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What are Comets?

Geography | 8-12 yrs | Animation, Video

Comets are small celestial bodies. Scientists cannot seem to agree on whether comets are dirty snowballs or snowy dirtballs because of the mixture of ice, gas and dust that they comprise. They are different from asteroids because they are huge balls of ice and gas. Comets are said to originate from the Oort cloud, a group of icy bodies in the outer solar system. They have remained largely unchanged since they formed, which is why scientists are very fascinated with them and the ancient material they carry.

Unlike meteoroids and asteroids, comets have been known to humanity since we were able to record our past- probably because of their distinct shape and tail and the fact that they would appear from nowhere and disappear just as mysteriously. Early sightings of comets have been recorded in various cultures around the world and were considered bad omens- such as the death of nobility, famine or even attacks from the heavenly realm.



The solid ball of the comet is known as the nucleus or core. It mostly consists of ice, dust and dark organic matter with the ice comprising mostly of frozen water. The frozen material can also be methane, ammonia or carbon dioxide.


When a comet nears the sun, the frozen parts of the comet begin to turn to gas. The gas forms a cloud around the nucleus that is known as a coma. Often this cloud is filled with hydrogen and is then referred to as the hydrogen cloud.

Dust tail

Radiation from the sun also charges the dust particles of the comet causing it to get scattered over up to 10 million km. This dust tail is the most prominent part of the comet seen to the naked eye.


Comets can take anywhere from several decades to a few hundred years to complete one orbit around the sun. When it is closest to the sun it is known as a perihelion and the opposite is called an aphelion. Since the earth is relatively close to the sun we see it during its perihelion. Many comets have been sighted and recorded throughout history. Here are some of the more

famous ones-

Halley’s comet- It was last seen in 1986. Its orbit takes 75 years, which means it will next be seen on earth in 2061.

Comet Hale-Bopp – was sighted in 1995. Scientists believed that it would disintegrate during its perihelion, but it survived and should come back around the year 4385.

Comet Lovejoy – is the most recently discovered comet. It was first sighted by Trey Lovejoy in Australia on November 27th 2011.

No matter what the direction of the comet, its tail will always point away from the sun. Can you find out what makes this happen?

Zipping muddy snowballs

For more interesting Geography articles and videos, visit: http://mocomi.com/learn/geography/