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When you look up in the Nox sky , ourmoonis unmissable . Just like Earth , it ’s circular and has a solid , bumpy airfoil . But is our moon actually aplanet ?
The answer is technically no — at leastaccording to NASAand the International Astronomical Union ( IAU ) , animportant globose self-assurance in astronomy .
An target needs to meet four criterion to be a satellite , per the IAU . It must be freehanded enough that gravitational attraction pulls it into a skillful , round shape and big enough to have brighten out all the asteroid and other rubble from its orbit . It also demand to orbit the sunshine , and — importantly for the Sun Myung Moon — a planet by definition is not a artificial satellite of another aim .
The IAU ’s definition of a planet was finalized in 2006 . But that has n’t always been the consensus . The ancient Greeks , for instance , thought the lunation was a planet . ( They did also think the Earth was the center of the macrocosm , though , so they were n’t quite right about a few thing . )
Even today , the IAU definition is a fleck controversial . " Whether or not the moonshine is a satellite actually depends on who you ask,“Skylar Grayson , an uranologist at Arizona State University , order Live Science . The 2006 IAU definition " draws a fairly arbitrary line between planets and dwarf planet that ( in)famously led to the demotion ofPluto , " she added . " Some planetal scientists thus elect to study different definitions of planets , some of which include Pluto and the other dwarf planet , and others that even admit the moon . "
interrelate : Why is Pluto not turn over a planet ?
Onealternate definition comes from geophysics : A planet ( or planetary body ) is anything massive enough to be round but small enough that it could n’t generate energy from atomic nuclear fusion reaction at any compass point in its life . The first one-half of this definition separate satellite from smaller bite of thesolar systemlike asteroids , and the second half draws a blood between planets and sensation . By this definition , the Earth would be a satellite — and so would the moon and Pluto .
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Most masses think of a Sun Myung Moon as something that ’s belittled than a planet , especially the planet it orb . But this gets complicated , too . Our moonshine is astonishingly with child compared to our satellite — a whoppingone - quarter the size of Earth . AndPluto ’s large " moon , " Charon , is actually half the size of Pluto — big enough that it ’s often referred to as a binary satellite alternatively of a moon . Looking beyond the solar organisation , stargazer have even founda moon as liberal as Neptuneorbiting a planet the size of Jupiter about 8,000 idle - long time from Earth .
The IAU definition is the most widely admit one for planethood , and it clearly states our moon is not a satellite . However , " The vagueness around what is and is n’t a planet points to how severely it can be to define term in uranology , " Grayson suppose . " Most things in the universe exist not in neat corner but rather on a spectrum , and we have to determine where we require to eviscerate the lineage between category . Sometimes those lines are agreed upon , and sometimes they ’re not . "
