Solar System?

Question

What exactly has happened with Pluto not being part of the 9 planets, and the real meaning of what's behind the "Milky Way"

Answer 1

Pluto was demoted from planet status by the International Astronomical Union because more and more bodies were being discovered in the far reaches of the solar system which were similar in size the Pluto, had very similar orbits, and two (Eris and 2003EL61) even had moons.
Pluto's planetary status had already been in question for many years due to the fact that a) its orbit is so eccentric it appears to have been jettisoned from an orbit with Neptune, b) its moon Charon is almost as large at is is, and c) there were seven moons (Ganymede, Titan, Callisto, Io, the Moon, Europa, and Triton) which were larger than this smallest planet.
As more trans-Neptunian objects were being discovered, the question became "just what makes a planet?" At one point, as many as 30 new planets were being proposed! The deffinition that the IAU finally settled upon was this:
1) It is in orbit of the Sun
2) It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape (in other words, it's round)
3) It has cleared the neighbourhood around its orbit.
The third criterion knocked Pluto out of the planet category since there were a number of smaller bodies called Plutinos which shared (roughly) an orbit with the former planet.

The Milky Way? I assume you mean the name. It refers to what appears to be a band of white light illuminating the sky in what seems to be a rough line across the sky resembling a kind of street. Go to a rural area around May or June and look up at the sky -- you'll be able to see it clearly and see exactly what the name implies.

Answer 2

The International Astronomical Union started the whole thing, when another body was found beyond Pluto that was 5% larger but was considered a Kuiper Belt Object (not a planet). If size was the criteria for planethood, then Eris should also be called a planet.
Basically the Union voted on a firm definition of planet, and poor Pluto just didn't make the cut, so it has been demoted to "dwarf planet", along with the new body Eris and the asteroid Ceres.

Not sure what you mean by "the real meaning of what's behind the Milky Way".
The Milky Way is just one galaxy in a universe of billions of galaxies. We consider it important because it happens to be the one our sun is part of, no other reason.

Answer 3

They were finding so many space rocks out there, they had to come up with more solid definitions. They gave a size factor and Pluto was too small. I think it's not round also. It's still out there though.

Answer 4

1. pluto is too small can be categorized as a planet
2. when pluto categorized as a planet, it was just because of the letters of kids that asked pluto to be a planet..
3. pluto has a different orbit with the others, and also its orbit through the orbit of neptune.

milky way is named that because it spreads out like milk in a glass that you stir it with spoon. circular view with the center point.