Showing papers on "Solar eclipse published in 2009"

The Sun Recorded Through History

Abstract: Preface.- The Sun.- The Solar Structure.- The Photosphere.- Observing the Solar Surface.- The Chromosphere.- The Corona.- The Solar Wind.- 3-D Topology of the Magnetic Field.- Observing the Outer Layers.- Time Scales of Solar Variability.- Solar Terrestrial Relations.- Naked-eye Sunspots.- The Human Eye as a Detector of Light.- Visibility Criteria.- Naked-eye Sunspot Observations.- Naked-eye Sunspots and Temporal Evolution of Solar Activity.- Solar Drawings.- Pretelescopic Instruments.- The Invention of the Telescope.- First Telescopic Observations of Sunspots.- The Maunder Minimum.- The Rise of Solar Activity and the Dalton Minimum: 18th and 19th Centuries.- Sunspots Drawings in the Photography Era.- The First Granulation Drawings.- Sunspot Fine Structures.- Faculae.- White-light Flares.- The Outer Layers of the Sun.- The Influence of the Eye in Solar Drawings.- Physics from Drawings.- Modern Solar Drawings.- Solar Eclipses.- The Basics of Solar Eclipses.- Historical Solar Eclipse Observations.- Science Using Early Reports of Solar Eclipses.- The Solar Diameter and the Astronomical Unit.- The Earth's Orbit.- Measuring the Known World.- Observing Methods of Solar Diameter.- Theoretical Background.- Long-term Variations.- Planetary Transits.- Terrestrial Aurorae and Solar-Terrestrial Relations.- Auroral Physics in Brief.- Folklore, Omen and Myths.- Reports During the Last Two Millennia.- The Search for the Cause.- Catalogues of Aurorae Observations.- Aurorae and Secular Solar Activity.- Aurora and Great Space Weather Events.- Reconstruction of Solar Activity During the Telescopic Era.- Wolf's Reconstruction.- The Reconstruction by Hoyt and Schatten.- Improving and Finding Lost Observations.- Final Comments.- Index.

Latitudinal dependence of the ionospheric response to solar eclipses

Abstract: [1] In this study, we statistically analyze the latitudinal dependence of F2-layer peak electron densities (NmF2) and total electron content (TEC) responses to solar eclipses by using the ionosonde observations during 15 eclipse events from 1973 to 2006 and the GPS TEC observations during six solar eclipse events from 1999 to 2006. We carried out a model study on the latitudinal dependence of eclipse effects on the ionosphere by running a theoretical ionospheric model with the total eclipse occurring at 13 latitudes from 0 Nt o 60N at intervals of 5. Both the observations and simulations show that the NmF2 and TEC responses have the same latitudinal dependence: the eclipse effects on NmF2 and TEC are smaller at low latitudes than at middle latitudes; at the middle latitudes (>40), the eclipse effect decreases with increasing latitude. The simulations show that the smaller NmF2 responses at low latitudes are mainly because of much higher heights of hmF2 at low latitudes and electron density response decreasing rapidly with increasing height. For the eclipse effects at the middle latitudes (>40), the simulations show that the smaller NmF2 or TEC response at higher latitude is mainly ascribed to the larger downward diffusion flux induced by the larger dip angle at this region, which can partly make up for the plasma loss and alleviate the depression of electron density in the F region. The simulated results show that there is an overall decrease in electron temperature throughout the entire height range at the middle latitude, but for the low latitudes the eclipse effect on electron temperature is much smaller at high heights, which is mainly because of the much smaller reduction of photoelectron production rate at its conjugate low heights where only a partial eclipse with small eclipse magnitude occurs.

Phase correlation method for the alignment of total solar eclipse images

Abstract: A modified phase correlation method, based on Fourier transform, which enables the alignment of solar coronal images taken during the total solar eclipses, is presented. The method enables the measurement of translation, rotation, and scaling factor between two images. With the application of this technique, pairs of images with different exposure times, different brightness scale, such as linear for CCD and nonlinear for images taken with photographic film, and even images from different emission lines can be aligned with sub-pixel precision.

The ionospheric behavior in conjugate hemispheres during the 3 October 2005 solar eclipse

Abstract: . We investigate the ionospheric behavior in conjugate hemispheres during the 3 October 2005 solar eclipse, on the basis of observations of electron temperature (Te) from the Defense Meteorological Satellites Program (DMSP) spacecraft, F2 layer critical frequency (foF2) and F2 layer peak height (hmF2) at the Grahamstown ionosonde station, and total electron content (TEC) from the Global Positioning System (GPS) station SUTH. The observations show that when the eclipse occurred in the Northern Hemisphere, there was a decrease in Te, an increase in foF2 and TEC, and an uprising in hmF2 in its conjugate region compared with their reference values. We also simulated the ionosphere behavior during this eclipse using a mid- and low-latitude ionospheric model. The simulations agree well with the observations. Because of the eclipse effect, there are far fewer photoelectrons travelling along the magnetic field lines from the eclipse region to the conjugate region, resulting in reduced photoelectron heating in the conjugate hemisphere which causes a drop in electron temperature and subsequent disturbances in the region.

The ionospheric behavior in conjugate hemispheres during the

Abstract: We investigate the ionospheric behavior in conju- gate hemispheres during the 3 October 2005 solar eclipse, on the basis of observations of electron temperature (Te) from the Defense Meteorological Satellites Program (DMSP) spacecraft, F2 layer critical frequency ( foF2) and F2 layer peak height (hmF2) at the Grahamstown ionosonde station, and total electron content (TEC) from the Global Position- ing System (GPS) station SUTH. The observations show that when the eclipse occurred in the Northern Hemisphere, there was a decrease in Te, an increase in foF2 and TEC, and an uprising in hmF2 in its conjugate region compared with their reference values. We also simulated the ionosphere behav- ior during this eclipse using a mid- and low-latitude iono- spheric model. The simulations agree well with the observa- tions. Because of the eclipse effect, there are far fewer pho- toelectrons travelling along the magnetic field lines from the eclipse region to the conjugate region, resulting in reduced photoelectron heating in the conjugate hemisphere which causes a drop in electron temperature and subsequent dis- turbances in the region.

Scientific observations at total solar eclipses

Abstract: The occasion of the longest totality of an eclipse in the 18 yr 11⅓ d saros cycle leads to taking stock of the scientific value of ground-based eclipse observations in this space age. Though a number of space satellites from the U.S., Europe, Japan, and Russia study the Sun, scientists at eclipses can observe the solar chromosphere and corona at higher spatial resolution, at higher temporal resolution, and at higher spectral resolution than are possible aloft. Furthermore, eclipse expeditions can transport a wide variety of state-of-the-art equipment to the path of totality. Thus, for at least some years to come, solar eclipse observations will remain both scientifically valuable and cost-effective ways to study the outer solar atmosphere.

Total solar eclipse over Antarctica on 23 November 2003 and its effects on the atmosphere and snow near the ice sheet surface at Dome Fuji

Abstract: [1] The Moon cast a long shadow over Antarctica on 23 November 2003 in a total solar eclipse. The eclipse was observed at Dome Fuji Station, located at the highest point of East Dronning Maud Land, Antarctica, and lasted 1 h 41 min 37 s in a cloudless condition, during which the Sun was completely obscured for 1 min 43 s. This was the first total solar eclipse to be observed in the Antarctic ice sheet. During the eclipse at Dome Fuji, the air temperature at 1.5 m above the snow surface and the subsurface snow temperature decreased by 3.0 K and 1.8 K, respectively. Estimated surface snow temperatures decreased by 4.6 K. Atmospheric pressure and wind direction did not change, but the wind speed possibly decreased by 0.3 m/s with decreasing air temperature; natural variations in wind speed before and after the eclipse made it difficult to identify a true effect of the solar eclipse. Variations of energy components (net shortwave and longwave radiations, sensible and latent heat fluxes, and geothermal heat) during the eclipse were investigated. The total loss of global solar radiation during the eclipse was 0.60 MJ m−2, equaling 1.6% of the total daily global solar radiation. Regional effects of the eclipse due to a reduction of global solar radiation for air temperature and snow temperature ranged from 0.015 to 0.020 K (W m−2)−1. We additionally examined the relation between eclipse obscuration (the fraction of the Sun's surface area occulted by the Moon) and the reduction of global solar radiation from the first to second contacts. The eclipse was also observed from space by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard NASA's Terra and Aqua satellites. The observational results of this study will contribute to detailed model calculations for clarifying the meteorological effects of eclipses.

Electron-Temperature Maps of the Low Solar Corona: ISCORE Results from the Total Solar Eclipse of 29 March 2006 in Libya

Abstract: We conducted an experiment in conjunction with the total solar eclipse of 29 March 2006 in Libya that measured the coronal intensity through two filters centered at 3850 A and 4100 A with bandwidths of ≈ 40 A. The purpose of these measurements was to obtain the intensity ratio through these two filters to determine the electron temperature. The instrument, Imaging Spectrograph of Coronal Electrons (ISCORE), consisted of an eight inch, f/10 Schmidt Cassegrain telescope with a thermoelectrically-cooled CCD camera at the focal plane. Results show electron temperatures of 105 K close to the limb to 3×106 K at 1.3R ⊙. We describe this novel technique, and we compare our results to other relevant measurements. This technique could be easily implemented on a space-based platform using a coronagraph to produce global maps of the electron temperature of the solar corona.

Solar eclipse-induced E-region plasma irregularities observed by the Gadanki radar

Abstract: [1] We investigate the generation of low latitude E-region plasma density irregularities that were triggered during a solar eclipse on 11 August 1999. The observations were made using the Gadanki radar. The present study shows that a solar eclipse can provide night-like ionospheric conditions which allow the excitation of plasma instabilities and the generation of irregularities in the E-region at multiple height regions, as happens routinely during post-sunset hours. We surmise that the echo layers were associated with long-lived metallic ion layers that were made manifest when the more abundant ordinary molecular ions disappeared through recombination in the absence of photoionization. We propose that the layers turned unstable via the gradient-drift instability mechanism. This is the first time that a solar eclipse has been conclusively shown to generate E-region plasma irregularities.

Mid-latitude solar eclipses and their influence on ionospheric current systems

Abstract: . Using CHAMP magnetic field data we study the behaviour of the geomagnetic field during two mid latitude eclipses on 21 June 2001 and 22 September 2006. The possible influence of the eclipses on different ionospheric current systems, as seen in the magnetic field measured by CHAMP, is discussed. It is expected that the blocking of solar radiation during an eclipse causes a reduction of the ionospheric conductivity and therefore has an effect on the different current systems. We address in particular the effects of the eclipses on the inter-hemispheric field-aligned currents and on the Sq current system. The two events studied occur under different seasonal conditions, e.g. June solstice and September equinox, therefore quite different aspects can be investigated. We find that the eclipses might affect the direction and intensity of the inter-hemispheric currents and possibly influence the direction of zonal winds, therefore changing the direction of the prevailing F-region dynamo currents. The eclipse in the Southern Hemisphere during September equinox caused inter-hemispheric currents similar to those observed in northern summer. Reverse inter-hemispheric currents were recorded after the end of the eclipse. A large variety of atypical currents was observed during the June event. Most of them might be related to a reversed F-region dynamo in the morning sector and an enhanced conductivity difference between the hemispheres. The eclipse in the south seems to enhance the June solstice conditions considerably.

Linear polarization of flash spectrum observed from a total solar eclipse in 2008

Abstract: We measured linear polarization signals of the flash spectrum ranging from 502.5 nm to 528.5 nm after second contact of a total solar eclipse which occurred on 2008 August 1 in China. A large group of spectral lines (especially those lines produced by neutral iron, neutral copper, and as carbon molecules) are found with very high polarization degrees relative to the continuum polarization, and the linear polarization spectrum is more abundantly structured than the flash spectrum itself. According to the observational result, we conclude that coherent scattering and scattering geometry as well as other mechanisms may together play a very important role in producing the high polarization amplitudes. This will help us deepen our understanding of the physical conditions of the solar upper atmospheres and the physical processes occurring there.

Solar Radius Determination from Total Solar Eclipse Observations on 29 March 2006

Abstract: Solar diameter measurements have been made nearly continuously through different techniques for more than three centuries. They were obtained mainly with ground-based instruments except for some recent estimates deduced from space observations. One of the main problems in such space data analysis is that, up to now, it has been difficult to obtain an absolute value owing to the absence of an internally calibrated system. Eclipse observations provide a unique opportunity to give an absolute angular scale to the measurements, leading to an absolute value of the solar diameter. However, the problem is complicated by the Moon limb, which presents asphericity because of the mountains. We present a determination of the solar diameter derived from the total solar eclipse observation in Turkey and Egypt on 29 March 2006. We found that the solar radius carried back to 1 AU was 959.22±0.04 arcsec at the time of the observations. The inspection of the compiled 19 modern eclipses data, with solar activity, shows that the radius changes are nonhomologous, an effect that may explain the discrepancies found in ground-based measurements and implies the role of the shallow subsurface layers (leptocline) of the Sun.

The role of the 40 foot Schaeberle camera in the Lick Observatory investigations of the solar corona

Abstract: The thesis will present the total solar eclipse expeditions of the Lick Observatory that occurred during the late nineteenth century and continued through the first quarter of the twentieth century. At this period in time, astronomical research centers worldwide, were sending solar eclipse expeditions afar, often under arduous travel and living conditions. The primary goal, of the Lick Observatory’s eclipse expeditions, was to collect photographs and spectrograms of the features of the Sun that can only be seen and recorded in the brief moments of a total solar eclipse of the Sun. The scientific focus of this thesis is the Observatory’s study of the solar corona using large scale photographic images. A summary will be given of the science of the solar corona, as it developed through the midlate nineteenth century up to the period of the Lick Observatory’s eclipse expeditions, which began in 1889. It was then that the corona was on an ever-increasing scale being subjected to scientific analysis with the new tools of photography and the spectroscope. This review will define those contributions made by the study of drawings and photographs of the solar corona up to the time of the Observatory’s expeditions. This will set the stage for the pioneering photography and coronal research conducted by the Lick Observatory, made possible with the development of a new eclipse camera by Staff Astronomer J.M. Schaeberle. Schaeberle, would in turn use its images in his continued analysis of a new theory regarding the forces within the solar corona that define its structure and form. Schaeberle’s unique 40 foot focal length camera will be presented in detail. This instrument was designed for the sole purpose of making large-scale coronal images at a total eclipse of the Sun. These images would reveal fine structure within the corona never seen before. The individual components, making up this camera, will be described with attention given to the care and precision by which they were manufactured, set up, and operated. The Camera will be described at each eclipse site along with pertinent photographic processes. A brief summary of the plate results will be included. A general description of each of the Observatory’s eclipse expeditions will be detailed. The site geographic specifics, staff and volunteers in attendance, individual duties of the members of the eclipse party, layout of the eclipse camp, range of scientific apparatus and their purpose, interaction with local organizations, and any special circumstances that affected the outcome of the expedition’s success or failure are included. The Observatory’s contributions to the knowledge of coronal physics will be presented and subjected to critical analysis. Schaeberle’s new coronal theory based solely on Newtonian mechanics will be reviewed and compared to the concurrent mechanical, magnetic and electric coronal theories, then under study by other prominent astronomers at other institutions. Any connections of the new theory with regard to particle makeup, meteor streams, comets, or gas content of the solar corona, will be mentioned. The resulting scientific output generated from the Schaeberle Camera’s coronal images will then be fitted within the overall knowledge of the solar corona at that point in history. Major coronal research conducted by J.A. Miller of the Sproul Observatory at Swarthmore College using the Lick’s large scale plates will be mentioned as it was an extension in part of the original Schaeberle Mechanical Theory of the Solar Corona. A brief survey of the Lick Observatory involvement of a test of Einstein’s Theory of General Relativity will be presented as it was the principal focus of three of the eclipse expeditions and the Lick Observatory was a chief participant in this paradigm shift of our knowledge of physics. The coronal imaging program of the Observatory will be compared with that of other institutions at individual eclipse dates. This comparison will include a summary of the cameras used for producing large scale images of the corona by all parties. The Lick Observatory’s solar eclipse program will be discussed in terms of its place in the overall scheme of the general research program of the Observatory. In the same manner, the direct photographic eclipse program will be assigned its level of importance on each of the expeditions when compared to the concurrent spectrographic experiments, Vulcan planet search, and Einstein verification studies, as time progressed. Issues of funding and staff allotment for the expeditions, research, and timely publication of images and scientific results will be discussed. The effectiveness of the Observatory relying on volunteers to conduct a good deal of the eclipse work will be examined. There will be a discussion of optical design for the production of large sized eclipse images. The study will focus on the advantages and disadvantages of fixed cameras versus clock-driven movable instruments and refractor versus reflector optical configurations. Optical specifications of aperture and focal length suitable for coronal image making with the photographic emulsions and reproduction methods of the time will be looked at. Within this study, the Schaeberle Camera will receive its classification amongst other eclipse cameras with its performance characteristics being evaluated and compared. A study will be made to show the level of cooperation present between the Observatory and other national and international institutions. Any major involvement with astronomical organizations and their eclipse committees will be summarized. The educational benefits to the general public and the public relations role of the eclipse expeditions will be noted. The founding of the Astronomical Society of the Pacific will be discussed because of its intertwinement with the preparations for the first Lick Observatory eclipse expedition in January 1889. The Observatory faced continuous budget deficiencies and the impact on the publication of eclipse results will be surveyed in this light. The thesis will conclude with a series of remarks to summarize the findings of the thesis. The advancement in camera design in regards to the Schaeberle Camera and photographic processes for solar eclipse image making will be summarized. A reflection on the modernization of the Lick eclipse expeditions will be given. Advancements in analytical techniques for data reduction will be noted. The key contributions of the Observatory to our knowledge of the solar corona will be summarized. Results of other institutions made latter in the nineteenth century by their use of the plates of the Schaeberle Camera will be briefly noted. The Lick Observatory solar eclipse expeditions and solar eclipse research program will be given its place in the grand scheme of the study of solar physics.

Intensity Oscillation in the Corona as Observed during the Total Solar Eclipse of 29 March 2006

Abstract: We obtained the images of the eastern part of the solar corona in the Fe xiv 530.3 nm (green) and Fe x 637.4 nm (red) coronal emission lines during the total solar eclipse of 29 March 2006 at Manavgat, Antalya, Turkey. The images were obtained using a 35 cm Meade telescope equipped with a Peltier-cooled 2k × 2k CCD and 0.3 nm pass-band interference filters at the rates of 2.95 s (exposure times of 100 ms) and 2.0 s (exposure times of 300 ms) in the Fe xiv and Fe x emission lines, respectively. The analysis of the data indicates intensity variations at some locations with period of strongest power around 27 s for the green line and 20 s for the red line. These results confirm earlier findings of variations in the continuum intensity with periods in the range of 5 to 56 s by Singh et al. (Solar Phys.170, 235, 1997). The wavelet analysis has been used to identify significant intensity oscillations at all pixels within our field of view. Significant oscillations with high probability estimates were detected for some locations only. These locations seem to follow the boundary of an active region and in the neighborhood, rather than within the loops themselves. These intensity oscillations may be caused by fast magneto-sonic waves in the solar corona and partly account for heating of the plasma in the corona.

Solar corona during the total solar eclipse on August 1, 2008

Abstract: Shape and structure of the solar corona during the August 1, 2008, total solar eclipse is reported. The August 1, 2008, corona is classified as of near-minimum type with well developed northern and southern polar ray systems over polar coronal holes and several streamers of different brightness at the middle and low heliographic latitude. The flattening index was found to be 0.21.

Baily’s Beads Atlas in 2005 – 2008 Eclipses

Abstract: In the annular or total eclipses of 3 October 2005, 29 March 2006, 22 September 2006, and 1 August 2008, observational campaigns were organized to record the phenomenon of Baily’s beads. These campaigns were internationally coordinated through the International Occultation Timing Association (IOTA) at both its American and European sections. From the stations in the northern and southern zones of grazing eclipse, the eclipses have been recorded on video. Afterward, as many beads as possible have been identified by analyzing the video data of each observing station. The atlas presented in this paper includes 598 data points, obtained by 23 observers operating at 28 different observing stations. The atlas lists the geographic positions of the observing stations and the observed time instants of disappearance or reappearance of beads, identified by an angle measured relative to the Moon’s axis of rotation. The atlas will serve as a basis for determining the solar diameter.

The polarization of the solar corona on March 29, 2006

Abstract: The effect of the auroral ring on the polarization of the solar corona during the solar eclipse of March 29, 2006 is studied. The angle and degree of polarization for emission arising from the combination of two partially polarized components is calculated. The emission of each component is described in terms of the Stokes parameters, and the corresponding parameters added. The position angle and degree of polarization are found for all cases realized in observations of the polarized corona with polarizing filter positions of 0°, 60°, 120° and 0°, 45°, and 90°. These calculations indicate that singular polarization points (saddles with index −1/2) arise at a distance of about 1R⊙ from the limb. A model for the total emission of the corona is constructed, which is used to calculate deviations of the polarization plane from the tangential direction (with respect to the limb).

The search for vulcanoids in the 2008 total solar eclipse

Abstract: Interior to Mercury’s orbit is a dynamically stable region where a population of small, asteroid-like bodies called Vulcanoids has been hypothesized to reside The Vulcanoid Zone (VZ) extends inward from about 018 au to about 008 au During the Total Solar Eclipse (TSE) in 2008, a search for Vulcanoids was completed Although no Vulcanoids was detected to a moving object detection limit of V=128, the search was far more comprehensive than previous searches

Near infrared spectral and polarization imaging observation of coronal emission lines during the 2008 total solar eclipse

Abstract: During the 2008 total solar eclipse, the coronal emission lines were observed by using optical fibre spectrometric and polarization imaging system in near infrared waveband. The profiles of the coronal emission lines including Fe XIII 10747 A, 10798 A and He I 10830 A were obtained with dispersion of 0.5 A /pix. The intensity of Fe XIII 10747 A remained unchanged in the two different coronal regions while the intensity of He I 10830 A varied considerably in the two coronal locations no matter whether the prominence appeared or not. The coronal polarization images were observed at Fe XI 7892 A with a bandpass of 30 A in a series of exposure times.

3D Coronal Structures and Magnetic Field During the Total Solar Eclipse of 29 March 2006

Abstract: The good quality of the observing sequence of about 60 photographs of the white-light corona taken during the total solar eclipse observations on 29 March 2006, in Al Sallum, Egypt, enable us to use a new method of image processing for enhancement of the fine structure of coronal phenomena. We present selected magnetic-field lines derived for different parameters of the extrapolation model. The coincidence of the observed coronal white-light fine structures and the computed field-line positions provides a 3D causal relationship between coronal structures and the coronal magnetic field.

Observations of temperature and air humidity during the total solar eclipse 29 March 2006 at Side, Turkey

Abstract: Air temperature and relative humidity were measured during the total solar eclipse 29 March 2006 at Side, Turkey (N36°45.95'; E31°23.71') at screen height. The temperature was reduced by 5.0°C from the start of the eclipse until totality and increased by 4.3°C after totality. An overestimation of the temperature drop during the eclipse due to a radiation effect on the temperature measurement of ∼0.5°C cannot be excluded. The relative humidity followed an inverse pattern compared to air temperature during the eclipse. In contrast, the vapour pressure varied little during the eclipse and did not appear to be systematically affected by the eclipse conditions.

Broadband radio spectral observations of the solar eclipse on 2008-08-01 and its implications on the quiet Sun atmospheric model

Abstract: Based on the joint-observations of the radio broadband spectral emissions of the solar eclipse on August 1, 2008 at Jiuquan (total eclipse) and Huairou (partial eclipse) at the frequencies of 2.00–5.60 GHz (Jiuquan), 2.60–3.80 GHZ (Chinese solar broadband radiospectrometer, SBRS/Huairou), and 5.20–7.60 GHz (SBRS/Huairou), the authors assemble a successive series of broadband spectra with a frequency of 2.60–7.60 GHz to observe the solar eclipse synchronously. This is the first attempt to analyze the solar eclipse radio emission under the two telescopes located at different places with broadband frequencies in the periods of total and partial eclipses. With these analyses, the authorsmade a semiempirical model of the coronal plasma density of the quiet Sun, which can be expressed as ne ≃ 1.42×109(r−2+1.93r−5) (cm−3), in the space range of r=1.039–1.212 R⊙, and made a comparison with the classic model.

A potential lag between the open solar magnetic source flux and solar EUV and X-ray emissions as measured by the Earth's ionosphere during total solar eclipses

Abstract: Measurements of the ionospheric E-region during total solar eclipses have been used to provide information about the evolution of the solar magnetic field and EUV and X-ray emissions from the solar corona and chromosphere. By measuring levels of ionisation during an eclipse and comparing these measurements with an estimate of the unperturbed ionisation levels (such as those made during a control day, where available) it is possible to estimate the percentage of ionising radiation being emitted by the solar corona and chromosphere. Previously unpublished data from the two eclipses presented here are particularly valuable as they provide information that supplements the data published to date. The eclipse of 23 October 1976 over Australia provides information in a data gap that would otherwise have spanned the years 1966 to 1991. The eclipse of 4 December 2002 over Southern Africa is important as it extends the published sequence of measurements. Comparing measurements from eclipses between 1932 and 2002 with the solar magnetic source flux reveals that changes in the solar EUV and X-ray flux lag the open source flux measurements by approximately 1.5 years. We suggest that this unexpected result comes about from changes to the relative size of the limb corona between eclipses, with the lag representing the time taken to populate the coronal field with plasma hot enough to emit the EUV and X-rays ionising our atmosphere.

The calibration and initial results of the HeI D3 line flash spectrum obtained during the 2008 total solar eclipse

Abstract: The flash spectra in the HeI D3 line were obtained during the 2008 total solar eclipse. This paper describes the instrument and the calibration of the obtained flash spectrum, and presents our initial results. The average integrated intensity is E ave = 8.13 × 1013 erg·cm−1·s−1·ster−1 at h = 1100 km, which confirms that the HeI D3 emission is negatively correlated with the solar activity. The surface brightness reaches a maximum of F ave = 8.25×105 erg·cm−2·s−1·ster−1 at about h ≈ (1290 ± 75) km and then decreases exponentially with height when h > 1800 km with an exponential index β = 1.63×10−8 cm−1.

Records of solar eclipse observations in ancient China

Abstract: Like ancient people at other places of the world, the ancient Chinese lived in awe of the Sun. As they felt solar eclipses extremely significant events, they closely observed the occurrence of solar eclipse. Ancient astronomers further realized very early that solar eclipses were one of the important astronomical phenomena to revise and improve the ancient calendar. Interestingly, ancient emperors regarded solar eclipses as warnings from heaven that might affect the stability of their throne. Consequently, observing and recording solar eclipses became official, which dated far back to ancient China when numerous relevant descriptions were recorded in historical books. These records contribute substantially to China as an ancient civilization, as well as to the research of the long-term variation of the rotation rate of the Earth during >2000 years before the 17th century. This paper briefly reviews the perception, observations and recording of solar eclipses by ancient Chinese astronomers.

Coronal structure and brightness profile of the total solar eclipse on August 1, 2008

Abstract: Solar corona is the outermost part of the solar atmosphere. Coronal activities influence space environment between the Sun and the Earth, space weather and the Earth itself. The total solar eclipse (TSE) is the best opportunity to observe the solar corona on ground. During the TSE 2008, a series of images of the corona and partial eclipse of solar disk were obtained using telescope and CCD camera. After image processing, preliminary results of coronal structure are given, and radial brightness profiles of the corona in directions of pole and equator of the Sun are measured. Though in solar activity minimum, the shape and structure of the corona are not symmetry. The equatorial regions are more extent than the polar one, and there are also larger differences between the east and west equatorial regions and between the south and north polar regions. Coronal streamers on east side of the equator, particularly the largest one in east-south direction, are very obvious. The coronal plume in south polar region consists of more polar rays than that in north polar region. These structures are also shown in other observations and data of SOHO. The radial brightness profiles in directions of pole and equator are similar to those of the Van de Hulst model in solar minimum, but there are a few differences due to coronal activity, which is shown in the isophote map of the corona.