1408 celestial mystery solved: Scientists reveal identity of 'Zhou Bo star' that disappeared after 10 days

Chinese astronomers saw a strange object shining brightly in the sky in October 1408. This was during the Ming Dynasty, when a stationary yellow object remained visible for over ten days. It was an oddity, as no one had ever seen something like it. Officials were so intrigued by it that they made a record of it.

It has been known as the “guest star”, a mysterious cosmic object. Scientists have been peering over historical astronomical records for years to understand more about the object. Now they have finally confirmed what it was, thanks to a recently unearthed report by a court official.

The details have been posted to the preprint server arXiv by researchers led by Boshun Yang, an astronomer at the University of Science and Technology of China.

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Guest star, “as large as a cup”, “yellow and smooth”

He cites a report by Hu Guang, a court official in the Ming Dynasty, who wrote about the guest star only weeks after it was seen. His details have helped cover a large gap in information, since earlier records lacked crucial details.

According to the study, Hu wrote a memorial that was in possession of the Imperial Astronomical Bureau. The text describes the object "as large as a cup, with pure yellow colour, smooth and bright". It remained "stationary and calm over ten days of measurement and observation" in the southern region of Niandao.

New record proves the 1408 object was real

The discovery of this record by Hu proves that the star did appear in the sky and was not a misinterpretation caused by translation. Second, it shows how court officials, while reporting to the king, were expected to use positive words instead of stark warnings that might be perceived as negative. Words like "smooth and bright" were used instead of "spikes" or "rays."

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Not a comet, not a meteor, but a nova

Researchers deduced that since the object remained in one place for 10 days, it was not a comet or meteor, but a star, more precisely, a nova. That meant a star had undergone a violent death and flared up, becoming visible to humans on Earth. It had a stable light curve, which suggests that it was a specific type of nova with "plateau" characteristics, which meant the light stayed stable for a long time.

The nova was extremely bright, as proven by the use of the term "Zhou Bo star," which was only used to refer to extraordinarily bright phenomena. Besides, it had to be something so important that it warranted documentation by Chinese court astronomers. All these observations led Yang and his team to believe that it was a major nova.