Playing off a similarly titled thread.
The real questions I ask are: Why does Jupiter have an edge?, why does the Sun, and why do cumulus clouds?
Solid things have edges because there are forces sticking the components of the thing together. Mercury has an edge because the solid matter is attracted towards the center.
But what about gaseous things like the Sun and Jupiter? When you see photos of these, it does not seem that there are volumes of decreasing density as you move away from the center.
I have a similar question about clouds in the earth’s atmosphere. Here, it does sometimes seem that there is a more solid, or more white area in the center of the cloud, and then there are wispier protubrances further from the center. But even for clouds it does seem strange to me that there are any that look like cumulous clouds: There is sky, and then there is a cloud, looking like a popcorn kernel. It seems like there is a discontinuity in the density of the cloud.
In the case of Jupiter, I can imagine that there are spherical shells of gas of decreasing density. Since the shells are spherical, you can’t see any bumpiness as you would in a cloud. Is the edge of Jupiter just the point where the density falls below some limit to change the optical properties of the gas?
I know about solar prominences, so in some sense I guess the Sun doesn’t have an edge like Jupiter. Why isn’t the sun bumpier?