Short-period intensity oscillations in the solar corona observed during the total solar eclipse of 26 February 1998

Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01–0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5–3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse.     

Limits on radiative decays of solar neutrinos from measurements during a total solar eclipse

During the 1999 total solar eclipse we intended to search for photons emitted by a possible radiative decay of the heavier component of solar neutrinos, using two telescopes: an airborne one, and another at mountain altitude, in Romania(the NOTTE experiment). The weather conditions did not allow us to perform the measurements. Alternatively, we analyzed a video tape of the eclipse offered to us by a local television, obtaining some qualitative estimations on the neutrino lifetimes. We present also a first report on the observations made 21 June 2001, from Zambia. This revised version was published online in July 2006 with corrections to the Cover Date.     

Changes in the concentration of mesospheric ozone during the total solar eclipse

Measurements of dayglow radiance of $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{g}}\text{)}$ and OH(7,2) bands are reported. Ground based photometers were used to monitor zenith radiance of 1270 and 694 nm emissions during the total solar eclipse of 16 February 1980. Altitude distribution of 1270 nm intensity was derived from ground based observations. A set of altitude distributions of $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{g}}\text{)}$ were thus obtained throughout the eclipse. These altitude distributions were converted into ozone distributions using the rate equations for formation and loss of ozone and $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{g}}\text{)}$ molecules. Results indicate an increase in the ozone concentration at mid-eclipse. OH(7,2) emission did not show enhancement during totality. This may mean that there was no increase in OH concentration during the eclipse.     

Observations of the solar corona in polarized white light during the total solar eclipse of February 16, 1980: Preliminary results

Photographic observations of the corona were made by a Belgian expedition to Kenya during the eclipse of 1980, February 16, using a polaroïd filter oriented in three directions 60 ° apart. The preliminary results of the reduced data are presented here; these results consist in the analysis of the three following parameters: total intensity, degree of polarization, direction of the electric vector. The local variation of these parameters reveals, among other features, a deep coronal hole at the south pole and peculiar streamer (P.A. 280 °) associated to a transient, (the so-called tennis racket) also observed by other teams, and a density enhancement at P.A. 200 °, possibly associated with a transient observed with the K-coronameter of the High Altitude Observatory 12 hr before the eclipse.     

Structure and shape of the solar corona during the total solar eclipse on March 29, 2006

The structure and the shape of the solar corona during the total solar eclipse on March 29, 2006 were studied. The corona was of the intermediate pre-minimal type, it had northern and southern polar ray systems above the polar coronal holes and six streamers of different brightness in the middle and low heliographic latitudes. All the coronal structural features were found to have counterparts at the photosphere-chromosphere level on the limb and near it. The corona’s photometric flattening index was equal to 0.17.     

Spectropolarimetric analysis of the solar corona during the 12 November 1966 total eclipse

Spectropolarimetric observations of the solar corona during the 12 November, 1966 total eclipse are analyzed. The trend of the intensity, the polarization degree p, and the polarization angle α of the coronal continuum are given as functions of ρ and compared with those of other authors. The H and K Caii lines have been observed in emission once again and, through a quantitative analysis, are attributed to scattered prominence light instead of to the corona as previously made.     

Sunspot and stray light observations during the 1971, February 25 partial solar eclipse

Observations of a sunspot during and after a partial solar eclipse are described. The amount of scattered light confirms the existence of a spread function component with a half width of 10″. The observations also indicate the possibility of severely underestimating this component by aureole measurements. Umbral continuum intensities of 0.10 I _⊙ in the red spectral region were directly measured, the correction for scattered light amounts to 0.02 I _⊙. Intensities calculated with four umbral models are larger than the observed values, indicating this sunspot to be cooler by some 100 K. The wings of two strong Ca i lines are equally explained by the models of Henoux, Kneer, and Stellmacher/Wiehr. Yun's model can be ruled out because of too high a temperature.     

Constraints on the origin and evolution of the layered mound in Gale Crater, Mars using Mars Reconnaissance Orbiter data

Gale Crater contains a 5.2 km-high central mound of layered material that is largely sedimentary in origin and has been considered as a potential landing site for both the MER (Mars Exploration Rover) and MSL (Mars Science Laboratory) missions. We have analyzed recent data from Mars Reconnaissance Orbiter to help unravel the complex geologic history evidenced by these layered deposits and other landforms in the crater. Results from imaging data from the High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) confirm geomorphic evidence for fluvial activity and may indicate an early lacustrine phase. Analysis of spectral data from the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) instrument shows clay-bearing units interstratified with sulfate-bearing strata in the lower member of the layered mound, again indicative of aqueous activity. The formation age of the layered mound, derived from crater counts and superposition relationships, is ∼3.6-3.8 Ga and straddles the Noachian-Hesperian time-stratigraphic boundary. Thus Gale provides a unique opportunity to investigate global environmental change on Mars during a period of transition from an environment that favored phyllosilicate deposition to a later one that was dominated by sulfate formation.     

Identification of a solar X-ray source using D layer ionization behavior during an eclipse

Semi-quantitative reports of shortwave radio reception during the 12 November 1966 total solar eclipse have been used to determine the characteristics of a major source of D layer ionization. An effective electron depletion coefficient of 1.2 × 10^–2 sec^–1 was found empirically and used to reduce the data. Analysis of the radio absorption shows the source was located near heliographic coordinates, B = +7°, L = 340° and was probably less than 0.5 of arc in diameter. At the time of the eclipse, the source accounted for 40% of the radio absorption on a single, vertical pass through the D layer. Preoccultation behavior of the signal strength is interpreted by assuming a portion of the source X-ray flux was reflected at grazing incidence from the limb of moon. For point sources, such reflections have specific chromatic characteristics which were used to derive a crude source spectrum in the 3–140 Å range. X-ray absorption edges of N, O, Na, Be, and possible Mg, Ar, Ne, Ca, and K arising from the terrestrial atmosphere have been identified. A source temperature approximately twice that of the rest of the corona is indicated.     

The spectrum of the inner corona observed during the total solar eclipse of 30 May 1965

A series of spectrograms of the inner solar corona were obtained at the total solar eclipse of 30 May 1965 using a fast spectrograph with a circular slit that recorded the spectrum from 3000 to 9000 at all position angles around the limb simultaneously. In this paper absolute intensity is given as a function of position angle for the stronger lines and the continuum. In the coronal enhancement or condensation centered at heliocentric position angle 293°, absolute intensity is given for 34 forbidden emission lines and the continuum.     

Changes in solar irradiance and atmospheric turbidity in Costa Rica during the total solar eclipse of July 11, 1991

Solar global radiation was measured in several places in Costa Rica during the total solar eclipse that occurred on July 11, 1991. In two of these places, Puntarenas and Santa Cruz, measurements in the ultraviolet range (295–385 nm) were also taken. In Santa Cruz, a normal incidence pyrheliometer with Schott filters OG530 and RG630 was used to measure direct solar radiation in its whole range, and in the 530–2800 nm and 630–2800 wavebands respectively. Global radiation, and consequently direct, diffuse and irradiance in any of the wavebands considered, decreased gradually as the sun was being eclipsed and reached zero during the totality, then increased to their normal values. Data registered in Santa Cruz were used to determine Ångstrom's atmospheric turbidity parameters and. Computations show that between 13:00 and 14:30 LT (local time), decreased and increased significantly. This indicates that atmospheric turbidity was high and large particles were more abundant than small ones. The size of hygroscopic particles increased during the eclipse when temperature decreased and relative humidity increased in a comparatively short time.     

Timing of the 1984 total solar eclipse and the size of the sun

We report accurate timing of second and third contacts made from videotape of the total solar eclipse of 23 November, 1984, observed in Papua New Guinea. The magnitude of the discrepancies between predicted and observed times indicates that the secular change in the size of the Sun reported by some observers is within the uncertainty.     

The radial brightness distribution of the Sun at 3.2 mm as determined from the June 30, 1973 total solar eclipse and a reanalysis of the March 7, 1970 total solar eclipse

The radial brightness distribution of the Sun at 3.2 mm is recalculated for the 7 March, 1970 total solar eclipse by an improved method. The results from the first contact of the 30 June, 1973 total eclipse are also analyzed. Limb brightening is apparent for the 1970 eclipse when all four contacts are averaged. The 1973 eclipse indicates strong limb brightening, although the detailed shape differs from the 1970 eclipse.     

Photometric study of chromospheric and coronal spikes observed during the total solar eclipse of 30 June, 1973

A photometric and colorimetric analysis of a color picture of the very inner solar corona, near the South pole region, is performed. Dimensions and average electron densities of both chromospheric and very fine resolved coronal spikes are deduced. For the coronal spike a half width of 1.67 is measured, the estimate of electron density yields n _e = 10¹⁰ cm^–3. Some conclusions are attempted on the light of a simultaneously observed spectrum of the same region which appeared to be a disappearing coronal hole. The observations seem to support the concept of a striated corona.On leave from Institut d'Astrophysique, Paris as NRC Post-Doctoral Research Assistant.     

Observation and preliminary analysis of the chromospheric flash spectrum obtained during the total solar eclipse of 1980 February 16

A successful observation of the flash spectum was made using a slitless spectrograph in Rui-Li country, Yun-Nan province during the total solar eclipse of Feb. 16, 1980. The spectrograph fed by a coelostat has an average dispersion of 5.7 Å/mm. The spectrograms have a height resolution of 185 km.

A preliminary analysis of the observation has been made as follows. We have identified 1042 chromospheric lines ranging from 4799 Å to 5845 Å, 72 of which are not listed in /1/ or /2/. The location of the chromospheric base has been determined. The absolute photometric calibration was made by the spectra of the limb obtained by the slitless spectrograph before the second contact and the spectra of the disk center on the previous day. We have measured and calculated the Intensity of each spectral line near the base of the chromosphere. In addition to the chromospheric lines, we also obtained three coronal lines, 5300 Å (Fe XIV), 5445 Å and 5694 Å (Ca XV).     

Air temperature and wind changes in Costa Rica during the total solar eclipse of July 11, 1991

Air temperature and wind measurements on the surface and in the free atmosphere taken during the total solar eclipse of July 11, 1991, are analyzed. Surface air temperature decreased significantly, 2 to 5 °C in general, with the lowest values occurring 10 to 30 minutes after totality. In some places, surface wind speed decreased gradually during the eclipse, as a result of the decrease of air temperature and temperature gradients. In other places, it increased due to local atmospheric conditions. A radiosonde launched at 13:26 LT (local time) appeared to have been affected by the moon's shadow at about 13 km height. At this altitude temperature was relatively lower than usual and the balloon carrying the radiosonde experienced an upward acceleration. Also at this altitude wind direction changed and wind speed decreased     

Interferometric investigation of the red and green coronal lines during the total solar eclipse of May 30, 1965

Fabry-Pérot interferometric observations of the corona were carried out. The 6374 Å line shows radial velocities between 10 and 70 km sec^-1, both positive and negative. Most profiles of the 6374 Å line are not Gaussian. The widths of the lines indicate unacceptably high temperatures, and thus suggest turbulent velocities, which appear to be of the same order as the line displacement velocities. Arguments are put forward that the corona consists mainly of individual non-turbulent knots with relative velocities similar to the measured ones.     

Variation of the geomagnetic field in Costa Rica during the total solar eclipse of July 11, 1991

Ground measurements of the geomagnetic field, during the total solar eclipse of July 11, 1991, were carried out at three sites in Costa Rica located within the eclipse's path of totality. Near totality, there was a significant change in the total intensity,F. Its normal decrease in the afternoon hours was interrupted during a period of about 45 min, in whichF varied very little. This was due mainly to a small variation in horizontal intensity,H, during such a period. The departure ofF from normal lasted about 100 min; its maximum departure was near 10 nT and occurred about 38 min after totality, The declination,D, also experienced a small change (about 2.3 min) during the total period of the eclipse. The vertical intensity,Z, and the inclination,I, did not show significant changes.     

Determination of stray light and sunspot intensities based on the observation during the solar eclipse of 30 June, 1973

A program has been developed to evaluated the gravitational binding energy of a clumpy cluster composed ofN particles with a given mass dispersion, a given abundance of binaries and a given massive binary system at the centre. In application to clusters of galaxies nucleated by massivecD binaries, it is found that the gravitational binding energy is typically greater than the equivalent smooth distribution by a factor in the range 2–12. This suggests that the missing mass problem in clusters of galaxies can be reduced by an order of magnitude if the correct binding energy is used in the virial theorem.