Xenophon Moussas

Motivated by the construction of the Monumental Antikythera Mechanism for Hermosillo and its future exhibition at the “Centro” campus of the Universidad de Sonora, Mexico, we undertook a study about the prediction of eclipses, implemented in this mechanism whose basis is the knowledge of the Saros Cycle. It was natural, to arrive at the need to add to this study, the Mesoamerican perspective of eclipses; in particular, we arrive at the analysis of the Table of Eclipses of the Dresden Codex. It was from the sequence of intervals of this table, which we decided to make a comparison between both perspectives: the Maya of the Dresden Codex and the Greek of the Saros Cycle. In this report we present our findings and contrast their main properties. In Maya case: The prediction of solar eclipses could be obtained from systematic observations of the Moon because, in the introductory section of the table (pages 51a and 52a), there are elements for elaboration of the sequence of 69 eclipses reported from pages 53a to 58b; The period of 11,960 days (11,958 in the sequence) allowed them to group solar eclipses according to their type by groups of 7 or 9; The ten vignettes after the 148-day intervals could be attributed to eclipses observed in the Maya zone; and, when comparing the sequence of eclipses in the table with the sequence of eclipses that occurred in the span of 700 to 800 CE, the series identified by the eclipse of 06/08/0788 was the series of greater coincidence. On the side of the Saros we have: the eclipses are recorded in the corresponding spiral of the mechanism and there are 27 solar eclipses; Each eclipse appears with date and time of occurrence by means of the spiral and the glyphs in it; in the period of 19,755 days (3 Saros = 3 X 6585 days = 1 Exeligmus) an eclipse occurs again at the same geographical longitude; Those reported are eclipses observed in the area of the mechanism going from partial to annular and, finally, to total and vice versa. These findings suggest that the Maya must have had a model of theWorld in which the Earth, Moon and Sun had a specific role to play in eclipses; and, consequently, they must have had a comprehensive model of their own.

We studied 2204 sympathetic flares detected by the GOES during 1975–2017. Sympathetic flares have nearby, or homogeneous, GOES classes. The secondary solar flare is just a mirror image of the primary solar flare of the sympathetic flare. It has two types: 1) Twins: This type represents most of them (∼78.6%). 2) Non-twins: It is an associated heterogeneous pair of solar flares. A negative relationship between the interval between the start times of primary and secondary flares was found with the duration of the primary flare with the solar cycle progress. Also, the stronger the solar cycle, the lower the maximum value of the timing ratio at the quiet Sun’s epoch, while the timing ratio’s value reaches a higher value during the weaker cycles. A positive relationship between the angular distance between pairs of sympathetic flares and SSN has been found. During the epoch of the active sun, the distance is as far as possible, while that distance becomes shorter during the epoch of the quiet sun. Sympathetic flares are equatorial in alignment. The higher inclination (slope of about −20° each cycle) is associated with the X-Class of the primary flare. It is more than this non-association. We found that the time series of inclinations is given a “Wings diagram” diagram.

We have studied the variation of the time profile of X-ray emission of solar flares that occurred during the second half of solar cycle 23 (SC 23) and for about the full solar cycle 24 (SC 24) (2002–2018). We define a new index, called the “ratio index” (R_f), for all X-ray solar flares. This index is defined as the ratio of the flare’s rising time interval by its total duration period. According to the ratio index, the X-ray solar flares are classified into two types: (1) sudden flares [R_f < 0.5], and (2) gradual flares [R_f > 0.5]. The sudden flare type, with fast-rising and slow recovery, is more common and represents most of the flares that happen most of the time during the solar cycles but are less common during the minimum solar activity years. On the other hand, the gradual flare type (or R_f > 0.5) is less common but predominates during the minimum solar activity epochs. Sudden flares tend to be strong, large, and numerous in the polar regions, while gradual flares are weak, short, and countable in the latitude range between 50 and 70, both for northern and southern latitudes. However, both types appear to happen in the lower latitudes and the solar equatorial regions.

Aims. We examine high time resolution dynamic spectra for fine structures in type II solar radio bursts Methods. We used data obtained with the acousto-optic spectrograph receiver of the Artemis-JLS (ARTEMIS-IV) solar radio spectrograph in the 450–270 MHz range at 10 ms cadence and identified more than 600 short, narrowband features. Their characteristics, such as instantaneous relative bandwidth and total duration were measured and compared with those of spikes embedded in type IV emissions. Results. Type II associated spikes occur mostly in chains inside or close to the slowly drifting type II emission. These spikes coexist with herringbone and pulsating structures. Their average duration is 96 ms and their average relative bandwidth 1.7%. These properties are not different from those of type IV embedded spikes. It is therefore possible that they are signatures of small-scale reconnection along the type II shock front.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics