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 Earth's 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.Comment: 15 pages with 4 figure

The strong 14C increase in the year AD 774/5 detected in one German and two Japanese trees was recently suggested to have been caused by an impact of a comet onto Earth and a deposition of large amounts of 14C into the atmosphere (Liu et al. 2014). The authors supported their claim using a report of a historic Chinese observation of a comet ostensibly colliding with Earth's atmosphere in AD 773 January. We show here that the Chinese text presented by those authors is not an original historic text, but that it is comprised of several different sources. Moreover, the translation presented in Liu et al. is misleading and inaccurate. We give the exact Chinese wordings and our English translations. According to the original sources, the Chinese observed a comet in mid January 773, but they report neither a collision nor a large coma, just a long tail. Also, there is no report in any of the source texts about "dust rain in the daytime" as claimed by Liu et al. (2014), but simply a normal dust storm. Ho (1962) reports sightings of this comet in China on AD 773 Jan 15 and/or 17 and in Japan on AD 773 Jan 20 (Ho 1962). At the relevant historic time, the Chinese held that comets were produced within the Earth's atmosphere, so that it would have been impossible for them to report a "collision" of a comet with Earth's atmosphere. The translation and conclusions made by Liu et al. (2014) are not supported by the historical record. Therefore, postulating a sudden increase in 14C in corals off the Chinese coast precisely in mid January 773 (Liu et al. 2014) is not justified given just the 230Th dating for AD 783 \pm 14.Comment: 4 pages with one figure, paper in press in Astronomical Notes 201

Galactic novae and supernovae can be studied by utilizing historical observations, yielding explosion time, location on sky etc. Recent publications by Hoffmann & Vogt present CVs, supernova remnants, planetary nebulae etc. as potential counterparts based on their list of historically reported transients from the Classical Chinese text corpus. Since their candidate selection neglects the state-of-the-art (e.g. Stephenson & Green), and since it includes ‘broom stars’ and ‘fuzzy stars’, i.e. probable comets, we investigate their catalogue in more detail. We discuss here their two highlights, the suggestion of two ‘broom star’ records dated AD 667 and 668 as one historical supernova and of the ‘guest star’ of AD 891 as recurrent nova U Sco. The proposed positional search areas are not justified due to translation and dating problems, source omission, as well as misunderstandings of historical Chinese astronomy and unfounded textual interpretations. All sources together provide strong evidence for comet sightings in both AD 668 and 891 – e.g., there are no arguments for stationarity. The AD 667 record is a misdated doublet of 668. Our critique pertains more generally to their whole catalogue of ‘24 most promising events’: their speculations on counterparts lack a solid foundation and should not be used in follow-ups.

Recent advances in techniques of critical close reading of historical texts can now be applied to records of pre-telescopic celestial observations -allowing significant progress for analyzing and solving orbits of past comets: here, as a blueprint test case, we exemplify our method by solving the orbit of the comet in AD 760 only with historical observations and then identify it with 1P/Halley. A detailed eyewitness record with drawing of a comet in AD 760 in the Syriac Chronicle of Zuqnīn (finished AD 775/6) was not yet included in the study of its orbit -the Chinese reports alone do not yield a sufficient number of dated positions. We analyze the Syriac and Chinese sources with critical methods for quantitative astronomical usage, we also consider a few further records from the Mediterranean and West Asian area. With our conservatively derived dated positions we can determine the best fitting Keplerian orbital solution by least squares fitting yielding the orbital elements ( 2 red < 2 based on 1 million runs); the parameter ranges for non-periodic solutions and highly eccentric periodic solutions are consistent with each other. The allowed parameter ranges for perihelion distance and inclination are sufficiently small to identify the comet with 1P/Halley. Although 1P/Halley is the only comet, where the telescopic orbit is credibly linked to pre-telescopic returns, e.g. to AD 760, our identification confirms claims from extrapolating telescopic observations backward in time -here independently based on historical data. In particular, we obtained a precise perihelion time (AD 760 May 19.1 ± 1.7). The inferior conjunction between comet and Sun as on the previously published orbit (AD 760 May 31.9, Yeomans & Kiang 1981) is shifted by about one day compared to our new orbit (June 1.8), only the new one is consistent with the last observation (June 1.0) before conjunction as reported in the Chronicle of Zuqnīn. Such a precision would be most critical for studying nongravitational forces on comets. By studying the comet's brightness evolution, we also compute its absolute brightness and activity parameter for AD 760 and found indications that the comet was quite dusty that year. As the last return before a close encounter with Earth in AD 837, the AD 760 perihelion is particularly important for extrapolation further back in time (at AD 837 and 800, Yeomans & Kiang 1981 had to introduce corrections in their standard orbit). Our improved methods developed in a multidisciplinary cooperation offer possibilities also to solve more orbits and to identify more comets from the rich and widespread pre-telescopic transmissions.

. However, we show strong shortcomings in the digital search technique as applied by them: almost all likely true sunspot and aurora records were presented earlier (e.g., Xu et al. 2000), which are not mentioned in those papers; the remaining records are dubious and often refer to other phenomena, neither spots nor aurorae (this also applies to Hayakawa et al. 2017c). The alleged aurorae in Hayakawa et al. (2015) and Kawamura et al. (2016) show a broad peak around full moon, not expected for aurorae. Hayakawa et al. (2017a) use the Korean report At night, the gate of heaven was opened (between AD 992 Dec 6 and AD 993 Jan 25, i.e., close to the 14 C variation AD 993/994) to estimate the Dst index of solar activity, even though the text does not fulfill any discriminative aurora criteria (except night-time). Most of the above publications include very few Chinese texts and translations, and their tables with abbreviated keywords do not allow the reader to consider alternative interpretations (the tables also do not specify which records mention night-time). We have compared some of their event tables with previously published catalogues and found various discrepancies. There are also intrinsic inconsistencies, misleading information (lunar phase for day-time events), and dating errors. We present Chinese texts and translations for some of their presumable new aurorae: only one can be considered a likely true aurora (AD 604 Jan); some others were selected on the sole basis of the use of the word light or rainbow. Several alleged new aurorae present observations beside the Sun during day-time. There are well-known comets among their presumable aurorae. We also discuss (a) whether heiqi ri pang can stand for black spot(s) on one side of or beside the sun, (b) the aurora color confusion in Hayakawa et al. (2015Hayakawa et al. ( , 2016, and (c) whether white and unusual rainbows can be aurorae.

The recently published Yemeni observation report about SN 1006 from al‐Yamānī clearly gives AD 1006 April 17 ± 2 (mid‐Rajab 396h) as the first observation date. Since this is ∼1.5 weeks earlier than the otherwise earliest reports (April 28 or 30) as discussed so far, we were motivated to investigate an early sighting in more depth. We searched for additional evidences from other areas like East Asia and Europe. We found that the date given by al‐Yamānī is fully consistent with other evidence, including the following: (a) SN 1006 rose several times half an hour after sunset (al‐Yamānī), which is correct for the location of Ṣancā' in Yemen for the time around April 17, but it would not be correct for late April or early May. (b) The date (third year, third lunar month, 28th day wuzi, Ichidai Yoki) for an observation of a guest star in Japan is inconsistent (there is no day wuzi in that lunar month), but may be dated to April 16 by reading a wuwu date rather than a wuzi date. (c) There is observational evidence that SN 1006 was observed in East Asia in early or mid‐April; for the second half of April, a bad weather (early monsoon) period is not unlikely— there is a lack of night reports. (d) The observer in St. Gallen reported to have seen SN 1006 for 3 months, which must have ended at the very latest on AD 1006 July 10, given his northern location, so that his observations probably started in April. We conclude that the correctly reported details give quite high confidence in the fully self‐consistent report of al‐Yamānī, so that the early discovery date should be considered seriously.

After core hydrogen burning, massive stars evolve from blue-white dwarfs to red supergiants by expanding, brightening, and cooling within few millennia. We discuss a previously neglected constraint on mass, age, and evolutionary state of Betelgeuse and Antares, namely their observed colour evolution over historical times: We place all 236 stars bright enough for their colour to be discerned by the unaided eye (V≤3.3 mag) on the colour-magnitude-diagram (CMD), and focus on those in the Hertzsprung gap. We study pre-telescopic records on star colour with historically-critical methods to find stars that have evolved noticeably in colour within the last millennia. Our main result is that Betelgeuse was recorded with a colour significantly different (non-red) than today (red, B−V=1.78 ± 0.05 mag). Hyginus (Rome) and Sima Qian (China) independently report it two millennia ago as appearing like Saturn (B−V=1.09 ± 0.16 mag) in colour and ‘yellow’ (quantifiable as B−V=0.95 ± 0.35 mag), respectively (together, 5.1σ different from today). The colour change of Betelgeuse is a new, tight constraint for single-star theoretical evolutionary models (or merger models). It is most likely located less than one millennium past the bottom of the red giant branch, before which rapid colour evolution is expected. Evolutionary tracks from MIST consistent with both its colour evolution and its location on the CMD suggest a mass of ∼14M⊙ at ∼14 Myr. The (roughly) constant colour of Antares for the last three millennia also constrains its mass and age. Wezen was reported white historically, but is now yellow.

However, we show strong shortcomings in the digital search technique as applied by them: almost all likely true sunspot and aurora records were presented before (e.g. Xu et al. 2000), which is not mentioned in those papers; the remaining records are dubious and often refer to other phenomena, neither spots nor aurorae (this also applies to Hayakawa et al. 2017c). The alleged aurorae in Hayakawa et al. (2015) and Kawamura et al. (2016) show a broad peak around full moon, not expected for aurorae. Hayakawa et al. (2017a) use the Korean report At night, the gate of heaven was opened (between AD 992 Dec 26 and 993 Jan 25, i.e. close to the 14 C variation AD 993/4) to estimate the Dst index of solar activity, even though the text does not fulfil any discriminative aurora criteria (except night-time). Most of the above publications include very few Chinese texts and translations, and their tables with abbreviated keywords do not allow the reader to consider alternative interpretations (the tables also do not specify which records mention night-time). We have compared some of their event tables with previously published catalogues and found various discrepancies. There are also intrinsic inconsistencies, misleading information (lunar phase for day-time events), and dating errors. We present Chinese texts and translations for some of their presumable new aurorae: only one can be considered a likely true aurora (AD 604 Jan); some others were selected on the sole basis of the use of the word light or rainbow. Several alleged new aurorae present observations beside the Sun during day-time. There are well-known comets among their presumable aurorae. We also discuss, (i) whether heiqi ri pang can stand for black spot(s) on one side of or beside the sun, (ii) aurora color confusion in Hayakawa et al. (2015Hayakawa et al. ( , 2016, and (iii) whether white and unusual rainbows can be aurorae.