Hayadi's Comet

Hayadi's Comet, also known as Comet Hayadi and officially named 1813P/Hayadi, is a short-period comet visible from Zamin and Yatim every 30 to 35 years. Hayadi is the only known short-period comet that is regularly visible by the naked eye and also the only one that appears up to three times in a human's life by modern lifespan standards, being widely documented throughout history. It last appeared in early 2023 and will appear again in early 2058.

Hayadi's periodic return has been observed by astronomers since at least prehistory, the oldest record known in 42 BC, but it wasn't until 1813 that the Alarian mathematician and astronomer Tamir Hayadi understood that these visits were re-appearances of the same comet, and predicted its orbit. As a result of this, the comet is named after him, and the official name takes reference from the year he made the predictions.

The first detailed view of Hayadi's Comet with spacecraft was in 1988, providing detailed information about its size, the composition of its nucleus, and its coma and tail mechanism of formation. These observations confirmed other predictions made by Hayadi himself as well as his colleague Gürsel Adelbert, who proposed that it was composed of a mix of volatile ices —such as water, carbon dioxide and ammonia— and dust, giving it its characteristic blue-white colour.

Study of the comet
Hayadi's Comet was the first to be recognised as a periodic comet and the first one to have its orbit accurately predicted by Tamir Hayadi in 1813. It was observed in detail in the past in Ostrovia in 1673 by the Coutestahnian astronomer Anselmo Edoardo Aubin. The data providen by Aubin shows that the earliest depictions of Hayadi's were in 42 BC, but he never explicitly mentioned that the comet he observed was the same as the one observed in the past.

In his observations, Hayadi observed that the characteristics of Aubin's comet matched those of the comet observed in 42 BC, as well as the one observed in posterior years, such as the Great Fireball of 1113, the 1428 observations by Tomislav Aymeric and the 1568 observations by Diomidis Basilio. He proved that all of them corresponded with the same celestial object, that returned every 30 to 35 years. With that, he made a prediction of the next return of the comet, early 1848. That prediction didn't end up being fully correct, as Hayadi's returned on the Christmas of 1848. This late appearance is nowadays believed that it was due to the fact that Irhan's gravity slightly perturbed Hayadi's orbit. Nonetheless, Hayadi never saw if his prediction was right or wrong, as he died prematurely two years before in a railroad accident.

In 1988 various spacecreafts visited the comet, including Outbounds 1 and Outbounds 2, OSES and Brave New Worlds. Thanks to them nowadays detailed information of the comet is known.

Sightings
Hayadi's calculations allowed us to find the sightings of the comet in the historical record. The following table shows every recorded sighting from 42 BC onwards. The astronomical designations are the following: 1813P is the name of the comet, then afterwards comes year when it happened, and I to III indicates for how many months was it seen afterwards. For example, the 2023 sighting would be classified as 1813P/2023II.