1,721,030 research outputs found
Visual and photoelectric measurements of the solar diameter (1972-2002): Methods and results
No full textMeasurements of the solar diameter using both visual and photoelectric drift scan techniques have been made since 1972 using two almost identical 45-cm Gregory-Coude telescopes at Locarno/Switzerland and Iza (n) over tildea/Tenerife. The method, in which a time measurement substitutes an angular measurement, is especially suited to obtain about 30 measurements of the absolute solar semidiameter per day. During the years 1972-2002 a total of 10996 visual timing measurements have been made on 320 observing days, an additional 1373 photoelectric recordings have been obtained on 117 observing days. The data were used to study the long-term behaviour of the solar semidiameter R at unit distance and its possible variations. No fluctuations dR in excess of about +/-0.05" have been found, neither long-term nor short-term. The photoelectric semidiameter, which refers to the continuum at lambda approximate to 585 nm, is Rphot = (959.89 +/- 0.12)". The visual semidiameter, which refers to the footpoint of the limb intensity profile at lambda approximate to 550 nm, is Rvis = (960.62 +/- 0.02)"
Ein Pionier und Wegbereiter der Astrophysik
No full textKarl Schwarzschild (1873–1916) gilt weltweit als einer der begabtesten und bedeutendsten Astronomen aller Zeiten und als Mitbegründer der Astrophysik. Geboren in Frankfurt am Main, wirkte er von 1901 bis 1909 als Professor für Astronomie und Direktor der Sternwarte in Göttingen und von 1909 bis 1916 als Direktor des Astrophysikalischen Observatoriums in Potsdam. Im Laufe seines allzu kurzen Lebens veröffentlichte Schwarzschild etwa 150 wissenschaftliche Arbeiten, viele davon von fundamentaler Bedeutung für die Entwicklung der Astronomie und Astrophysik. Aus Anlass seines 100. Todestages fand am 19. Mai 2016 in einer seiner früheren Wirkungsstätten, der heutigen Historischen Sternwarte in Göttingen, ein Gedenk-Kolloquium statt. Die schriftlichen Fassungen der dabei gehaltenen Vorträge sind, ergänzt um einen am 8. September 2016 anlässlich der Eröffnung der Schwarzschild-Ausstellung in der Fakultät für Physik gehaltenen Vortrag, im vorliegenden Band abgedruckt
Proceedings of a Workshop held at Göttingen September 27-29, 2006
No full textAn international workshop entitled: Modern Solar Facilities – Advanced Solar Science was held in Göttingen from September 27 until September 29, 2006. The workshop, which was attended by 88 participants from 24 different countries, gave a broad overview of the current state of solar research, with emphasis on modern telescopes and techniques, advanced observational methods and results, and on modern theoretical methods of modelling, computation, and data reduction in solar physics. This book collects written versions of contributions that were presented at the workshop as invited or contributed talks, and as poster contributions
A rare anatomical variation newly identifies the brains of C.F. Gauss and C.H. Fuchs in a collection at the University of Göttingen.
No full textCenter-to-limb variation of solar granulation from partial eclipse observations
No full textWe have measured the center-to-limb variation (CLV) of parameters describing geometric and photometric statistical properties of the solar granulation at 6708 A. This work is based on an excellent series of white-light images obtained with the Swedish Vacuum Solar Telescope at Rogue de los Muchachos Observatory, La Palma, during the partial solar eclipse of 1994 May 10. The lunar limb profile, which is visible in each frame, was used as a calibration tool for estimating the point-spread function of the combined optical system formed by the atmosphere and the telescope. Before restoration, noise was removed from the images by a novel application of the so-called optimum filter for two-dimensional objects. The latter was optimized in terms of rms error and was constructed from very precise smoothed models of the specific power spectrum of the granulation at each position on the solar disk. The determination of the positions on the solar disk was achieved with high accuracy by matching the position of the Moon's limb in our images to a numerical simulation of the eclipse geometry. The CLV curve of the Delta I(rms) granular contrast shows one of the steepest gradients among those reported in the literature and quite a high value (9.6%) at the disk center considering that our working wavelength is in the far-red range of the solar spectrum. The elliptical shape of the restored power spectra with ellipticities equal to those expected just from foreshortening proves that radiative transfer effects do not alter the isotropy of the horizontal intensity pattern of the solar granulation, at least up to mu = 0.4. The mean wavenumber, (k) over bar, derived from the two-dimensional power spectra azimuthally integrated along the ellipses amounts to a value of 6.15 Mm(-1) at the center of the solar disk and then shows a decrease toward the limb. Apart from the power spectra analysis, a direct statistical study of the granulation size and brightness, based on the image segmentation for defining granular contours, has also been performed. A general increase in both granular and intergranular areas is found as we move toward the solar limb. The mean granular cell area varies from 1.36 Mm(2) at mu = 1 up to 2.06 Mm(2) at mu = 0.6, and in parallel, the granular filling factor (the percentage of area of the image covered by granules) decreases from 44.2% to 42.8%. In the small area range, the granular brightness increases linearly with the granular cell size and is preserved constant, on average, for granular cells larger than similar to 2." 0. No slope variation is found for the intergranular intensities versus granular cell areas. Observations close to the solar limb detect granular structures as small as 0." 53 or even smaller up to a distance of at least approximate to 0." 5 from the limb, showing that the AT associated with the granulation persist at least until z approximate to 200 km. However, this penetration could be different for small and large granules because we find several hints indicating the progressive disappearance of small structures toward the limb
Center-to-limb variation of solar granulation from partial eclipse observations
No full textWe have measured the center-to-limb variation (CLV) of parameters describing geometric and photometric statistical properties of the solar granulation at 6708 A. This work is based on an excellent series of white-light images obtained with the Swedish Vacuum Solar Telescope at Rogue de los Muchachos Observatory, La Palma, during the partial solar eclipse of 1994 May 10. The lunar limb profile, which is visible in each frame, was used as a calibration tool for estimating the point-spread function of the combined optical system formed by the atmosphere and the telescope. Before restoration, noise was removed from the images by a novel application of the so-called optimum filter for two-dimensional objects. The latter was optimized in terms of rms error and was constructed from very precise smoothed models of the specific power spectrum of the granulation at each position on the solar disk. The determination of the positions on the solar disk was achieved with high accuracy by matching the position of the Moon's limb in our images to a numerical simulation of the eclipse geometry. The CLV curve of the Delta I(rms) granular contrast shows one of the steepest gradients among those reported in the literature and quite a high value (9.6%) at the disk center considering that our working wavelength is in the far-red range of the solar spectrum. The elliptical shape of the restored power spectra with ellipticities equal to those expected just from foreshortening proves that radiative transfer effects do not alter the isotropy of the horizontal intensity pattern of the solar granulation, at least up to mu = 0.4. The mean wavenumber, (k) over bar, derived from the two-dimensional power spectra azimuthally integrated along the ellipses amounts to a value of 6.15 Mm(-1) at the center of the solar disk and then shows a decrease toward the limb. Apart from the power spectra analysis, a direct statistical study of the granulation size and brightness, based on the image segmentation for defining granular contours, has also been performed. A general increase in both granular and intergranular areas is found as we move toward the solar limb. The mean granular cell area varies from 1.36 Mm(2) at mu = 1 up to 2.06 Mm(2) at mu = 0.6, and in parallel, the granular filling factor (the percentage of area of the image covered by granules) decreases from 44.2% to 42.8%. In the small area range, the granular brightness increases linearly with the granular cell size and is preserved constant, on average, for granular cells larger than similar to 2." 0. No slope variation is found for the intergranular intensities versus granular cell areas. Observations close to the solar limb detect granular structures as small as 0." 53 or even smaller up to a distance of at least approximate to 0." 5 from the limb, showing that the AT associated with the granulation persist at least until z approximate to 200 km. However, this penetration could be different for small and large granules because we find several hints indicating the progressive disappearance of small structures toward the limb
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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