Distinguishing between meteoroids, meteors, meteorites and comets can be a challenge even for those interested in astronomy. The differences are rather elementary, however, once one understands the definitions. The following guide can help you understand these astronomical terms.
Meteoroids, meteors, meteorites are terms that are closely related to each other, while comets are quite different. A meteoroid is a solid object that transcends through space. It’s size has been described as ranging from larger than an atom to smaller than an asteroid. Beech and Steel tried to quantify its size by saying that it is 100 µm and 10 m across. Micrometeoroids is the term given to those that are too small to be considered meteoroids. The material of which they are made ranges, consisting at times of dense rocks full of nickel to metal to other objects. There are a great many meteoroids, with different orbits and speeds.
A meteor occurs when there is a visible path, which has entered the Earth’s atmosphere or that of another planetary body. Thus if you look in the sky, what you see is the meteor. The mesosphere is where most occur, in a typical 75km to 100km altitude.
They may appear very bright, and you may have visions of this gigantic rock going across the atmosphere. In truth, many are the size of a simple pebble. They come very often, and may occur in “meteor showers.”
If the meteor does not disintegrate as the vast majority do, then it can hit the Earth or another planet. When it does, then the term meteorite applies.
Comets are very different from the meteoroids, meteors, meteorites, which as previously described are all terms for the same object under different conditions. Comets are icy. Proximity to the sun causes them to possess a coma, which is defined as a thin and non-permanent atmosphere. Oftentimes they have a tail, producing the stereotypical image of a comet. Solar radiation and wind precipitates this thus it can lengthen as it nears the sun. Ice, dust and small rocks can be contained in the comet nuclei.
There are almost 4000 known comets, however many more likely exist. Their orbits around the sun vary greatly. They can be seen at different times, some of them with a range of a few years and others with a thousand times that.
Meteoroids, meteors, meteorites and comets are some of the most common terms one will hear when learning about astronomy. The above tips can help you understand the differences in these celestial bodies.
Sources:
http://www.brighthub.com/science/space/articles/66254.aspx
http://en.wikipedia.org/wiki/Meteoroid
http://en.wikipedia.org/wiki/Comet
