| We all grew up learning in school that we
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| | 2) Size was the second factor. Remember
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| have 9 planets in our solar system. And
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| | that Pluto is actually smaller than our
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| the most popular and mysterious of them
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| | moon. But who is to say exactly how big a
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| is Pluto. No one loves the planet Pluto
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| | planet needs to be? Well, the astronomers
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| more than kids! In fact, after Pluto was
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| | decided that to be a planet, the object
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| discovered in 1930, the name was
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| | has to be big enough that gravity
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| suggested by an 11 year old schoolgirl
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| | squeezes it into a round shape (a sphere)
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| living in Oxford England who was very
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| | like an orange or a basketball. An
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| interested in classical mythology and
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| | asteroid will have an odd shape, often
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| astronomy. No, Pluto is not named after
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| | like a potato, because its just not that
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| the lovable friend of Mickey Mouse, Pluto
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| | big. When a body is large enough to be
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| is the Roman god of the underworld. In
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| | squeezed into a round shape, its called
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| fact, Pluto the Disney dog was also
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| | hydrostatic equilibrium.
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| created in 1930 and named after the
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| | 3) The third thing they decided on also
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| planet Pluto!
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| | has to do with size. They agreed that an
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| Here are some more cool facts. Did you
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| | object must be big enough that its
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| know that Pluto is smaller than our moon?
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| | gravity removes other objects that occupy
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| And because its so small and far away,
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| | the same orbit. That means that as Pluto
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| even our strongest telescopes cant get a
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| | follows a certain path around the Sun, no
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| good picture of it. So you wont see it
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| | asteroids or other objects can occupy the
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| when youre star gazing, in fact no one
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| | same path around the Sun. But Pluto does
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| really knows what it looks like! But if
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| | not meet this criterion. Pluto is in a
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| all goes well, when the New Horizons
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| | section of our solar system called the
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| spacecraft flies by Pluto in 2015, we
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| | Kuiper belt which is made up of ice
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| will finally have up-close pictures of
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| | asteroids.
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| the most popular former planet. Have you
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| | So according to the IAU, Pluto meets only
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| memorized the planets and their order
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| | 2 of the 3 criteria and therefore is
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| from the sun? If not, heres an easy way
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| | considered a dwarf planet, along with
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| to remember: My (Mercury) Very (Venus)
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| | Xena (now Eris).
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| Educated (Earth) Mother (Mars) Just
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| | Also, Pluto has an orbit that is
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| (Jupiter) Served (Saturn) Us (Uranus)
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| | eccentric (oval-shaped), yet the other 8
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| Nine (Neptune) Pizzas (Pluto). This is
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| | planets have circular orbits. This is
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| called a mnemonic device (pronounced
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| | something that has bothered astronomers
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| ni-mon-ik) which means it helps your
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| | for a long time. It means that Plutos
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| memory. We have solar system model kits
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| | orbit brings it closer to the sun twice
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| that teach this and science activity
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| | during its 248 year revolution around the
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| books as well!
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| | sun. If you want to visualize this get a
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| In 2005, astronomers discovered what they
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| | pencil or Crayon and a piece of paper and
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| thought was the 10th planet, and
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| | first draw the sun, make it about the
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| temporarily named it after the TV
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| | size of a penny. Then draw a large circle
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| inspired character Xena (pronounced -
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| | around it. Try to make it as close to a
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| Zee-nuh) the Princess Warrior. In
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| | perfect circle as you can! This will be
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| September of 2006 they officially gave
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| | Neptunes orbit around the sun. Remember,
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| Xena the name Eris from the Greek goddess
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| | Neptune is the 8th planet from the Sun.
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| of discord and strife. Because Eris is
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| | Now draw an oval that overlaps Neptunes
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| about 5% bigger than Pluto, astronomers
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| | orbit so that two sides of the oval are
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| decided it was obvious that either they
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| | inside the circle and two sides are
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| are both planets, or they are both
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| | outside the circle. This is Plutos orbit.
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| something else. After Eris was discovered
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| | As you can see Plutos orbit comes closer
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| the IAU (International Astronomical
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| | to the sun than Neptunes. Its not one of
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| Union) decided to wait to make a decision
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| | the 3 planet criteria, but its an oddity.
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| on the status of Eris until it was
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| | Many people were very happy that Pluto
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| decided what a planet actually was.
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| | was no longer considered a planet, but
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| So what happened to Pluto? Why is it no
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| | other people were so upset they started
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| longer considered a planet? Believe it or
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| | petitions and websites to try and
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| not, this debate has been going on for a
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| | convince the IAU to reinstate Pluto as a
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| long time. In August of 2006, 424
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| | planet. There were even bumper stickers
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| astronomers finally got together to vote
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| | made up that said Honk if Pluto is still
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| on the definition of planet. The
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| | a planet!
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| definition they came up with would no
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| | So what do you think? Are you convinced
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| longer consider Pluto a planet, but
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| | that Pluto is a dwarf planet based on
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| rather a dwarf planet. The astronomers
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| | what the astronomers decided, or do you
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| decided on 3 criteria that make up a
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| | think Pluto should be a planet just like
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| planet:
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| | the other 8? This debate will likely go
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| 1) The object must be in orbit around the
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| | on for a long time!
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| Sun. Well, Pluto does that!
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|
