Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey
Speaker 1: brain Stuff, Lauren Bogle bomb here with another classic episode
Speaker 1: from our archives. This one deals with one of the
Speaker 1: most simple sounding yet cosmically impressive concepts that we humans
Speaker 1: can contemplate. Why are stars and planets all nearly spherical? Hi,
Speaker 1: brain Stuff, Lauren bog O bomb here. It's something we
Speaker 1: kind of take for granted. Roses are red and planets
Speaker 1: are spherical. That's just the way things are, right, after all,
Speaker 1: Building model solar systems would be way more challenging if
Speaker 1: instead of using little foam balls we had to make
Speaker 1: a bunch of do decahedron shaped planet models. But have
Speaker 1: you ever wondered why planets look like this? Why are
Speaker 1: they basically spherical and not say, cylindrical or cube shaped?
Speaker 1: We should kick off this discussion by calling a spade
Speaker 1: a spade. None of the planets in our solar system
Speaker 1: are perfect spheres, nor, for that matter, is our Sun.
Speaker 1: All those bodies could be more accurately described as oblate
Speaker 1: spheroids objects with the shape bulge slightly around the middle.
Speaker 1: To borrow an analogy from the astronomer philled plate, they
Speaker 1: look like a basketball that someone is sitting on put
Speaker 1: More technically, in a celestial body with an oblate spheroid shape,
Speaker 1: the polar circumference will be smaller than the equatorial one.
Speaker 1: So here on Earth, if you were to travel from
Speaker 1: the north pole to the South pole and back, you'd
Speaker 1: have walked a grand total of twenty four thousand, eight
Speaker 1: hundred and twelve miles that's thirty nine thousand, nine hundred
Speaker 1: and thirty one kilometers. On the other hand, a complete
Speaker 1: trip around the equator would be a bit longer. That's
Speaker 1: because the circumference of Earth's equator is twenty four thousand,
Speaker 1: nine hundred miles or forty thousand and seventy kilometers. As such,
Speaker 1: when you stand at sea level on the equator, you're
Speaker 1: further away from the center of our planet than you
Speaker 1: would be at either the north or South pole. On
Speaker 1: some other planets. This bulge is even more pronounced. Just
Speaker 1: look at Jupiter. Earth is only zero point three percent
Speaker 1: wider at the equator than it is from poll to poll,
Speaker 1: but Jupiter's measurements showcase a much bigger disparity. Astronomers have
Speaker 1: found that this plus sized planet is a full seven
Speaker 1: percent wider at its equator than it is between the polls.
Speaker 1: The oblate spheroid shape is the result of two main factors,
Speaker 1: gravity and rotation. Troy Carpenter, director of Washington State's Goldendale Observatory,
Speaker 1: recently discussed the matter with us in an email exchange.
Speaker 1: They explain, everything which has mass experiences gravity, and gravity
Speaker 1: attempts to crush an object inward in all directions. That's
Speaker 1: because all objects experience self gravity, a force which pulls
Speaker 1: their atoms toward a common center. As the mass of
Speaker 1: an object increases, so too does its self gravitational pull.
Speaker 1: After it exceeds a certain mass, the pull gets overpowering
Speaker 1: to the point where the object collapses into itself and
Speaker 1: becomes spherical. Little items, like say a banana or a
Speaker 1: lug wrench, can resist this fate because their self gravity
Speaker 1: is relatively weak, allowing them to retain non spheroid shapes. However,
Speaker 1: in planets, suns, and other truly massive bodies, the force
Speaker 1: is so strong that they can't avoid being distorted into
Speaker 1: sphere roids. But Carpenter said gravity is not the whole story.
Speaker 1: While gravity conspires to render the planet's spherical, the speed
Speaker 1: of their rotation is simultaneously trying to flatten them. The
Speaker 1: faster a celestial body spins, the more disproportionate it's equatorial
Speaker 1: bulge gets. Carpenter tells us this is why there are
Speaker 1: no perfect spheres in our Solar system, only oblate spheroids.
Speaker 1: The Sun is almost a perfect sphere due to its
Speaker 1: immense gravity and relatively slow rotation rate of twenty five days.
Speaker 1: A significant percentage of stars in the sky rotate much
Speaker 1: faster and bulge noticeably at their equators. One such star
Speaker 1: is all Tear, located just sixteen point eight light years
Speaker 1: away from our home planet. It's among the brightest objects
Speaker 1: in the night sky. All Tear is also notable for
Speaker 1: spinning very very fast. It completes a full rotation on
Speaker 1: its axis every ten point four Earth hours. Accordingly, astronomers
Speaker 1: estimate that All Tears at least fourteen percent wider at
Speaker 1: the equator than it is from poll to poll. Rotational
Speaker 1: speed also explains Jupiter's bulge. After all, a day on
Speaker 1: this gas giant is a brisk nine point nine earth
Speaker 1: hours long. Other forces act upon the stars and planets
Speaker 1: as well, altering their shapes. Although Earth is an oblate spheroid,
Speaker 1: it certainly isn't a perfect one. The gravitational pull of
Speaker 1: the Sun and Moon both influence the planet's shaped to
Speaker 1: a degree. For that matter, so do Earth's own plate
Speaker 1: tik toonics. Consequently, the mass of our home world isn't
Speaker 1: evenly distributed. In fact, it's sort of lumpy. Still, it
Speaker 1: looks a good deal rounder than Jupiter and Saturn. In turn,
Speaker 1: the planets in our universe appear way more spherical than
Speaker 1: some of their moons do. Mars, for instance, has two
Speaker 1: small satellites, neither of which has a self gravity to
Speaker 1: be pulled into an oblate spheroid. Instead, their appearance is
Speaker 1: often described as potato shaped. In conclusion, will say this
Speaker 1: much for our home planet. It may not be flawless,
Speaker 1: but at least the place is fairly well rounded. Today's
Speaker 1: episode was originally produced by Tristan McNeil and is based
Speaker 1: on the article why our planets almost sphere on how
Speaker 1: stuff Works dot Com, written by Mark Vancini. Brain Stuff
Speaker 1: is production of iHeart Radio in partnership with how stuff
Speaker 1: Works dot Com, and is produced by Tyler Clang. For
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