Papers – Page 7 – British Astronomical Association

British Isles aurorae, 1560–1715, Part II: 1645–1715

This is the second of two papers in which, together, 28 previously unrecognised cases of probable aurorae seen in the

HR Lyrae: the restless slumbers of an old nova

A report of the Variable Star Section. Director: J. Shears. We present the light curve of the old nova

Figure 3. Different observations arranged according to the decreasing position angle of the location along the lunar limb that is maximally tilted towards Earth. Details of the equipment used are given in the text. The peaks of Montes d’Alembert are subdivided into a northern group (red brackets) and a southern group (white brackets). North is up.

Identifying the peaks of Montes d’Alembert

The Montes d’Alembert are a chain of mountain peaks found along the western lunar limb. The individual mountains were grouped

Figure 2. WAC image of the examined region. Note the dome Lavoisier 4, which is not prominent as in the telescopic image (Figure 1). The image is shown in cylindrical projection, removing the foreshortening.

Lunar domes near Lavoisier K

In this study, we examine four lunar domes located near the crater Lavoisier K. The large domes, termed Lavoisier 1–3,

British Isles aurorae, 1560–1715, Part I: 1560–1644

This is the first of two papers in which, together, 28 previously unrecognised cases of probable aurorae seen in the

R CrA & cyclic brightness variations in NGC 6729

An indicative unfiltered light curve has been generated for the protostar R CrA. During the period 2018 May to 2020 November, the variability was seen to be substantial (11.5–13.1), but only weakly compliant with the 65.7-day variability generally attributed to R CrA. The star illuminates the fan-shaped NGC 6729 nebula. Variability in the nebula was observed to begin close to R CrA and then move steadily down the fan, fading as it progressed. Measurements of the surface brightness of the different parts of the nebula showed an apparent relationship in the delay between brightening of R CrA and the subsequent brightening of parts of the fan. These variations appear consistent with light echoes.

Jupiter in 1949 & the Revival of the South Equatorial Belt

Until now there has never been a comprehensive account of Jupiter’s 1949 apparition, in which there was a Revival of the South Equatorial Belt (SEB). On opposition day, Jul 19, despite the SEB south component not having faded to invisibility, the first white spot of the Revival was seen. The spot had originated within a pre-existing SEB(S) dark ‘barge’, close to the longitude of E. J. Reese’s ‘Source B’. The Revival led to a fading of the initially conspicuous Great Red Spot (GRS), and the development of the Red Spot Hollow (RSH). The S. branch of the Revival was weak, with small retrograding dark spots which failed to pass the GRS, although their velocity was typical. The N. branch was also less active, with some prograding dark spots passing only slightly beyond the GRS/RSH, which also exhibited a typical drift. On the other hand, the central branch was unusually active, with a succession of long-lived white spots and dark columns (mean drift rate Δλ2 = –67°/30 days). The p. end of the Disturbance in …

Multiwavelength observation of polar faculae

By observing the polar regions of the Sun on three occasions and in three wavebands, polar faculae in the photosphere were studied and compared to features found in the chromosphere at wavelengths of calcium II K and hydrogen-alpha. It was found that the white-light polar faculae are closely associated with calcium II K bright plage, but more tenuously associated with hydrogen-alpha plage. Associations were more consistent for hydrogen-alpha mottles, although non-specific correlations could not be excluded.

Figure 1. The Great Sunspot of 1947 (Greenwich group number 14886). Photograph from the Royal Observatory, Greenwich, 1947 Apr 7. (See ref. 7.)

The five greatest sunspot groups

Remarkably, the five largest recorded sunspot groups all occurred during a period of just over five years, from 1946 February to 1951 May, during Solar Cycle 18. These are the only groups known with areas greater than 4,500 millionths of the Sun’s visible hemisphere. This paper examines the white-light activity of the groups.

Five thousand years of Jupiter–Saturn conjunctions

The recent so-called ‘Great Conjunction’ of Jupiter and Saturn, in 2020 December, was the latest in a series of conjunctions of the two planets that occur, on average, every 19.67 years. Although events between Jupiter and Saturn are visually not the most spectacular of conjunctions, they are of great historical interest due to the triple conjunction that occurred around the time of the Nativity, which authors such as Hughes (1976) have associated with the Star of Bethlehem. A total of 309 Jupiter–Saturn conjunctions are found between 1000 BC and AD 4000, which include 84 grouped in 28 triple conjunctions. The 2020 conjunction is found to be in the top five percent of closest approaches of the two planets over five millennia. The closest conjunctions show a strong preference for occurring in Cancer in July/August, or Capricornus in December.