What's the longest, naturally-occurring straight edge, circle, and sphere?

Factual Questions
1

It is very unusual to find perfect circles or straight lines in nature. But are there any reasonably perfect approximations?

The rules are as follows:

[ul]It has to naturally occuring–not man made. [/ul]

[ul]It has to occur as a repeatable natural process. A single, unique object wouldn’t count. [/ul]

[ul]It has to be durable. Something that could be held without deforming it. So things like bubbles and spider silk wouldn’t count.[/ul]

[ul]Perfection doesn’t need to be perfect, just reasonable. As straight as a ruler, as circular as I could draw with a compass, as spherical as a ball. [/ul]

I can’t think of any natural object that I would consider a perfect circle or sphere. Maybe there’s an animal with a perfect circle for an eye socket or something?

As for a straight edge, I would guess it would be some sort of crystal. Like the Blahblah Quartz usually grows to a length of 6 inches or whatever.

2

They’re so smooth that the only thing rounder is a neutron star.
So at about 20 km diameter, the silhouette of a neutron star is the largest really, really accurate natural circle.

3

Those are handmade though.

4

Yeah, the ref was to the stars, which are a natural form.

5

Yeah, but although you could, technically, hold it in your hand without deforming it, that would probably be undesirable in the extreme. Killing the ref costs you serious points.

6

The earth is actually closer to a perfect sphere than your average billiard ball, even with all the mountains and oceans and whatnot.

7

But is it a perfect sphere though? Most bodies in space are oblate spheroids, ie wider at the equator and flatter at the poles. Are neutron stars an exception?

8

Neutron stars are objects of extremely high density (10[sup]12[/sup] kilograms per cubic centimeter, according to Wikipedia - they contain several solar masses with a diameter of about 20 kilometers), according to and extremely high gravitational forces, which cause the star to tend to the form of a sphere. In the case of the Earth, the oblate form is caused by centrifugal forces at the Equator, but those are too weak to match the much stronger gravitation in a neutron star.

9

My last post was messed up. Here is how it was intended to read:

Neutron stars are objects of extremely high density (in the order of 10[sup]12[/sup] kilograms per cubic centimeter, according to Wikipedia - they contain several solar masses with a diameter of about 20 kilometers), and extremely high gravitational forces, which cause the star to tend to the form of a sphere. In the case of the Earth, the oblate form is caused by centrifugal forces at the Equator, but those are too weak to match the much stronger gravitation in a neutron star.

10

The OP said durable, and merely gave an example of what might be durable. A neutron star is quite durable by any definition.

11

Take the cross-section through the equator, rather than the pole.

12

Now for straight lines…this could get trickier.

I vote for the rays of impact craters, like on the earth’s moon. Nice, long, straight, and pretty.

And the squarest object in nature is, of course, Regis Philbin.

13

I was wondering more about things we might find a little closer to home. So one more rule is that it has to be found on Earth.

14

What about a string with a weight hanging on the end? That’s straight, but I don’t know if it counts as natural.

15

How about the basalt crystals at the Giant’s Causeway?

16

Is an atomic nucleus round? According to Wiki the neutrons and protons are held together by a nuclear force far stronger than gravity.

17

A pebble dropped in a still pond produces a perfect circle. Some of the American transcendalists were stimulated by that, I think.

18

ThaNKS FOR THE INFO, **Schnitte **

19

But not a durable one, though.

20

The nuclei of unranium and transuranics are classically described as (American) football shaped, so certainly all nuclei are perfectly round. I’m not sure if any are, but that probably doesn’t meet the OPs criteria, because the ‘surface’ of a nucleus is a problematic construct, largely a matter of definition.

Besides, it’s pretty rare for an atomic nucleus to qualify as the largest anything.