Aims. Digital images of observations printed in the books Rosa Ursina sive solis and Prodromus pro sole mobili by Christoph Scheiner, as well as the drawings from Scheiner’s letters to Marcus Welser, ...are analysed to obtain information on the positions and sizes of sunspots that appeared before the Maunder minimum. Methods. In most cases, the given orientation of the ecliptic is used to set up the heliographic coordinate system for the drawings. Positions and sizes are measured manually on screen. Very early drawings have no indication of their orientation. A rotational matching using common spots of adjacent days is used in some cases, while in other cases, the assumption that images were aligned with a zenith-horizon coordinate system appeared to be the most probable. Results. In total, 8167 sunspots were measured. A distribution of sunspot latitudes versus time (butterfly diagram) is obtained for Scheiner’s observations. The observations of 1611 are very inaccurate, the drawings of 1612 have at least an indication of their orientation, while the remaining part of the spot positions from 1618−1631 have good to very good accuracy. We also computed 697 tilt angles of apparently bipolar sunspot groups observed in the period 1618−1631. We find that the average tilt angle of nearly 4 degrees is not significantly different from 20th-century values.
The number of spots on the surface of the Sun is one of the best tracers of solar variability we have. The sunspot number is not only known to change in phase with the 11-year solar cycles, but also ...to show variability on longer time scales. It is, however, not only the sunspot number that changes in connection with solar variability. The location of the spots on the solar surface is also known to change in phase with the 11-year solar cycle. This has traditionally been visualised in the so-called butterfly diagram, but this is only well constrained from the beginning of the 19th century. This is unfortunate, as knowledge about the butterfly diagram could aid our understanding of the variability and the Sun–Earth connection.
As part of a larger review of the work done on sunspots by the Danish astronomer Christian Horrebow, we here present a reanalysis of Christian Horrebow’s notebooks covering the years 1761 and 1764 – 1777. These notebooks have been analysed in at least three earlier studies by Thiele (
Astron. Nachr.
50
, 257,
1859
), d’Arrest (published in Wolf,
Astron. Mitt. Eidgenöss. Sternwarte Zür
.
4
, 77,
1873
) and Hoyt and Schatten (
Solar Phys.
160
, 387,
1995
). In this article, we construct a complete record of sunspot positions covering the years 1761 and 1764 – 1777. The resulting butterfly diagram shows the characteristic structure known from observations in the 19th and 20th century. We do see some indications of equatorial sunspots in the observations we have from Cycle 1. However, in Cycle 2, which has much better coverage, we do not see such indications.
Between 1761 and 1776, Christian Horrebow made regular observations of sunspots from Rundetårn in Copenhagen. Based on these observations he writes in 1775 that “it appears that after the course of a ...certain number of years, the appearance of the Sun repeats itself with respect to the number and size of the spots”. Thus, Horrebow hypothesized the idea of a cyclic Sun several decades before Heinrich Schwabe discovered the solar cycle and estimated its period. This proves the ability of Horrebow as a sunspot observer. In this article, we present a general overview of the work of Christian Horrebow, including a brief biography and a complete bibliography. We also present a translation from Danish to English of his writings on sunspots in the
Dansk Historisk Almanak
. These writings include tables of daily sunspot measurements of which we discuss the completeness.
An analysis of the sunspot observations made by Hevelius during 1642-1645 is presented. These records are the only systematic sunspot observations just before the Maunder Minimum (MM). We have ...studied different phenomena meticulously recorded by Hevelius after translating the original Latin texts. We reevaluate the observations of sunspot groups by Hevelius during this period and obtain an average value 7% greater than that calculated from his observations given in the current group database. Furthermore, the average of the active day fraction obtained in this work from Hevelius's records previous to the MM is significantly greater than the solar activity level obtained from Hevelius's sunspot observations made during the MM (70% versus 30%). We also present the butterfly diagram obtained from the sunspot positions recorded by Hevelius for the period 1642-1645. It can be seen that no hemispheric asymmetry exists during this interval, in contrast with the MM. Hevelius noted a ∼3-month period that appeared to lack sunspots in early 1645 that gave the first hint of the impending MM. Recent studies claim that the MM was not a grand minimum period, speculating that astronomers of that time, due to the Aristotelian ideas, did not record all sunspots that they observed, producing thus an underestimation of the solar activity level. However, we show that the good quality of the sunspot records made by Hevelius indicates that his reports of sunspots were true to the observations.
Aims. Extending the knowledge about the properties of solar cycles into the past is essential for understanding the solar dynamo. This paper aims to estimate areas of sunspots observed by Schwabe in ...1825−1867 and to calculate the tilt angles of sunspot groups. Methods. The sunspot sizes in Schwabe’s drawings are not to scale and need to be converted into physical sunspot areas. We employed a statistical approach assuming that the area distribution of sunspots was the same in the 19th century as it was in the 20th century. Results. Umbral areas for about 130 000 sunspots observed by Schwabe were obtained, as well as the tilt angles of sunspot groups assuming them to be bipolar. There is, of course, no polarity information in the observations. The annually averaged sunspot areas correlate reasonably with sunspot number. We derived an average tilt angle by attempting to exclude unipolar groups with a minimum separation of the two alleged polarities and an outlier rejection method which follows the evolution of each group and detects the moment it turns unipolar at its decay. As a result, the tilt angles, although displaying considerable scatter, average to 5̊.85 ± 0, with the leading polarity located closer to the equator, in good agreement with tilt angles obtained from 20th century data sets. Sources of uncertainties in the tilt angle determination are discussed and need to be addressed whenever different data sets are combined. The sunspot area and tilt angle data are provided at the CDS.
The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, has been continously available since 1874 using data from the Royal Greenwich Observatory, extended by SOON ...network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence since 1826, using the recently digitized data from Schwabe (1826–1867) and Spörer (1866–1880). The wings of the diagram are separated using a recently developed method based on an analysis of long gaps in sunspot group occurrence in different latitude bands. We define characteristic latitudes, corresponding to the start, end, and the largest extent of the wings (the F, L, and H latitudes). The H latitudes (30°–45°) are highly significantly correlated with the strength of the wings (quantified by the total sum of the monthly numbers of sunspot groups). The F latitudes (20°–30°) depict a weak tendency, especially in the southern hemisphere, to follow the wing strength. The L latitudes (2°–10°) show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have a greater wing extent. A strong (5–6)-cycle periodic oscillation is found in the start and end times of the wings and in the overlap and gaps between successive wings of one hemisphere. While the average wing overlap is zero in the southern hemisphere, it is two to three months in the north. A marginally significant oscillation of about ten solar cycles is found in the asymmetry of the L latitudes. The new long database of butterfly wings provides new observational constraints to solar dynamo models that discuss the spatio-temporal distribution of sunspot occurrence over the solar cycle and longer.
Sunspot positions from various historical sets of solar drawings are analyzed with respect to the tilt angles of bipolar sunspot groups. Data by Scheiner, Hevelius, Staudacher, Zucconi, Schwabe, and ...Spörer deliver a series of average tilt angles spanning a period of 270years, additional to previously found values for 20th-century data obtained by other authors. We find that the average tilt angles before the Maunder minimum were not significantly different from the modern values. However, the average tilt angles of a period 50years after the Maunder minimum, namely for cycles 0 and 1, were much lower and near zero. The normal tilt angles before the Maunder minimum suggest that it was not abnormally low tilt angles which drove the solar cycle into a grand minimum.
The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote sensing instrument on Solar Orbiter that observes the hard X-ray bremsstrahlung emission of solar flares. This paper describes the ...STIX Aspect System (SAS), a subunit that measures the pointing of STIX relative to the Sun with a precision of
±
4
″
, which is required to accurately localize the reconstructed X-ray images on the Sun. The operating principle of the SAS is based on an optical lens that images the Sun onto a plate that is perforated by small apertures arranged in a cross-shaped configuration of four radial arms. The light passing through the apertures of each arm is detected by a photodiode. Variations of spacecraft pointing and of distance from the Sun cause the solar image to move over different apertures, leading to a modulation of the measured lightcurves. These signals are used by ground analysis to calculate the locations of the solar limb, and hence the pointing of the telescope.
Solar physics at the Einstein Tower Denker, C.; Heibel, C.; Rendtel, J. ...
Astronomische Nachrichten,
11/2016, Letnik:
337, Številka:
10
Journal Article
We report the characterization of ZnO homojunction fabricated with undoped (
n-ZnO) and AlN codoped ZnO (
p-ZnO) films by RF magnetron sputtering. We directly doped (codoped) AlN into ZnO to obtain
...p-ZnO instead of conventional codoping method. The Current-Voltage characteristics of the fabricated
p-n junction show a typical rectification behavior. The junction parameters such as ideality factor (11.85), barrier height (0.782 eV) and series resistance (33 kΩ) have been determined using Cheung’s method. The barrier height (0.805 eV) determined by Norde’s method is also in good agreement with Cheung’s method.
► In this paper, we discussed about the characterization of
p-
n junction fabricated with undoped ZnO (
n-type) and AlN codoped ZnO (
p-type) ► The fabricated junction on Si (100) by RF magnetron sputtering has been subjected to XRD, AFM, EDS, PL, Hall measurements and I-V characterization ► It has been demonstrated that the fabricated ZnO homojunction is suitable for optoelectronic and gas sensor devices
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