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Register a new userThe Comets of Caroline Herschel (1750-1848), Sleuth of the Skies at Slough
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In this paper, we discuss the work on comets of Caroline Herschel, the first female comet-hunter. After leaving Bath for the environs of Windsor Castle and eventually Slough, she discovered at least eight comets, five of which were reported in the Philosophical Transactions of the Royal Society. We consider her public image, astronomers perceptions of her contributions, and the style of her astronomical drawings that changed with the technological developments in astronomical illustration.
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This is a translation from Latin of E840 De motu cometarum in orbitis parabolicis, solem in foco habentibus, in which Euler addresses six problems related to comets in heliocentric parabolic orbits. Problem 1: Find the true anomaly of a heliocentric comet from the latus rectum of the orbit and the medium Earth to Sun distance. Problem 2: Find the orbit of a heliocentric comet from three given positions. Problem 3: Knowing the orbit of a comet, and the instant in time in which it dwells in the perihelion, define its longitude and latitude at any time. Problem 4: From two locations of a heliocentric comet, find the inclination of the comets orbit in relation to the ecliptic, and the positions of the nodes. Problem 5: From the time before or after the comet had reached the perihelion, and from the comets distance to the perihelion as seen from the Sun, find the same distance in another time before or after it had appeared in the perihelion. Problem 6: Find the orbit of a comet from three given heliocentric longitudes and latitudes. From these problems, several corollaries and scholia are derived.
An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck with the period of 2.850 days. Previous astronomical, astrophysical and statistical analyses of CC support the idea that this was the period of the eclipsing binary Algol three millennia ago. However, next to nothing is known about who recorded Algols period into CC and especially how. Here, we show that the ancient Egyptian scribes had the possible means and the motives for such astronomical observations. Their principles of describing celestial phenomena as activity of gods reveal why Algol received the title of Horus.
Eirene Laskarina, empress of John III Batatzes of the exiled Byzantine Empire of Nicaea (1204--1261 CE), was an important Eastern Mediterranean figure in the first half of the thirteenth century. We reassess the date of Eirenes death, which has been variously dated between late 1239 and 1241, with the understanding that narrowing the range in which this event occurred contributes much to understanding the political situation in the area around 1240. George Akropolites, a famous official of the Empire, gives an account that connects Eirenes death to a comet that appeared six months earlier, thus pointing to two comet candidates that were visible from the Eastern Mediterranean between 1239 and 1241, one recorded on 3 June 1239 and the other on 31 January 1240. Recent historians prefer the former, based on historical circumstances and without a critical assessment of the comet records. We revisit the historical records and reveal that the 3 June 1239 candidate was not a comet. On the other hand, the other candidate, sighted on 31 January 1240, was a comet, as supported by multiple historical records in multiple regions, and is also a good fit with Akropolitess narrative. Therefore, we conclude that Eirene died six months after the comet that was seen on 31 January 1240, which places her death in the summer of 1240. Given that the date of her death is crucial for determining some other contemporary events across the Eastern Mediterranean, our results offer a solid basis for further research on the thirteenth-century Eastern Mediterranean.
Given that a strong 14C variation in AD 775 has recently been suggested to be due to the largest solar flare ever recorded in history, it is relevant to investigate whether celestial events observed around that time may have been aurorae, possibly even very strong aurorae, or otherwise related to the 14C variation (e.g. a suggested comet impact with Earths atmosphere). We critically review several celestial observations from AD 757 to the end of the 770s, most of which were previously considered to be true, and in some cases, strong aurorae; we discuss in detail the East Asian records and their wording. We conclude that probably none among the events after AD 770 was actually an aurora, including the event in AD 776 Jan, which was misdated for AD 774 or 775; the observed white qi phenomenon that happened above the moon in the south-east was most probably a halo effect near the full moon - too late in any case to be related to the 14C variation in AD 774/5. There is another report of a similar (or identical) white qi phenomenon above the moon, reported just before a comet observation and dated to AD 776 Jan; the reported comet observed by the Chinese was misdated to AD 776, but actually sighted in AD 767. Our critical review of East Asian reports of aurorae circa AD 775 shows some very likely true Chinese auroral displays observed and reported for AD 762; there were also several events prior to AD 771 that may have been aurorae but are questionable.
Comparing the number of clear nights (cloud free) available for astronomical observations is a critical task because it should be based on homogeneous methodologies. Current data are mainly based on different judgements based on observer logbooks or on different instruments. In this paper we present a new homogeneous methodology on very different astronomical sites for modern optical astronomy, in order to quantify the available night time fraction. The data are extracted from night time GOES12 satellite infrared images and compared with ground based conditions when available. In this analysis we introduce a wider average matrix and 3-Bands correlation in order to reduce the noise and to distinguish between clear and stable nights. Temporal data are used for the classification. In the time interval 2007-2008 we found that the percentage of the satellite clear nights is 88% at Paranal, 76% at La Silla, 72.5% at La Palma, 59% at Mt. Graham and 86.5% at Tolonchar. The correlation analysis of the three GOES12 infrared bands B3, B4 and B6 indicates that the fraction of the stable nights is lower by 2% to 20% depending on the site.
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