Jongjin Park
In pure Korean, a comet is called a tail star because it means a star with a tail, or a star star because it flies like an arrow. Humanity thought the universe was orderly. The sun and moon moved repeatedly, the stars in the night sky found their original positions every time the four seasons changed, and comets suddenly appeared and disappeared, so they were considered ominous celestial bodies regardless of the East or West.
Meanwhile, as astronomy developed and observational data accumulated, it was thought that there might be some rules to the activity of comets. Edmund Halley of England was the first to notice that there was a period in the movement of a comet, and after calculations, he calculated whether the comet would approach the Earth again. The time was expected, but Halley died before then. Exactly after his death, around 1758, the comet appeared, and later generations named the comet the astronomer’s name in honor of his achievements. This is the famous Halley’s Comet.
A cloud called a coma surrounds the comet, which is a phenomenon that occurs when the comet’s nucleus vaporizes as it approaches the sun. The coma is made up of cosmic dust and ice fragments, small pieces of which are blown by the solar wind and appear like comet tails.
The size of a typical comet is less than 30 km in diameter, but as it approaches the sun, its tail gets longer, sometimes being as long as four times the distance between the sun and the Earth. A comet has two tails. When an icy comet approaches the inner solar system, the heat from the sun vaporizes volatile substances on the surface and surrounds the comet with surrounding dust, which is called a coma. However, the coma is pushed behind the comet by the solar wind, forming a tail made of dust, and the other tail formed next to it is ionized gas that emits light.
Looking at the structure of the solar system, there are a total of eight planets orbiting around the sun, and outside of it there is a group of asteroids called the Kuiper Belt, and far beyond that, there is the Oort Cloud Belt, where it takes about a year for light to leave the sun’s surface to arrive. Asteroids spread across the Kuiper Belt sometimes turn toward the Sun due to the gravitational pull of Jupiter, Uranus, or Neptune, and these become comets. Comets with a period of less than 200 years are called short-period comets, and those with longer periods are called long-period comets. The period of Halley’s Comet mentioned earlier is 75 to 76 years, so it is a short-period comet.
Comets originating from the Kuiper Belt are short-period comets, but comets originating from the distant Oort Cloud are classified as long-period comets. There are only a few long-period comets known so far, but among them, Comet West has an orbital period of over 500,000 years. .
A comet is a completely different celestial body from a meteor called a shooting star, but if a piece of the tail left behind by a comet accidentally overlaps the Earth’s orbit, when the Earth passes through this area, the comet’s spill is pulled in by the Earth’s gravity and oxidizes in the atmosphere. The phenomenon is a meteor shower.
It was assumed that the water existing on Earth came from the large amount of ice contained in comets, but because the ratio of isotopes, including deuterium, in seawater is different from that of comets and rather matches that of asteroids, the theory of the origin of water from asteroids is now more likely. (author)
Jongjin Park
