grrr… “so certainly all nuclei are NOT perfectly round”
What about flexible objects which are straight in their natural configuration? I could picture, for instance, some sort of seaweed which is anchored at the bottom, with a long stalk and a float at the top. It’s durable, and it’s naturally straight, but it could be easily bent.
Do you consider this crater round enough?
What about the rings of Saturn?
(OK, I know some of them are twisty or braided, but some are not)
For a straight edge, just cut a block of ice from the surface of a frozen lake.
That will have roughly the same curvature as the Earth’s surface.
Yes, it will. And if you can find something straighter than that in nature, go ahead and use it instead.
I don’t know how it compares against the straightness of metero crater ejecta on the Moon, but the Ninetyeast Ridge in the Indian Ocean is pretty durn long and straight.
I think we need to define what the limitations of “straight” and “circular” and “square” are going to be. Obviously, there isn’t such a thing as an actually physical circle or straight edge.
Oops, didn’t read rule number 4 of the OP. :smack:
Eyeballs are almost spherical
Venus barely rotates, and is closer to spherical than Earth, with equal polar and equatorial radii. From the reference given at that Wikipedia link (PDF), its radius is 6051.8 ± 1.0, and it’s maximum elevation is 11, or about 0.2 percent of the radius. The RMS error is about a tenth of that. Might be more nearly spherical than a neutron star, due to their rotation.
Spherical objects – raindrops are pretty perfect spheres. If you want something solid you can hold, meteorite bits that melt and reform in the air will be as perfect as the drops that form from a shot tower. They found lots of them in the vicinbity of the Tunguska meteorite. I’ll bet lots of micrometeorites (which you can harvest from your roof gutter, according to some people) are almost perfect spheres, too. Then there pleochroic halos. You can’t exactly handle them, but they’re hard as rocks, because they ARE rocks.
According to this article, the Sun beats any of the spherical objects mentioned on in this thread (although I’m sure that there are many (unmeasured) stars that are even more perfect spheres):
That’s a difference of about 7 parts per million; for comparison, Venus is about +/- 165 ppm off its average radius (figures given by ZenBeam).
By the way, this is a really old (zombie) thread, last posted in 6 years ago (and why do people keep signing up just to post on a thread that they should know is old?).
Only the smallest drops are close to spherical while larger drops become shaped like a hamburger bun before breaking apart:
(raindrops also fail the third point given by the OP; put a drop in your hand and it flattens out)
Google searches.
Raindrops can be mi;llimeters in diameter without flattening or breaking – this is confrmed by the light dustribution in some rainbows.
But what I’m wondering is, why do people sign up just to post; I come across many threads like this when I search but don’t try to register and post in them even if I see a reply that I want to respond to.
But are they really perfect spheres, plus there are the criteria given by the OP? Many of the other examples like Venus or the Sun will be much more perfectly round if shrunk to the size of a raindrop, which would have to have nanometer-scale precision.