The chronology of lunar eclipses during the High Medieval Period (1100–1300): A determination of atmospheric aerosol abundances and a quantitative wood anatomy
During a total lunar eclipse, the Moon is fully in Earth’s shadow. A dark Moon indicates that volcanic aerosols are highly abundant in the stratosphere, whereas a reddish Moon suggests that they are scarce (Fig. 1). Guillet et al. examined historical accounts of lunar eclipses from the High Medieval Period (1100–1300), and estimated the abundance of volcanic aerosols from the descriptions of the colour and luminosity of the Moon. They used this information to refine the timing of a cluster of volcanic eruptions that occurred during this period, and which had previously been identified using ice-core measurements4. The authors found that seven of these eruptions generated aerosols that could have had a role in the transition from the Medieval Climate Anomaly (around 850–1250) to the Little Ice Age (around 1300–1850).
Most of the refracted sunlight that illuminates the eclipsed Moon passes between 5 and 25 km above the surface of the Earth19. The residence time of upper tropospheric aerosols is on the order of a few weeks. Dark lunar eclipses are more likely to show high cloudiness in the sky after large volcanic events. We thus assume that lunar eclipses of reddish or coppery colour (that is, with an L value >1) observed in the aftermath of HMP eruptions indicate that aerosol veils were mainly confined to the troposphere and probably had limited climatic impacts. The robustness of our approach was assessed by comparing our results with sulfur isotope records (Δ33S) from Dome C (Antarctica)3, which have proven a valuable proxy to distinguish between eruptions whose plumes reached the stratosphere at or above the ozone layer and those that remained below3,102,103,104,105,106,107.
A quantitative wood anatomy. Edwards et al.100,101 attempted to narrow the period of peak cooling associated with the Laki eruption to late summer 1783 ce using cellular-scale tree-ring proxy measurements. These findings contrast with MXD reconstructions that suggest that the entire 1783 ce summer was exceptionally cold and with tree RW reconstructions that mute the cooling. QWA data is more precise and can identify peak cooling following volcanic eruptions, compared to treeWr and MXD. Estimates of eruption timing may be further refined with the QWA analyses included in this study. Despite promising results, highly resolved QWA is at its early stage. Due to cost and labour intensive, it is not likely that an operational network of QWA records will be available soon.
Calculating lunar eclipses using the Danjon scale: results from John’s work at Worcester Cathedral in 1287 on a case of an eclipse
The resulting struggles are clear in the writings of a monk known as John, who chronicled sunspots and a solar eclipse from his post at Worcester Cathedral in England at the start of the High Medieval Period. John didn’t know how to calculate the lunar eclipses because he didn’t understand the Islamic methods. The planetary tables were valued, and they formed the basis of textbooks on astronomy. Johannes de Sacrobosco’s book was written in around 1220 and it quickly became a popular book. How, then, could there be continuing doubts about the timing and identification of lunar eclipses?
The Latin translations of Islamic texts made their way to Europe in 1170. However, these texts used an entirely different calendar and referenced dates that were meaningful only for their original compilers. They described the astronomy that was done far away from northern Europe. Early translations were literal and offered little help to users unfamiliar with the Islamic calendar.
The solar year didn’t align with the years in the Julian calendar. It was argued by Sacrobosco that the error had reached a certain point and that Easter was actually being celebrated on the wrong day. Church leaders were concerned that changing the calendar would be difficult. The timing of phases of the Moon was therefore out of step with the calendars of major religious institutions.
This scale was designed specifically to estimate the brightness of the Moon with the naked eye, which is well suited for our purpose because no high-resolution, technical aids existed in the twelfth and thirteenth centuries. The descriptions of lunar eclipses were assessed using a scale called the Danjon scale. Note that accounts referring to penumbral and partial eclipses were excluded from analysis as only total lunar eclipse observations are suited to this method16,17. The most common adjectives describing lunar eclipses in medieval texts are ‘rubeus-a-um’ and ‘sanguineus-a-um’, meaning ‘red’ and ‘blood-coloured’, respectively; lunar eclipses so described were rated L = 3. A Danjon scale value L = 4 was attributed only if the eclipsed Moon was described as exhibiting intense and various colours, such as in this example by the English monk Bartholomew de Cotton of an eclipse on 22 October 1287 ce: “Eodem anno luno in plenilunio visa est crocei, rubei ac varii colori” (“The same year, during the full Moon, the Moon exhibited yellow, red and many other colours”). If the author specifically noted that the Moon had become invisible during the eclipse, a Danjon value of 0 was attributed.
During a total lunar eclipse, the moon is partially illuminated by light while it passes through the shadow of the Earth. The sunlight spectrum is affected by scattering and absorption. At the shortest wavelength, ryasp scattering is more effective than orange or red-coloured light. When the stratosphere is little perturbed, the eclipsed Moon thus tends to appear copper to deep red. The effect of a turbid stratosphere is amplified the scattering of visible light, diminishing transmission through the atmospheric limb which reduces the effect of the Moon in eclipse. It can appear to be completely gone in extreme cases. The colour and luminosity of the moon were rated on a scale of 0 to 4, with 0 meaning zero and 4 meaning four.
To determine the period (Tdark) when SAOD exceeded 0.1, that is, conditions for a dark total lunar eclipse (step 2.1), we used four (five for Samalas) SAOD time series. The SAOD time series around ce Krakatau and 1991 Ce Pinatubo eruptions can be found in the data. Satellite observations and ground based optical and volcanic evidence make up this dataset, which has been reported since 1850. We also extracted SAOD time series for the Pinatubo eruption from the Global Space-based Stratospheric Aerosol Climatology (GloSSAC v2) dataset38, which spans the period 1979–2018 ce. As observational data are unavailable before the mid-nineteenth century, we estimated the residence time of volcanic stratospheric aerosols for each eruption (UE1–UE6) from the eVolv2k database4. In the case of the 1257 ce Samalas eruptions, we also relied on results of the IPSL climate model (IPSL-CM5A-LR)40, as it treats aerosol microphysics and has been validated for the well-observed case of the 1991 ce Pinatubo eruption58.
There are some limitations to the procedure presented in this study to constrain HMP eruptions. The following sections address some of the questions and give several avenues of research to further refine our estimates.
It is necessary to observe totality during good weather conditions, that is, clear, dark sky, not too close to the horizon and not close to dawn or dusk.
The Early Night of the Little Ice Age: Observations in 1300-1300 ABBA and Supplementary Dataset S1 (Midnight of the Rat)
The reports should have contemporary information and should be told by an person who witnessed it. These conditions are not always met for the medieval sources available (see Supplementary Dataset S1 for more information).
It’s clear in the morning. After the hour of the Snake [9 am–11 am], heavy rain and flooding. People died when houses were swept away. At the hour of the Horse [11 am–1 pm] the weather began to clear. The Moon was not seen correctly during the hour of the Rat.
The development of the Little Ice Age, which was one of the most frigid periods in recorded history, could be key to the understanding of the climate in 1100–1300.
The authors identified nearly 400 accounts documenting a total of 119 lunar eclipses. The moon coloration and darkness trait can be used to determine how much of a volcanic haze was present at the time.
Medieval Solar Particles as a Backstop for Planet Cooling and Atmosphere Rejuvenation after the Runaway Global Warming
Knowing a little more about what happened in the past can clarify some aspects of the proposal to use solar particles to reflect sunlight back into space. Some scientist argue that such efforts could serve as an emergency backstop to cool the planet and avert the worst effects of runaway global warming.
The study is a nod to the Medieval observers who have used historical records to record social and political trends. If they can provide an accurate record about social and political events, why not give the same information about natural events?