Planets and Dwarf Planets:
Ancient greek named some celestial bodies planḗtai (English = Planets) because it mean wanderer in greek. In the 19th century, people identified 15 planets in our solar system, though in the 20th century people didn't consider some planets, actual planets, and so not part of our solar system. They only considered 10 planets, real planets.
Criteria that had to be met to classify a planet, and actual planet, was that they needed to orbit the sun, they needed to be a nearly-round shape, and they had to be able to clear other objects in it's neighbourhood. Criteria that had to be met to classify a planet as a dwarf planet, was that it also had to orbit the sun and be nearly-round shaped, but it should not be able to clear other objects in it's neighbourhood and it isn't a moon.
Scientists think that a planet should be classified by what it is near, and not by it's properties. I think it is important to be open to all possibilities, because science advances and changes every day. It is important to be flexible and accept that. Just like in the 19th century, when people thought they knew what a planet was, their findings changed in the 20th century.
The world is something still to be discovered.
PlanetQuest Historic Timeline:
I think that the advancement of all the technology involved in science has been the main part in the finding of new things. In the beginning of the video, people were just looking at the sky, and trying to figure out things by just that, and then over the course of time people started to invent new technology and that help them know more about all the planets. I found the names of the planets very interesting, since some of them are things like B3458-1b. I find that a little bit confusing. I wonder how the technology will evolve in 20 years: will it make things easier, or will there be advancements that won't have a big effect on our planet?