A dodgy sky

A regular, periodic and predictable cosmos: this was the starry sky to the ancients. So reliable that they used it to measure time and to orient themselves in space, to decide the seeding and prepare for the harvest. So far and cosy to host myths and gods.

Any unexpected change, like a comet or an eclipse, was a sign to be interpreted or a message to be decoded - sometimes positive, but more often a negative one, depending on the culture and people watching it: a symbol of an obscure power expressing its will, hidden beyond the heavens.

And how to interpret a new shining star that was born in the firmament, that was visible in the sky for months and then slipped back into the darkness? If stars come into the world and then fade away under our mortal eyes, what reliability can the cosmos have? For Christian Europeans, this phenomenon was even more incomprehensible: the cosmos was a direct emanation  of God, eternal and unchanging. A new star was simply impossible.

However today we know that some phenomena such as Galactic supernovae, that are stellar explosions occurring in our Galaxy, can be seen with naked-eye.

According to historical sources, only nine records of new stars over the past two thousand years are attributable to supernovae. The recordings are mainly due to Chinese astronomers. Their stellar remnants have been identified only for the five most recent records (1604, 1572, 1181, 1054 and 1006 AD). For the four oldest ones (393, 386, 369, 185 AD), the sources are historical accounts or chronicles distant in time from the narrated events.

Camille Flammarion - 1881 - Tyco Brahe Observing SN1572

 

As far as we know, two supernovae had a decisive influence on the history of thought and, ultimately, on modern science: the supernova observed in 1572 by Tycho Brahe, when Galileo was only 8 years old, and the one known as Kepler's supernova that appeared in 1604. At that time, Galileo was 40 years old and he had reached his full scientific maturity. He taught astronomy at Padua in the Republic of Venice. When he learned of  the "nova", he made three public speeches - today we would say public conferences or cafes scientifiques - in which he expressed his position in favor of Copernicanism. He did not publish anything. Just four years earlier, the Italian philosopher Giordano Bruno was burned at the stake in Rome for his heretical ideas. And a new star born in a kingdom of heavens made by incorruptible matter was indeed a dangerous idea. Dangerous, but more and more lively.

After 5 years of studies, Galileo pointed the telescope towards the sky, observing  Jupiter’s moons and published his observations in Sidereus Nuncius. Later on, he also observed the sunspots. More sky variability, more imperfections.

The path connecting the kingdom of heavens to the sub-lunar region, now considered of the same nature, was eventually and dramatically drawn.

Appendix 1

Historical supernovae candidates

 

Date of discovery

Visibility

China

Japan

Korea

Arabia

Europe

AD1604

12

few

 

many

 

many

AD1572

18

few

 

two

 

many

AD1181

6

few

few

 

 

 

AD1054

21

many

few

 

1

 

AD1006

36

many

many

 

few

two

AD393

8

one

 

 

 

 

AD386?

3

one

 

 

 

 

AD369?

5

one

 

 

 

 

AD185

8 or 20

one

 

 

 

 

 

Column 1: year of identification; column 2: visibility period (in months); columns 3-7: geographical area and number of historical records.

 

Further readings:

The Historical Supernovae


D. A. Green, F. R. Stephenson, "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture Notes in Physics, Springer-Verlag, Berlin-Heidelberg-New York

Ice Core Records – From Volcanoes to Supernovas - Summarizing the Evidence for Dating the Cassiopeia A Supernova Event