When you buy through links on our land site , we may gain an affiliate delegation . Here ’s how it works .
When you reckon up in the night sky , ourmoonis unmissable . Just like Earth , it ’s round and has a solid , rocky surface . But is our moon actually aplanet ?
The answer is technically no — at leastaccording to NASAand the International Astronomical Union ( IAU ) , animportant worldwide authority in uranology .
An object need to run across four criteria to be a major planet , per the IAU . It must be big enough that gravity pulls it into a gracious , pear-shaped shape and large enough to have cleared out all the asteroids and other debris from its orbit . It also needs to orbit the sun , and — significantly for the moon — a planet by definition is not a planet of another object .
The IAU ’s definition of a planet was finalized in 2006 . But that has n’t always been the consensus . The ancient Greeks , for illustration , retrieve the moon was a planet . ( They did also conceive the Earth was the center of the universe , though , so they were n’t quite right about a few thing . )
Even today , the IAU definition is a bit controversial . " Whether or not the moon is a satellite actually depends on who you ask,“Skylar Grayson , an astronomer at Arizona State University , told Live Science . The 2006 IAU definition " draw a fairly arbitrary line between planets and gnome planets that ( in)famously led to the demotion ofPluto , " she add . " Some planetary scientists thus elect to consider dissimilar definitions of planets , some of which include Pluto and the other dwarf planets , and others that even include the moon . "
relate : Why is Pluto not considered a major planet ?
Onealternate definition come from geophysics : A major planet ( or terrestrial body ) is anything massive enough to be round but small enough that it could n’t generate energy from nuclear fusion at any peak in its life . The first one-half of this definition divides planets from little bit of thesolar systemlike asteroids , and the 2nd one-half draws a line between major planet and stars . By this definition , the Earth would be a satellite — and so would the moon and Pluto .
— Planet Nine : Is the search for this elusive world nearly over ?
— How far forth is the moon ?
— Earth has extra lunation , and they may hold the secret of our solar system of rules ’s past
Most people think of a moonlight as something that ’s littler than a planet , especially the satellite it revolve . But this gets complicated , too . Our Sun Myung Moon is astonishingly big compare to our major planet — a whoppingone - one-fourth the size of Earth . AndPluto ’s biggest " moon , " Charon , is actually half the size of Pluto — big enough that it ’s often referred to as a binary planet instead of a moon . Looking beyond the solar system , astronomers have even founda moonshine as big as Neptuneorbiting a satellite the size of Jupiter about 8,000 unclouded - twelvemonth from Earth .
The IAU definition is the most widely accepted one for planethood , and it clearly state our synodic month is not a planet . However , " The vagueness around what is and is n’t a major planet point to how hard it can be to define condition in astronomy , " Grayson said . " Most things in the universe exist not in neat box but rather on a spectrum , and we have to decide where we want to draw the line between category . Sometimes those lines are agreed upon , and sometimes they ’re not . "
