arXiv subjects

J. M. Vaquero

Publications and source records attributed to J. M. Vaquero.

At least 37 records · Page 2Linked to original sources

arXiv2018

The Great Aurora of January 1770 observed in Spain

An analysis is made of the records made by Spanish observers of a notable aurora on 18 January 1770 in order to study the characteristics of this event. The records indicate that the phenomenon was observed in both continental and insular territories of Spain, in particular at San Cristóbal de la Laguna, Cádiz, Córdoba, Badajoz, Valencia, Castellón, Madrid, Barcelona, and Gerri de la Sal. The most equatorward observational site was San Cristóbal de la Laguna (28.48° N, 16.32° W) in the Canary Islands. In general, the descriptions put its duration from sunset to midnight, but the observers from Córdoba and Madrid report the aurora as being visible during the last hours of the night, and it was even observed the following day at Castellón. All the observers described the aurora as red in colour, while white and ash colours were also reported at Córdoba and Gerri de la Sal. The brightness and shape of auroral display changed over time. Calculations of the geomagnetic latitudes of the observation locations gave San Cristóbal de la Laguna as the southernmost (26° N) to Gerri de la Sal the northernmost (35° N), and indicate this aurora was observed over a wide range of abnormally low latitudes for such a phenomenon. Solar activity around the event was high, with the astronomer Horrebow registering 10 sunspot groups on that date (18 January 1770).

physics.hist-ph↗

arXiv2018

The umbra-penumbra area ratio of sunspots during the Maunder Minimum

The Maunder Minimum (MM) was a prolonged period of low solar activity that occurred between 1645 and 1715. The true level of solar activity corresponding to this epoch is still a matter of debate. In order to compare solar activity during the MM with that of other epochs, we have evaluated the umbra-penumbra area ratio (U/P hereafter) during the MM. Thus, we have analyzed 196 sunspot drawings including 48 different sunspots observed during the period 1660-1709. The mode value of the ratio obtained from the occurrence frequency distribution lies between 0.15 and 0.25. Furthermore, the median and mean values are equal to 0.24 \pm 0.07 and 0.27 \pm 0.08 with a sigma clipping, respectively. These results are consistent with recent research using more modern data. Higher U/P values mean faster sunspot decay rates. From our results, the almost absence of sunspots during the Maunder Minimum could not be explained by changes in the U/P since the values of the ratio obtained in this work are similar to values found for other epochs.

astro-ph.SR↗

arXiv2018

Sunspot Observations Made by Hallaschka during the Dalton Minimum

We present and analyse the sunspot observations performed by Franz I. C. Hallaschka in 1814 and 1816. These solar observations were carried out during the so-called Dalton minimum, around the maximum phase of the Solar Cycle 6. These records are very valuable because they allow us to complete observational gaps in the collection of sunspot group numbers, improving its coverage for this epoch. We have analysed and compared the observations made by Hallaschka with the records made by other contemporary observers. Unfortunately, the analysis of the sunspot areas and positions showed that they are too inaccurate for scientific use. But, we conclude that sunspot counts made by Hallaschka are similar to those made by other astronomers of that time. The observations by Hallaschka confirm a low level of the solar activity during the Dalton minimum.

astro-ph.SR↗

arXiv2018

A Curious History of Sunspot Penumbrae: An Update

The ratio of penumbral to umbral area of sunspots is an important topic for solar and geophysical studies. Hathaway (Solar Physics, 286, 347, 2013) found a curious behaviour in this parameter for small sunspot groups (areas smaller than 100 millionths of solar hemisphere, msh) using records from Royal Greenwich Observatory (RGO). Hathaway showed that penumbra-umbra ratio decreased smoothly from more than 7 in 1905 to lower than 3 by 1930 and then increased to almost 8 in 1961. Thus, Hathaway proposed the existence of a secular variation in the penumbra-umbra area ratio. In order to confirm that secular variation, we employ data of the sunspot catalogue published by the Coimbra Astronomical Observatory (COI) for the period 1929-1941. Our results disagree with the penumbra-umbra ratio found by Hathaway for that period. However, the behaviour of this ratio for large (areas greater or equal than 100 msh) and small groups registered in COI during 1929-1941 is similar to data available from RGO for the periods 1874-1914 and 1950-1976. Nevertheless, while the average values and time evolution of the ratio in large groups is similar to the ratio for small groups according to Coimbra data (1929-1941) it is not analogous for RGO data for the same period. We also found that the behaviour of the penumbra-umbra area ratio for smaller groups in both observatories is significantly different. The main difference between the area measurements made in Coimbra and RGO is associated with the umbra measurements. We would like to stress that the two observatories used different methods of observation and while in COI both methodology and instruments did not change during the study period, some changes were carried out in RGO that could have affected measurements of umbra and penumbra. These facts illustrate the importance of the careful recovery of past solar data.

astro-ph.SR↗

arXiv2018

Early solar photographs by G. Roster (April 1893)

There are relatively few antique photographs of the Sun compared to drawings of the solar disc. We want to highlight three solar photographs taken by Giorgio Roster in 1893. Roster (1843-1894) was a doctor, chemist, and photographer. The library of the Museo di storia della scienza of Florence preserves part of Roster's legacy in the section "Carte e raccolta fotografica Roster", in which we want to highlight the title "Telefotografie Roster V: Macchie solari; teleobiettivo Roster, 1892-1893". This title contains three solar photographs taken from Florence with a Roster tele-objective. The main characteristics of the three photographs are: (i) Date: 21st April 1893. Time: 5:15 p.m. Magnification: 61x. (ii) Date: 25th April 1893. Time: 4:40 p.m. Magnification: 68x. (iii) Date: 30th April 1893. Time: 17:00 p.m. Magnification: 71x. It may be interesting to note that, although there are drawings of the solar disc in the collection of the Kalocsa Observatory for the days 21 and 30, there is no such thing for day 25. Thus, Roster's photographs fill that gap in the graphical information of the Sun.

physics.hist-ph↗

arXiv2018

Could a Hexagonal Sunspot Have Been Observed During the Maunder Minimum?

The Maunder Minimum was the period between 1645 and 1715 whose main characteristic was abnormally low and prolonged solar activity. However, some authors have doubted this low level of solar activity during that period by questioning the accuracy and objectivity of the observers. This work presents a particular case of a sunspot observed during the Maunder Minimum with an unusual shape of its umbra and penumbra: a hexagon. This sunspot was observed by Cassini in November 1676, just at the core of the Maunder Minimum. This historical observation is compared with a twin case that occurred recently in May 2016. The conclusion reached is that Cassini's record is another example of the good quality observations made during the Maunder Minimum, showing the meticulousness of the astronomers of that epoch. This sunspot observation made by Cassini does not support the conclusions of Zolotova and Ponyavin (Astrophys. J. 800, 42, 2015) that professional astronomers in the 17th century only registered round sunspots. Finally, a discussion is given of the importance of this kind of unusual sunspot record for a better assessment of the true level of solar activity in the Maunder Minimum.

astro-ph.SR↗

arXiv2018

Extreme value theory applied to the millennial sunspot number series

In this work, we use two decadal sunspot number series reconstructed from cosmogenic radionuclide data (14C in tree trunks, SN-14C and 10Be in polar ice, SN-10Be) and the Extreme Value Theory to study variability of solar activity during the last 9 millennia. The peaks-over-threshold technique was used to compute, in particular, the shape parameter of the generalized Pareto distribution for different thresholds. Its negative value implies an upper bound of the extreme SN-10Be and SN-14C time series. The return level for 1000 and 10000 years were estimated leading to values lower than the maximum observed values, expected for the 1000-year, but not for the 10000-year return levels, for both series. A comparison of these results with those obtained using the observed sunspot numbers from telescopic observations during the last four centuries suggest that the main characteristics of solar activity have already been recorded in the telescopic period (from 1610 to nowadays) which covers the full range of solar variability from a Grand minimum to a Grand maximum.

astro-ph.SR↗

arXiv2017

Analysing the spotless days as predictors of the solar activity from the new sunspot number

The use of the spotless days to predict the future solar activity is here revised based on the new version of the sunspot number index with a 24-month filter. Data from Solar Cycle (SC) 10 are considered because from this solar cycle the temporal coverage of the records is 100 %. The interrelationships of the timing characteristics of spotless days and their comparison with sunspot cycle parameters are explored, in some cases finding very strong correlations. Such is the case for the relationship between the minimum time between spotless days either side of a given solar maximum and the maximum time between spotless days either side in the previous solar minimum, with r = -0.91 and a p-value < 0.001. However, the predictions for SC 24 or 23 made by other authors in previous works using the spotless days as a predictor of solar activity are not good since it has not been fulfilled. Although there seems to be a pattern of strong correlation for some relationships between the parameters studied, prediction of future solar cycles from these parameters defined as functions of the spotless days should be made with caution because sometimes the estimated values are far from the observed ones. Finally, SC 23 seems to show a mode change, a break respect to the behavior of their previous solar cycles and more similar to SC 10-15.

astro-ph.SR↗

arXiv2017

The sunspot observations by Toaldo and Comparetti at November 1779

There is a low frequency of sunspot observations in some years of the 17th and 18th century. In particular, the interval 1777-1795 is one of the periods with scarce observations in the databases. In this note, we report a sunspot observation carried out the 3rd November 1779 by Giuseppe Toaldo and Andrea Comparetti.

astro-ph.SR↗

arXiv2017

Unusual rainbows as auroral candidates: another point of view

Several auroral events that occurred in the past have not been catalogued as such due to fact that they were described in the historical sources with different terminology. Hayakawa et al. (2016) have reviewed historical oriental chronicles and have proposed the terms "unusual rainbow" and "white rainbow" as candidates to auroras. In this work, we present three events that took place in the 18th century in two different settings (the Iberian Peninsula and Brazil) that were originally described with similar definition/wording used by the oriental chronicles, despite the inherent differences in terms associated to oriental and Latin languages. We show that these terms are indeed applicable to the three case studies from Europe and South America. Thus, the auroral catalogues available can be extended for occidental sources with this new terminology.

astro-ph.SR↗

arXiv2017

Evidence for a White-light Flare on 10 September 1886

We present evidence for the occurrence of a white-light flare on 10 September 1886. It represents the third of such rare events reported in the history of astronomy. The flare was mentioned by Valderrama (1886, L'Astronomie 5, 388). In this article we have used the original logbook of the observer, J. Valderrama y Aguilar, an amateur astronomer that lived in Madrid and Santa Cruz de Tenerife at that time.

astro-ph.SR↗

arXiv2016

A Revised Collection of Sunspot Group Numbers

We describe a revised collection of the number of sunspot groups from 1610 to the present. This new collection is based on the work of Hoyt and Schatten (Solar Phys. 179, 189, 1998). The main changes are the elimination of a considerable number of observations during the Maunder Minimum (hereafter, MM) and the inclusion of several long series of observations. Numerous minor changes are also described. Moreover, we have calculated the active-day percentage during the MM from this new collection as a reliable index of the solar activity. Thus, the level of solar activity obtained in this work is greater than the level obtained using the original Hoyt and Schatten data, although it remains compatible with a grand minimum of solar activity. The new collection is available in digital format.

astro-ph.SR↗

arXiv2016

Revisiting the prediction of solar activity based on the relationship between the solar maximum amplitude and max-max cycle length

It is very important to forecast the future solar activity due to its effect on our planet and near space. Here, we employ the new version of the sunspot number index (version 2) to analyse the relationship between the solar maximum amplitude and max-max cycle length proposed by Du (2006). We show that the correlation between the parameters used by Du (2006) for the prediction of the sunspot number (amplitude of the cycle, Rm, and max-max cycle length for two solar cycles before, Pmax-2) disappears when we use solar cycles prior to solar cycle 9. We conclude that the correlation between these parameters depends on the time interval selected. Thus, the proposal of Du (2006) should definitively not be considered for prediction purposes.

astro-ph.SR↗

arXiv2016

A Normalized Sunspot-Area Series Starting in 1832: an Update

A new normalized sunspot-area series has been reconstructed from the series obtained by the Royal Greenwich Observatory and other contemporary institutions for the period 1874 - 2008 and the area series compiled by De la Rue, Stewart, and Loewy from 1832 to 1868. Since the two sets of series do not overlap in time, we used as a link between them the new version of sunspot index number (Version 2) published by SILSO (Sunspot Index and Long-term Solar Observations). We also present a spectral analysis of the normalized area series in search of periodicities beyond the well-known solar cycle of 11 years and a study of the Waldmeier effect in the new version of sunspot-number and the sunspot-area series presented in this study. We conclude that while this effect is significant in the new series of sunspot number, it has a weak relationship with the sunspot-area series.

astro-ph.SR↗

arXiv2016

Monitoring the Solar Radius from the Royal Observatory of the Spanish Navy during the Last Quarter-Millennium

The solar diameter has been monitored at the Royal Observatory of the Spanish Navy (today the Real Instituto y Observatorio de la Armada: ROA) almost continuously since its creation in 1753 (i.e. during the last quarter of a millennium). After a painstaking effort to collect data in the historical archive of this institution, we present here the data of the solar semidiameter from 1773 to 2006, making up an extensive new database for solar-radius measurements can be considered. We have calculated the solar semidiameter from the transit times registered by the observers (except values of the solar radius from the modern Danjon astrolabe, which were published by ROA). These data were analysed to reveal any significant long-term trends, but no such trends were found. Therefore, the data sample confirms the constancy of the solar diameter during the last quarter of a millennium (approximately) within instrumental and methodological limits. Moreover, no relationship between solar radius and the new sunspot-number index has been found from measurements of the ROA. Finally, the mean value for solar semidiameter (with one standard deviation) calculated from the observations made in the ROA (1773-2006), after applying corrections by refraction and diffraction, is equal to 958.87" \pm 1.77"

astro-ph.SR↗

arXiv2016

Sunspot group tilt angle measurements from historical observations

Sunspot positions from various historical sets of solar drawings are analysed with respect to the tilt angles of bipolar sunspot groups. Data by Scheiner, Hevelius, Staudacher, Zucconi, Schwabe, and Spoerer deliver a series of average tilt angles spanning a period of 270 years, 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 50 years 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.

astro-ph.SR↗

arXiv2016

Sunspot Observations during the Maunder Minimum from the Correspondence of John Flamsteed

We compile and analyze the sunspot observations made by John Flamsteed for the period 1672-1703, corresponding to the second part of the Maunder Minimum, which appear in the correspondence of this famous astronomer. We include in an appendix the original texts of the sunspot records kept by Flamsteed. We compute an estimate of the level of solar activity using these records, and compare the results with the latest reconstructions of solar activity during the Maunder Minimum, obtaining values characteristic of a grand solar minimum. Finally, we discuss a phenomenon observed and described by Stephen Gray in 1705 that has been interpreted as a white-light flare.

astro-ph.SR↗

arXiv2015

Equivalence relations between the Cortie and Zurich sunspot group morphological classifications

Catalogues of sunspots have been available with useful information about sunspots or sunspot groups for approximately the last 150 years. However, the task of merging these catalogues is not simple. In this paper, a method is suggested of converting the types of sunspot groups that were proposed by Cortie (1901) into the well-known Zurich types of sunspot groups. To achieve this, the sunspot catalogue of the Valencia University Observatory (from 1920 to 1928) was used in addition to the descriptions proposed by Cortie. To assess the quality of this conversion scheme, the Zurich type was computed from the Valencia catalogue, and the resulting contribution of each group type was compared to what can be found in other catalogues. The results show that the proposed scheme works well within the errors that are found in the different catalogues.

astro-ph.SR↗