Astronomy enthusiasts should all know.

The so-called supernova explosion.

Refers to a kind of violent explosion certain stars undergo when they approach the end of their evolution.

Such explosions are extremely bright, and the sudden electromagnetic radiation during the process often illuminates the entire galaxy it resides in.

It can last for weeks to months before gradually fading into invisibility.

During this period.

A supernova radiates an amount of energy comparable to the total energy radiated by the Sun throughout its entire life.

On the other hand.

While supernova explosions in the universe are a dazzling phenomenon, magnificent, and enchanting.

For humanity, it actually poses a certain risk.

During the explosion, a supernova releases a large amount of gamma rays, which radiate at light speed to the Earth's atmosphere.

Gamma rays induce a special chemical reaction when they interact with the atmosphere:

They convert nitrogen molecules into nitrogen oxides.

This consumes the protective shield for life on Earth, which is the ozone layer.

Leading to Earth's life being directly exposed to harmful radiation like solar winds and cosmic rays.

For example, there have been five mass extinction events in Earth's life history, and the second ranked is the Ordovician mass extinction.

The Ordovician mass extinction occurred 440 million years ago, resulting in 85% of Earth's species becoming extinct and later triggering an ice age.

In 2005.

NASA and the University of Kansas jointly released a research report.

The report suggested that this mass extinction event was likely caused by a gamma-ray burst from an extreme supernova.

Based on model reconstructions of the event.

The entire process might have lasted just ten seconds, yet it destroyed half of Earth's ozone layer.

Ultimately causing ultraviolet rays from the Sun to bombard Earth, leading to massive death on the surface and causing biological extinction. (doi.org/10.1099/ijs.0.02503-0)

By the way.

Currently, the most discussed topic in the astronomy community is Betelgeuse; recently, its photometric data has been somewhat abnormal, possibly indicating a supernova explosion.

However, due to its distance, this occurrence wouldn't have much impact on Earth's organisms.

After all, radiation should comply with basic ... basic principles of physics.

Besides Betelgeuse,

another star that might undergo a supernova is WR102 in Sagittarius.

It's a rare oxygen-rich Wolf-Rayet star, and based on existing models, this star has likely already exploded.

Judging by its distance.

If you can live another 1500-2000 years, you should be able to witness this spectacle, not too difficult.....

In summary.

Over the past two thousand years, humans have observed a total of eight supernova explosions.

Among them, many are impressive:

For instance, the earliest recorded supernova was SN185, seen by local astronomers in 185 AD.

Also, the brightest recorded supernova is SN1006.

Supernovae SN1572 and SN1604 were the last two supernovae in the Milky Way observed with the naked eye, which significantly impacted the development of astronomy in Europe.

They were used to refute Aristotle's fixed universe theory beyond the Moon and planets, marking a landmark discovery.

With the advent of the telescope era.

Humans subsequently observed SN1885A, SN1987A, and SN2006gy.

Of course.

Upon reading this far.

Students who didn't fail mathematics might have noticed a question:

Despite having eight supernova explosions, why were only seven mentioned above?

That's right.

The remaining supernova explosion was the Crab Nebula supernova of 1054 AD that Old Su personally experienced.

Simultaneously.

It was the most widely observed supernova explosion in human history.

Its distance from Earth is about 6500 light years, meaning what we see now is a scene that occurred 6500 years ago.

Analyzing historical records indicates.

The supernova explosion that created the Crab Nebula happened in April or early May, and by July, when brightest, it had an apparent magnitude between -7 and -4.5.

During that time, it was brighter than any celestial body in the night sky except for the Moon.

This spectacle even lasted until the 21st century in later generations:

At that time, the Crab Nebula still possessed numerous elliptical filamentary structures surrounding its diffused blue core region in the visible light zone.

Spanning 6 arcminutes in length and 4 arcminutes in width.

It is one of the celestial bodies with the largest apparent diameters.

Of course.

Also one of the most beautiful celestial bodies. (Interested individuals can search for it, it's really stunning, and visitors to Shanghai can spend 60 to buy an astronomy museum ticket, definitely worth it)

However, compared to the first observation of the Moon, Xu Yun did not personally get involved this time.

Instead, he let Old Su try it himself.

As the saying goes.

Teaching someone how to fish is better than giving them fish; if you only impart knowledge blindly, everything will revert to its original state once you leave.

"Yes, yes, rotate the Star-finding Mirror first, wait, it's gone too far."

"Move the cross-wires a bit closer....."

Seeing Old Su humming and fiddling with the equipment, Xu Yun appeared very patient.

Compared to those rarely-read Readers from the past life, Old Su was practically a model student.

After a while.

Seeing that Old Su had adjusted it almost correctly, Xu Yun asked:

"Old Sir, do you recognize the position of Bi Su?"

Old Su quickly nodded without much hesitation and said:

"Bi Su, one of the 28 lodges, the fifth lodge of the Western White Tiger.

In the star chart authored by this old man, the position of this star is marked."

Bi Su, also known as Bi Yue Wu.

It is composed of eight stars and is one of the ancient star officials in Huaxia.

The origin of Bi Su is quite simple:

Its eight stars combined resemble the shape of the Chinese character '丫', which the ancients thought looked similar to a long-handled tool used for capturing small animals, called 'Bi'.

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