latent heat e ux (unlike the net radiation) after the totality, a better energy budget closure was obtained.

Did the solar eclipse of August 11, 1999, show a geomagnetic effect?

Abstract: The solar eclipse of August 11, 1999, presented good conditions for the study of associated geophysical effects. Ionospheric measurements clearly show a decrease of electron density due to the reduced solar irradiation during the eclipse. However, contrary to claims elsewhere, the decreased conductivity did not cause an obvious effect in the geomagnetic recordings at the Earth's surface. Recordings of several European geomagnetic observatories and of a temporary variometer network, set up specially to observe an eclipse effect in detail, have been studied directly and in terms of equivalent currents in the ionosphere. We present the results of these studies and discuss possible current configurations that might explain the lack of an eclipse effect in geomagnetic recordings.

Impacts of the solar eclipse of 11 August 1999 on routinely recorded meteorological and air quality data in south-west Germany

Abstract: The total solar eclipse of 11 August 1999 over Central Europe was also visible in Baden-Wuerttemberg, a state in south-west Germany. To investigate the impact of the total solar eclipse on the lower planetary boundary layer, meteorological and air quality data extracted from routine measurements at six sites in BadenWuerttemberg were examined. The meteorological data were recorded at the Plittersdorf meteorological station (in the path of totality of the total solar eclipse) and at the Forestmeteorological Site Hartheim (outside the path of totality of the total solar eclipse). The air quality data were obtained from four ofe cial air quality monitoring stations located at Freudenstadt, Karlsruhe-West, Rastatt and Welzheimer Wald, all of which lie within the path of totality of the total solar eclipse. Due to cloudiness, weather conditions on 11 August 1999 were not optimal in south-west Germany. However, the transient reduction (followed by a rise) induced by the total solar eclipse on meteorological variables including global solar radiation, upward longwave radiation, net radiation, air temperature, horizontal wind speed, elevation angle of the three-dimensional wind vector as well as turbulent sensible and latent heat e uxes was quite obvious. Despite unfavourable weather conditions, half-hourly mean values of ozone routinely measured at the above-mentioned standard ofe cial air quality monitoring stations showed a varying decline up to 27% at the urban station Rastatt and 37% at the background station Welzheimer Wald. This decline was owing mainly to the fall in global radiation during the total solar eclipse. However, additional ine uences by advection and deposition can not be precluded. Zusammenfassung

The Effect of the 1999 Total Solar Eclipse on the Ionosphere

Abstract: The localised “night” created as the moon's shadow travelled across the Earth during the total solar eclipse of 11th August 1999, produced changes in the ionosphere across Europe that were monitored with a variety of modern instrumentation. The passage of the 100km wide, super-sonic lunar shadow offered the opportunity to examine the changes in electron densities, radio absorption, neutral wind patterns and the possible generation of waves in the layers of the ionosphere. All these for an event for which the cause of the disturbance can be calculated with accuracy. Reported here are the results from the vertical ionosondes located under the path of totality and in the partial eclipse region and dual frequency GPS TEC measurements. The ionosondes showed that even in the partial shadow the peak electron densities of the F & E ionospheric layers decreased by as much as 20–35%. The TEC measurements showed that the vertical equivalent line integrated electron density dropped by 15% at the 97% partial eclipse north of the path of totality. The consequences of these observations are discussed in relation to making model predictions.

Development of meteorological parameters and total ozone during the total solar eclipse of August 11, 1999

Abstract: During the total eclipse of August 11, 1999 frequent showers occurred due to a unstable stratification of the air mass. At different observation sites, meteorological effects from the eclipse (99.4% coverage at Hohenpeissenberg) and from showers were superimposed making it partly difficult to unambiguously interpret the observations. The weather radar at Hohenpeissenberg observatory provided a general overview of the distribution of clouds and precipitation in this area (200 km diameter). From the Garching site in the zone of totality (100%) temperature and wind data taken on a 50 m mast were evaluated. By selecting periods with relatively low cloud cover it was possible to approximately follow the development of the vertical temperature and wind profiles during the eclipse. The minimum temperature at Hohenpeissenberg (about 450 m above the altitude of Garching) during the eclipse was comparable to that during the previous night, the corresponding value measured at Garching remained about 2 K above the minimum observed during clear sky conditions in the previous night. Showers before, during or after the eclipse may have induced vertical exchange of air parcels. Temperatures during a shower change towards the same direction at all altitudes, thus no inversion forms. Additionally, air parcels with relatively lower concentrations of trace constituents were transported down from aloft for time periods of 10-15 minutes. These mixing processes significantly determined the temporal variations of various trace substances measured during the eclipse. Total ozone measurements at Hohenpeissenberg were performed with both DOBSON and BREWER spectrophotometers and at another site within the zone of totality by using a portable Microtops II filter instrument. Different results were obtained for both sites. These differences can be to a large extend, but not exclusively, attributed to eclipse induced shifts (limb darkening and straylight effects in the atmosphere) in the wavelength pairs used to calculate total ozone. However, there also appeared to be real fluctuations in total ozone during the reemerging phase of the sun which may be related to eclipse induced gravity waves.

MACS for Global Measurement of the Solar Wind Velocity and the Thermal Electron Temperature During the Total Solar Eclipse on 11 August 1999

Abstract: MACS for Multi-Aperture Coronal Spectrometer is a fiber-optic-based spectrograph designed and used to perform global measurement of the solar wind velocity and the thermal electron temperature of the solar corona during the total solar eclipse on 11 August 1999. The motivation for the construction of MACS was provided by the theory formulated by Cram (1976) for the formation of the K-coronal spectrum and a method for determining the radial profile of the thermal electron temperature of the solar corona. Based on this theory a subsequent application was carried out by Ichimoto et al. (1996) using a slit-based spectroscopic study during the total solar eclipse on 3 November 1994. We have modified Cram’s theory to incorporate the role of the solar wind velocity in the formation of the K-corona and have identified wind and temperature sensitive intensity ratios. Instead of a slit-based spectrograph MACS consists of twenty fiber optic tips placed at the focal plane of the telescope and positioned to see different radii and latitudes of the solar corona. Another fiber is placed at the center of the frame and uses the lunar shadow for a measure of the background signal. The other ends of the fibers are vertically aligned and placed at the primary focus of the collimating lens of the spectrograph thus providing simultaneous spectra from all of the fibers. In this first paper (Paper I) we describe our instrument and the obtained coronal spectra. The final and complete results will be presented in Paper II (Reginald and Davila, 2000).

Anomalous gravity data during the 1997 total solar eclipse do not support the hypothesis of gravitational shielding

Abstract: We present arguments that rule out the recent suggestion by Wang et al. that their observations of anomalous gravity data during the 1997 total solar eclipse in China could be evidence for shielding of gravity of the Sun by the Moon, or could be pointing to some new property of gravitation. In fact, we are able to use their stretch of data obtained before and after the eclipse to constrain the characteristic shielding parameter to the lowest bound ever from a terrestrial experiment.

Physical decoupling of the GOES daytime 3.9 µ m channel thermal emission and solar reflection components using total solar eclipse data

Abstract: The spectra of solar and terrestrial emissions are considered largely as being decoupled from one another, such that shortwave (reeectance) and longwave (emissive) radiative properties are often discussed as entirely separate regimes. Instruments having detector pass-bands situated in the region of cross- over near the 3.9mm atmosphericwindow (where solar and thermal emissions are of comparable magnitude), however, detect both solar reeection and thermal emission simultaneously during daytime operation. This poses a problem to daytime cloud retrievals which seek to exploit the unique optical properties of liquid water at these near-infrared wavelengths but require measurementof either the solar or the thermal component exclusively. Without a priori knowledge of these components,empirical relationships or iterative processes must be applied, often without a practical means of quantifying the errors implicit to them. Here, total solar eclipses are proposed as a physical mechanism to decoupling the two radiative components by eŒectively removing the reeected solar radiation from the 3.9mm scene during the eclipse. Considerations for this problem are discussed and comparisons to previous approximations presented.

Boundary layer photochemistry during a total solar eclipse

Abstract: Simultaneous measurements of radiation, photolysis frequencies, O3, CO, OH, PAN and NOx species were carried out in the boundary layer, along with pertinent meteorological parameters, under total solar eclipse conditions. This experiment performed at about 34 solar zenith angle and noontime conditions thus provided a case study about the interactions between radiation and photochemistry under fast “day-night” and “night-day” transitions, at high solar elevation. The results reveal a close correlation of photolysis frequencies jO 1D and jNO2with the UV radiation e ux. All three parameters show, due to the decreasing fraction of direct radiation at shorter wavelengths, much weaker cloud shading effects than global solar radiation. NO and OH concentrations decrease to essentially zero during totality. Subsequently, NO and OH concentrations increased almost symmetrically to their decrease preceding totality. The NO/NO2 ratio was proportional to jNO2 over 30 min before and after totality indicating that the partitioning of NOx species is determined by jNO2. Simple box model simulations show the effect of reduced solar radiation on the photochemical production of O3 and PAN.

The Influence of a solar eclipse on temperature and wind in the Upper-Rhine Valley - A numerical case study

Abstract: The effects on temperature and wind caused by the solar eclipse of August 11, 1999 in the south western part of Germany were simulated While during the real event clouds and precipitation were present in most of the model domain cloud free conditions are assumed for the simulation A temperature decrease of up to 7 K was simulated during the eclipse event close to the surface Thermal stability changes from unstable to stable conditions and the temperature gradient reaches values which are comparable to those normally found after sunset Temperature keeps about 1 K lower after the eclipse event during the rest of the day Boundary layer height shortly after the eclipse event differs by several hundred meters The effects on wind speed are rather small with the exception of the slopes of the mountains and in the vicinity of Lake Constance

Ground-based observation of emission lines from the corona of a red-dwarf star

Abstract: All 'solar-like' stars are surrounded by coronae, which contain magnetically confined plasma at temperatures above 106 K. (Until now, only the Sun's corona could be observed in the optical-as a shimmering envelope during a total solar eclipse.) As the underlying stellar 'surfaces'-the photospheres-are much cooler, some non-radiative process must be responsible for heating the coronae. The heating mechanism is generally thought to be magnetic in origin, but is not yet understood even for the case of the Sun. Ultraviolet emission lines first led to the discovery of the enormous temperature of the Sun's corona, but thermal emission from the coronae of other stars has hitherto been detectable only from space, at X-ray wavelengths. Here we report the detection of emission from highly ionized iron (Fe XIII at 3,388.1 A) in the corona of the red-dwarf star CN Leonis, using a ground-based telescope. The X-ray flux inferred from our data is consistent with previously measured X-ray fluxes, and the non-thermal line width of 18.4 km s-1 indicates great similarities between solar and stellar coronal heating mechanisms. The accessibility and spectral resolution (45,000) of the ground-based instrument are much better than those of X-ray satellites, so a new window to the study of stellar coronae has been opened.

Switching the light off: A break in photosynthesis and sap flow of forest trees under total solar eclipse

Abstract: In mature trees of Picea abies, Fagus sylvatica and Quercus robur, photosynthesis and transpiration were assessed in response to the total solar eclipse that occurred in Central Europe during the late morning hours of August 11, 1999, a day with changing cloudiness. Measurements were conducted at three forest sites located in the totality zone and the 99% area of the eclipse within a radius of about 100 km around the city of Munich (southern Germany). The eclipse lasting 164 minutes lowered the photosynthetic photon flux density (PPFD) to about 1 μmol m -2 s -1 during the 2-minute totality period, when the sky was clear. During totality, photosynthesis was reduced to an extent that allowed CO 2 release to dominate the gas exchange of leaves. Effects on transpiration were less pronounced as the totality was apparently too short to induce distinct stomatal closure in response to low PPFD. Transpiration was strongly reduced, however, by increased air humidity and wet leaf surfaces during sporadic rain showers which preceded or succeeded the eclipse during the same day, whereas low PPFD through intermittent cloudiness during rain only moderately reduced photosynthesis. Although transpiration was lowered to a minor extent only by the eclipse, the latter affected the water transport through the whole tree, as reflected in a decline in the sap flow rate through the basal stem part with a time delay depending on the species. Nevertheless, trees responded in a synchronous way, regardless of the site, species or the percent degree of the eclipse.

The BAYSOFI Campaign - Measurements Carried out during the Total Solar Eclipse of August 11, 1999

Abstract: The total solar eclipse of August 11, 1999 provided a unique opportunity to observe the input of fast day-night and night-day transitions, under high solar elevation around noon, on the earth-atmosphere-biosphere system. Within the interdisciplinary e eld campaign BAYSOFI, measurements of radiation, boundary layer micrometeorology and photochemistry, photosynthesis and transpiration were carried out at Freising-Weihenstephan and several locations nearby focusing on short-term effects of the eclipse. Although the overall grosswetterlage on August 11 was not favourable for viewing the eclipse, with clouds covering most of central Europe, observational conditions at Weihenstephan were fair due to a large hole in the cloud layer which appeared just half hour before totality lasting for more than one hour. Thus signie cant effects of the eclipse on radiation, photolysis rates, OH, the temperature, wind, turbulence structure and stratie cation, ozone and CO 2 e uxes, photosynthesis, transpiration and sap e ow of trees could be observed which are reported and discussed in the following sequence of papers.

European light dosimeter network (ELDONET): 1998 data

Abstract: The European light dosimeter network of over 40 stations has been established in Europe and other continents equipped with three-channel filter dosimeters to measure solar radiation in three channels, UV-B (280–315 nm), UV-A (315–400 nm) and photosynthetically active radiation (PAR). The recorded data have been evaluated, and the monthly doses in all three channels show a strong latitudinal dependence from northern Sweden to the Canary Islands. There are a few remarkable exceptions such as the data recorded at the high mountain station on the Zugspitze (German Alps) and unequal doses at stations at comparable latitudes which indicate the impact of local weather conditions and mean sunshine hours. While generally peak values are recorded in the months of June and July, the UV-B maxima are shifted later into the year, which is due to the antagonistic functions of decreasing solar angles and increasing transparency of the atmosphere as the total column ozone decreases in the second half of the year for the Northern Hemisphere. This is supported by comparison with modelled total column ozone and satellite-based measurements. Also the ratios of UV-B:UV-A and UV-B:PAR as well as UV-A:PAR peak during the summer months, with the exception of the northernmost station at Abisko (north Sweden) where the UV-A:PAR ratio peaks in the winter months which is due to the specific photoclimatic conditions north of the polar circle. The penetration of solar radiation into the water column was found to strongly depend on the transparency of the water column. In Gran Canaria more than 10% of the surface UV-B penetrated to 4–5 m depth. The path of the solar eclipse on 11 August 1999 could be followed in several stations with different degrees of occlusion of the sun disk.

Total Solar Eclipse of 2002 December 04

Abstract: On 2002 December 04, a total eclipse of the Sun will be visible from within a narrow corridor which traverses the Southern Hemisphere The path of the Moon's umbral shadow begins in the South Atlantic, crosses southern Africa and the Indian Ocean, and ends at sunset in southern Australia A partial eclipse will be seen within the much broader path of the Moon's penumbral shadow, which includes the southern two thirds of Africa, Antarctica, Indian Ocean and Australia Detailed predictions for this event are presented and include besselian elements, geographic coordinates of the path of totality, physical ephemeris of the umbra, topocentric limb profile corrections, local circumstances for approximately 400 cities, maps of the eclipse path, weather prospects, the lunar limb profile and the sky during totality Information on safe eclipse viewing and eclipse photography is included

Instantaneous mapping of ionospheric characteristics using 5-minute measurements for the day of the total solar eclipse of 11 August 1999

Abstract: Instantaneous mapping methods for hourly observations were developed within the COST 251 European Action. The hourly maps of foF2 for eclipse day are available on the web page http://www.cbk.waw.pl/rwc/idce.html of the Ionospheric Despatch Centre in Europe. However, the eclipse effect on the ionosphere requires more frequent time scale for the observations than 1 hour. This paper presents the results of maps of foF2, foF1, foE with the use of 5-minute measurements during the eclipse of 11 August 1999. The instantaneous maps are shown be a useful tool to study the effect of the solar eclipse upon the ionosphere.

Einstein, Eddington and the 1919 Eclipse

Abstract: The modern era of cosmology began with the publication of Einstein's general theory of relativity in 1915. The first experimental test of this theory was Eddington's famous expedition to measure the bending of light at a total solar eclipse in 1919. So famous is this experiment, and so dramatic was the impact on Einstein himself, that history tends not to recognize the controversy that surrounded the results at the time. In this paper I discuss the experiment in its historical and sociological context and show that it provides valuable lessons for modern astronomy and cosmology.