What is a planet?

If you know what a planet, then you know more than scientists and astronomers.Because they do not believe in the definition of the term.For example, some people consider Pluto a planet, the other - no.

originally so named Mars, Venus, Jupiter, Saturn, Mercury.Incidentally, the names of the planets came to us from Greek and Roman mythology.The land was for the ancient special, different from other celestial objects.Moon and Sun too, as members of the "wandering bodies" a slightly different nature.Have you ever wondered why we have one day off in seven days?This is not reflected in the Russian language.But the French, Italian, for example, it is clear correlation between this "The Magnificent Seven" and days of the week: Monday - the moon, Tuesday - Mars, Wednesday - Mercury, Thursday - Jupiter, Friday - Venus Saturday - Saturn, Sunday - Sun.

Uranus was discovered in the 18th century.Then, thanks to research Verrier and Adams, Neptune (the 19th century).In 1930, the world learned of the existence of Pluto.This discovery did Clyde Tombaugh.Pluto is still known as the ninth planet.Is it so?In order to answer this question, we need to understand what planet?

itself is a concept we have formed historically.In the sky, we see five planets with the naked eye.And it turned out to be much more difficult, if asteroids were brighter.Astronomers have agreed to call the object a planet that is orbiting stars besides it must be large enough to become a sphere of gravity.Many comets and asteroids is very strange forms.

exact definition of "what planet" was not.Yet beyond Pluto is the name stuck.In fact, this is a very strange object, and it is very different from the other major planets.The orbit of its somewhat more elongated.As it turned out, Pluto is very small.Much less than astronomers previously thought.All the planets of the solar system are located "growth": 4 terrestrial in the beginning, then the giant planets.Pluto here clearly does not fit.

then discovered Pluto - Charon, which is almost the same size.It is also somewhat atypical: all the planets satellite is much smaller.

Kuiper (American astronomer) has suggested that beyond Neptune is the asteroid belt.It was another blow to the "status" of Pluto.Such times are really there!Currently, he is known as the Kuiper Belt.The bodies in it are somewhat different from asteroids.They are very much similar to Pluto, only smaller in size.Now it became clear that Pluto - one of the largest Kuiper belt objects.But while the former name for it persists.Scientists have for the most part, people are conservative, so have decided to leave everything as it is.

And yet, what planet?In the near future this issue will be very important.Since it is known that the already open planet other stars.

main parameter - the mass.Smaller objects - asteroids more massive - star.With all the stars clearly.They must have a high temperature to the thermonuclear processes.The planet in its orbit to be one, if a lot of objects ("belt"), this asteroid.