Heliographic Positions Research Articles

Sunspot Observations at the Eimmart Observatory: Revision and Supplement

Digital images of sunspot drawings of the archives of Georg Christoph Eimmart stored at the National Library of Russia, St. Petersburg, are analyzed to obtain sunspot-group numbers and sunspot areas as well as heliographic positions. Overall, more than a hundred drawings were processed. The impact of drawing and reproduction uncertainties and the aims of historical observations are considered. The sunspot positions are compared to those reported by contemporary observers of the Maunder minimum. The restored sunspot-group numbers and latitudes are compared to those extracted by Hoyt and Schatten (Solar Phys. 179, 189, 1998) as well as Hayakawa et al. (Solar Phys. 296, 154, 2021b) and Hayakawa et al. (Astrophys. J. 909, 166, 2021d). The persistence of long-lived sunspots over several solar rotations is discussed.

Sunspot Positions and Areas from Observations by Cigoli, Galilei, Cologna, Scheiner, and Colonna in 1612 – 1614

Digital images of manuscripts stored in the Galilean collection of the Central National Library of Florence are analyzed to obtain sunspot groups, their areas and heliographic positions. Overall, 142 drawings were processed. The way of drawing is usually schematic resulting in area uncertainty which may exceed a factor of two for small sunspots. We suggest that there is an upper limit of a factor of two between sunspot group numbers from the drawings and the actual ones. The computed penumbra-to-umbra ratio is consistent with modern observations. A distribution of sunspot latitudes versus time is reconstructed by means of two methods: exploiting the observation time noted by an observer and minimizing the day-to-day variability of sunspot latitudes.

Solar differential rotation in the period 1964–2016 determined by the Kanzelhöhe data set

The main aim of this work is to determine the solar differential rotation by tracing sunspot groups during the period 1964-2016, using the Kanzelh\"ohe Observatory for Solar and Environmental Research (KSO) sunspot drawings and white light images. Two procedures for the determination of the heliographic positions were applied: an interactive procedure on the KSO sunspot drawings (1964 - 2008, solar cycles nos. 20 - 23) and an automatic procedure on the KSO white light images (2009 - 2016, solar cycle no. 24). For the determination of the synodic angular rotation velocities two different methods have been used: a daily shift (DS) method and a robust linear least-squares fit (rLSQ) method. Afterwards, the rotation velocities had to be converted from synodic to sidereal, which were then used in the least-squares fitting for the solar differential rotation law. For the test data from 2014, we found the rLSQ method for calculating rotational velocities to be more reliable than the DS method. The best fit solar differential rotation profile for the whole time period is $\omega(b)$ = (14.47 $\pm$ 0.01) - (2.66 $\pm$ 0.10) $\sin^2b$ (deg/day) for the DS method and $\omega(b)$ = (14.50 $\pm$ 0.01) - (2.87 $\pm$ 0.12) $\sin^2b$ (deg/day) for the rLSQ method. A barely noticeable north - south asymmetry is observed for the whole time period 1964 - 2016 in the present paper. Rotation profiles, using different data sets (e.g. Debrecen Photoheliographic Data, Greenwich Photoheliographic Results), presented by other authors for the same time periods and the same tracer types, are in good agreement with our results. Therefore, the KSO data set is suitable for the investigation of the long-term variabilities in the solar rotation profile.

Sunspots Areas and Heliographic Positions on the Drawings Made by Galileo Galilei in 1612

AbstractIn 1612, Galileo Galilei made very accurate drawings of the solar disk. Currently, 47 of them are in the open access: 9 in May 3 – 11, 35 in June and July, and 3 in late August. Unfortunately, reports have not provided the clock time, which results in uncertainty of sunspots heliographic coordinates. In the present study, we determine the exact time of the drawings by comparing the positions of the same spots from day to day. The time of the observations, which varies from 12 to 16 UT, gives us the direction of the solar rotation axis and the position of the helioequator. Unlike the spots drawn by Christopher Scheiner in 1611 – 1612, none of the analyzed spots lies within the helioequator. This confirms the quality of the Galileo’s drawings.

The Solar Rotation in the 1930s from the Sunspot and Flocculi Catalogs of the Ebro Observatory

The tables of sunspot and flocculi heliographic positions included in the catalogs published by the Ebro Observatory in the 1930s have recently been recovered and converted into digital format by using optical character recognition (OCR) technology. We here analyzed these data by computing the angular velocity of several sunspot and flocculi groups. A difference was found in the rotational velocity for sunspots and flocculi groups at high latitudes, and we also detected an asymmetry between the northern and southern hemispheres, which is especially marked for the flocculi groups. The results were then fitted with a differential-rotation law [ $\omega=a+b \sin^{2} B$ ] to compare the data obtained with the results published by other authors. A dependence on the latitude that is consistent with former studies was found. Finally, we studied the possible relationship between the sunspot/flocculi group areas and their corresponding angular velocity. There are strong indications that the rotational velocity of a sunspot/flocculi group is reduced (in relation to the differential rotation law) when its maximum area is larger.

The Solar Rotation in the Period 1853 – 1870 from the Sunspot Catalogues of Carrington, Peters, and de la Rue

R.C. Carrington, C.H.F. Peters, and W. de la Rue observed the sunspots in the second half of the nineteenth century, determining their heliographic positions between 1853 and 1870, before the solar program of the Royal Greenwich Observatory was established. The large tables of sunspot positions included in the catalogues published by these observers have recently been converted into a machine-readable format. The present work analyses these data by calculating the sunspot group velocities for each observer. The results are then fitted with a differential-rotation law to compare the data of the three observers with each other and with the results published by others. Finally, we study the possible relationship between the sunspot-group areas as determined by de la Rue and the corresponding sunspot-group velocities.

STEREO/Extreme Ultraviolet Imager (EUVI) Event Catalog 2006 – 2012

We generated an event catalog with an automated detection algorithm based on the entire EUVI image database observed with the two Solar Terrestrial Relations Observatory (STEREO)-A and -B spacecraft over the first six years of the mission (2006 – 2012). The event catalog includes the heliographic positions of some 20 000 EUV events, transformed from spacecraft coordinates to Earth-based coordinates, and information on associated GOES flare events (down to the level of GOES A5-class flares). The 304 Å wavelength turns out to be the most efficient channel for flare detection (79 % of all EUVI event detections), while the 171 Å (4 %), 195 Å (10 %), and the 284 Å channel (7 %) retrieve substantially fewer flare events, partially due to the suppressing effect of EUV dimming, and partially due to the lower cadence in the later years of the mission. Due to the Sun-circling orbits of STEREO-A and -B, a large number of flares have been detected on the farside of the Sun, invisible from Earth, or seen as partially occulted events. The statistical size distributions of EUV peak fluxes (with a power-law slope of α P =2.5±0.2) and event durations (with a power-law slope of α T =2.4±0.3) are found to be consistent with the fractal-diffusive self-organized criticality model. The EUVI event catalog is available on-line at secchi.lmsal.com/EUVI/euvi_autodetection/euvi_events.txt and may serve as a comprehensive tool to identify stereoscopically observed flare events for 3D reconstruction and to study occulted flare events.

Sunspot positions and sizes for 1825–1867 from the observations by Samuel Heinrich Schwabe

Samuel Heinrich Schwabe made 8486 drawings of the solar disk with sunspots in the period from November 5, 1825 to December 29, 1867. We have measured sunspot sizes and heliographic positions on digitized images of these drawings. A total of about 135,000 measurements of individual sunspots are available in a data base. Positions are accurate to about 5% of the solar radius or to about three degrees in heliographic coordinates in the solar disk center. Sizes were given in 12 classes as estimated visually with circular cursor shapes on the screen. Most of the drawings show a coordinate grid aligned with the celestial coordinate system. A subset of 1168 drawings have no indication of their orientation. We have used a Bayesian estimator to infer the orientations of the drawings as well as the average heliographic spot positions from a chain of drawings of several days, using the rotation profile of the present Sun. The data base also includes all information available from Schwabe on spotless days.

Solar energetic particle flux enhancement as a predictor of geomagnetic activity in a neural network‐based model

Coronal mass ejections (CMEs) are believed to be the principal cause of increased geomagnetic activity. They are regarded as being in context of a series of related solar energetic events, such as X‐ray flares (XRAs) accompanied by solar radio bursts (RSPs) and also by solar energetic particle (SEP) flux. Two types of the RSP events are known to be geoeffective, namely, the RSP of type II, interpreted as the signature of shock initiation in the solar corona, and type IV, representing material moving upward in the corona. The SEP events causing geomagnetic response are known to be produced by CME‐driven shocks. In this paper, we use the method of the artificial neural network in order to quantify the geomagnetic response of particular solar events. The data concerning XRAs and RSPs II and/or IV together with their heliographic positions are taken as the input for the neural network. There is a key question posed in our study: can the successfulness of the neural network prediction scheme based solely on the solar disc observations (XRA and RSP) be improved by additional information concerning the SEP flux? To resolve this problem, we chose the SEP events possessing significant enhancement in the 10‐h window, commencing 12 h after the generation of XRAs. In particular, we consider the flux of high‐energy protons with energies over 10 MeV. We have used a chi‐square test to demonstrate that supplying such extra input data improves the neural network prediction scheme.

Scattering polarization in strong chromospheric lines

Aims. We explore the spatial variations of the chromospheric Call K scattering polarization on the quiet Sun, in particular the fluctuations of the linear polarizations Q/I and U/f, their correlations, varying profile shapes, and center-to-limb variations. Methods. A set of high precision polarimetric recordings with ZIMPOL (Zurich Imaging Polarimeter) at distinct heliographic positions is used. Results. Two main effects contribute to the observed fluctuations: (i) Chromospheric magnetic fields (located in the K3 layer), which induce polarization variations via the Hanle effect. (ii) Hot spots due to small-scale temperature structuring of the chromosphere, which induce variations of the local scattering geometry. The observed signatures of both effects are influenced by the turbulent broadening, which steeply increases with height, by optical depth variations in the K3 layer, and by the chromospheric temperature stratification. Almost all the fluctuations that are seen with our spatial resolution (approximately 5 arcsec) originate in the high chromospheric K3 layer, while the lower chromospheric layers are much more homogeneous at the resolved scales. The relatively small Q/I fluctuations observed between the K1 and K2 wavelengths constrain the size and lifetime of cold and hot areas in the low and mid chromosphere. Conclusions. At present it is not possible to disentangle the Hanle effect and the hot-spot effect from each other. This would require 2D spatial mapping of the linear polarization at the K3, K2, and Kl wavelengths with higher spatial resolution, which is hard to do with existing telescopes, since the observations are photon starved and require larger telescope apertures.

Center-to-limb-variation of the G-band lines at 430.5 nm

We measure the center-to-limb-variation of the CH lines in the wavelength range from 430.40 to 430.61 nm ( G -band) for both quiet sun and for the cooler atmophere of sunspot umbrae at different heliographic positions. The limb effect of the CH lines is about 650 ms -1 at $\mu=0.1$ with a slope similar to weak Fe lines. We investigate the behaviour of the CH abundance in the range of optical depth ($\tau=-0.05$ to $\tau=-0.25$) that is accessible by center-to-limb observations. The CH abundance decreases with height in accordance with recent numerical models.

Three‐dimensional propagation of coronal mass ejections (CMEs) in a structured solar wind flow: 2. CME launched adjacent to the streamer belt

A three‐dimensional (3‐D) numerical hydrodynamic model is used to investigate the evolution of coronal mass ejections (CMEs) launched at several heliographic positions into a tilted‐dipole ambient solar wind (SW) flow, which is appropriate around solar activity minimum and declining phase. The CME is injected as an overpressured plasma cloud. Results show that the motion and local appearance of a CME in interplanetary space is strongly affected by its interaction with the background SW velocity and density structures. The most complicated scenario occurs when a CME is injected directly into the slow stream‐belt flow. Temporal profiles corresponding to the interaction of fast CME and slow SW flows, to the merging of CME‐driven and corotating disturbances at the fast stream leading edge, and to expanding structures at the trailing edge of the preceding fast stream are presented. The simplest configuration is when a CME is injected just to the west of the streamer belt. In that case the CME‐driven disturbance evolves and propagates freely into the preceding fast stream, untouched by the streamer belt slow flow near which it originates, except for a small segment at low latitudes. When a CME is injected just to the east of the streamer belt, the CME expansion and shock evolution are constrained by the slow, dense flow ahead of the fast stream in which the CME propagates initially. Low‐latitude portions of the CME are trapped between the slow streamer belt flow and the leading edge of the oncoming fast stream. In this case, CME‐driven and corotating shock structures can merge. These results are related to a previous study, where the CME is launched into the midst of the slow streamer belt flow. Numerical results confirm recent Ulysses findings about the overexpanding CME structure, the extreme latitudinal distortions in the CME shape, and the inclination of shock fronts. These results also provide a basis for interpreting variations in the radial width of the CME and the shock stand‐off distance. Simulations of spatial structures resulting from 3‐D dynamic interactions help illuminate differing temporal onsets and profiles of observed CMEs.

On the determination of heliographic positions and rotation velocities of sunspots

On a montre precedemment comment la depression de Wilson influence la determination des vitesses de rotation des taches solaires. A partir de ce fait et que les taches solaires recurentes stables montrent une vitesse de rotation tres constante, il est possible de determiner l'effet d'un rayon de l'image solaire inexact sur la determination des vitesses de rotation des taches solaires et d'effectuer la correction

On the determination of heliographic positions and rotation velocities of sunspots

Using sunspot positions of small sunspots observed at Debrecen and Locarno as well as positions of recurrent sunspots taken from the Greenwich Photoheliographic Results (1940–1976) the influence of the Wilson depression on the rotation velocities was investigated. It was found that the Wilson depression can be determined by minimizing errors of the rotation velocities or minimizing the differences of rotation velocities determined from disk passages and central meridian passages. The Wilson depressions found were between 765 km and 2500 km for the first sample while they were between 0 km and several 1000 km for the second sample. The averaged Wilson depression for the second sample is between 500 km and 965 km depending on the reduction method. A dependence of the Wilson depression on the age of the spots investigated seems not to exist.

On the determination of heliographic positions and rotation velocities of sunspots

On the determination of heliographic positions and rotation velocities of sunspots

On diurnal variations of the solar rotation rate as derived from sunspot tracings

The heliographic positions of more than 100 sunspots were accurately measured several times a day from 1974 until 1979 by means of the computer-controlled tracing method described by Schroter and Wohl (1975). A striking degree of constancy of the solar rotation rate (about 0.15% or 3 m s−1) is found, when east-west proper motion components of each individual stable sunspot is considered. However, large differences of the rotation rate are observed (up to 7% or 130 m s−1) when comparing different sunspots. We found no significant correlation of these fluctuations with characteristics of the sunspots (age, evolution, etc.).

Motions in the solar atmosphere associated with the white light flare of 11 July 1978

Series of white light heliograms and oft- and on-band Hα filtergrams have been obtained, with an average spatial resolution of 1″, to study the flare active McMath region 15403 on 11 July, 1978. A great number of accurate heliographic positions were determined for the umbrae, the white light flare patches and several bright Hα flare knots, as well as along the principal zero filament and an arch prominence. Using the measured heliographic coordinates of these objects their motions could be analyzed in some detail. The velocities of several different objects could be deduced from the coordinates. Since the heliocentric angle of the region was about 45°, the variation in apparent heliographic coordinates also enabled some variations in heights to be determined.

Origin of Solar Radiation in the 1–6 Metre Radio Wave-lenght Band

THE intensity of the solar radiation in the wave-length region of a few metres sometimes deviates extraordinarily from that for a black body at 6000°. The observed departures show a clear correlation with sunspots and their heliographic positions, and become extremely high during the appearance of chromospheric eruptions1. As can be shown, even the intensity of the corona, which will radiate in this spectral region nearly like a black body at 106 degrees, falls short of the observed values.

Direct micrometrical observations of the sun, heliographic positions of sunspots

Direct micrometrical observations of the sun, heliographic positions of sunspots

Heliographic Positions. I

Heliographic Positions. I