uranus. uranus. represented by a bocce ball. you ever play bocce? no, i've never played bocce. neither have i. (both laugh) tyson: it would take 22 plutos on a chain to equal the diameter of one uranus. croquet, anyone? what do you have now? neptune. neptune. why don't you have the honor? tyson: big blue neptune is 21 times as wide as pluto. last and least? and not least. we have pluto. represented by a ball bearing removed from a roller skate. ah. sometimes the most valuable things are in the smallest packages. there you go. excellent. pluto. tyson: pluto's diameter is just under 1,500 miles. in fact, if it ever decided to visit america it would stretch only from california to kansas. no matter how you look at it pluto makes a scrawny little planet. pluto's really puny, right? but so is mercury. pluto's a lot punier-- 1/20th the mass of mercury. of mercury. gingerich: that's less than the mass of the moon. touchdown right there. (laughing) tyson: if we were to keep score of pluto's oddball traits versus its planetlike characteristics, how would it add up? brian thinks pluto's

william herschel pointed his telescope in the sky and found uranus-- uranus. uranus is a major part of the solar system. and he found it. that is a pretty big deal. i discovered a little ice ball out on the fringe and it just didn't seem like the same magnitude of a discovery. and i had been struggling with this for years. like, what do you do when you finally find one bigger than pluto? i did not believe that astronomers had the guts to ever demote pluto, because it's just too publicly painful. tyson: and if tiny pluto was a planet, shouldn't mike's discovery be one too? so he forged ahead, ultimately selecting a clever name for his discovery: eris, the greek goddess of discord and strife. eris instilled jealousy and envy among men, driving them to battle. mike's choice perfectly captured the destabilizing effect eris was destined to have on pluto, although he couldn't have guessed what was about to happen next. for the past century, the iau, the international astronomical union, has been in charge of naming celestial objects. but it couldn't approve the name

trawls and some of the other slaves here on the estate -- freeing charles and some of the other slaves uranus state, but he by slaves, and too. he spends time at the markets here in lexington, purchasing slaves, and is known for the quality of sleeves that he purchases. again, he is one of those people with a dual nature. >> people used to talk about slavery in kentucky being the mildest but it did not really matter. it was still slavery. abolitionists came to kentucky and say that slavery is the mildest, but it was still enough here to cause the heart the second. that is really what slavery was. they heard the last on the back and the screams of the slaves, and that was the death knell of liberty. and alice the part of clay that he could never quite pick up on as much as the other parts of his life. >> i want to spend more on the american colonization society. i read that at the first meeting, some famous american names around the table, including andrew jackson, his nemesis, and daniel webster, james monroe, francis scott key, who wrote the star spangled banner, how popular was the american