A medieval poet and some buried trees have just revealed something very strange to us about the 13th century Sun

At the beginning of the 13th century, the Sun was passing through a solar cycle much shorter than those that exist today, but extremely intense. Having such specific details is complicated for such a distant time, when scientists did not have instruments to measure this type of activity. However, there is something that today’s scientists do have and that has helped them detect this event: a book of poetry and many trees.

Art and science. A team of scientists from Okinawa Institute of Science and Technology has described this event using two types of data. On the one hand, a poem written in 1204 by the Japanese writer Fujiwara no Teika. On the other hand, the observation of the rings of buried tree trunks in northern Japan. The conclusion is clear. While today solar cycles are usually around 11 years, back then there were some 6 or 7 years, but the activity was high enough to lead to the formation of auroras in Japan.

A proton explosion. When solar activity is very intense, phenomena such as solar flares or the coronal mass ejections. The first is a sudden release of electromagnetic radiation from the solar surface, while the second consists of the expulsion of matter, normally charged plasma particles, from the Sun’s corona. Associated with these phenomena, proton explosions occur, in which these charged particles move at high speed.

rare isotopes. Normally, a good part of these charged particles and cosmic rays fail to pass through the Earth’s magnetic field. However, when they are very intense they can reach our atmosphere in greater quantities and interact with the gases in it. In this reaction, isotopes such as beryllium-10 or carbon-14 can be formed. These are beryllium or carbon atoms with a different number of neutrons in their nuclei than the beryllium and carbon that are most abundant on Earth. Knowing this process is useful, because it can give us clues on two levels.

On the one hand, beryllium-10 is deposited in ice sheets, while carbon-14 It oxidizes, transforming into carbon dioxide and becoming part of the carbon cycle. In this cycle, living beings incorporate it into their cells in different ways. For example, plants do this through photosynthesis. And this is where what has been so useful to these scientists begins.

Solar dating and meteorology. Carbon-14 is often used to date fossils, since they come from living beings that once incorporated that isotope into their tissues. The moment a living being dies it stops incorporating carbon-14. From that moment on, it begins to disintegrate at a known rate, so it can be estimated approximately when it died. The point is that, beyond that, if carbon-14 levels are unusually high, it can also be determined if there was an extreme solar event.

The poem describes a dawn

The poem. in his diary Meigetsukithe poet Fujiwara no Teika described the observation of “red lights in the sky over northern Kyoto.” This city is at a latitude too far south for auroras to form, but that is clearly what it describes.

The auroras They are the result of a type of interaction between the gases in the atmosphere and the charged particles of the Sun that causes the emission of visible light. They are normally formed at the poles, as they are the points on the Earth where the magnetic field is most vertical, so that it acts as a funnel, so that these particles can pass through it. When they occur far from the poles it is because solar activity has been very intense and the resistance normally opposed by the magnetic field has been exceeded.

What the trees tell. The rings of tree trunks are a kind of natural calendar. They are formed from the inside out, so we can count them and calculate how the years have passed. For this reason, the authors of the study that has just been published They wanted to analyze the equivalent buried tree rings at the beginning of the 13th century. In the rings from the period from winter 1200 to spring 1201 they found an increase in carbon-14 levels. This also agrees with the levels of beryllium-10 found in ice deposits from that same period. Everything agrees.

Also in China. There are historical records from the time when Chinese astronomers also described red lights in the sky. Therefore, it seems clear that there were auroras at unusual latitudes.

A very rare case. The most curious thing about all this is that this phenomenon did not occur at the peak of the solar cycle. It possibly took place around its periodic minimum. If there was less activity, why so much aurora and carbon-14? This is something that, at the moment, scientists have not been able to explain. Perhaps there were also many auroras at the peak, but no poet stopped to write about them. Tree rings would have to be analyzed to see what carbon-14 tells us. What is clear is that the Sun was burning in those medieval times.

Image | Masaaki Komori (Unsplash)/Wikimedia Commons | Kush Dwivedi (Unsplash)

In Xataka | A sunspot 17 times larger than Earth caused red auroras across half the world. It is a very rare event