The vastness of space often defies human comprehension, making comparisons between celestial bodies a common way to grasp the scale of the cosmos. Understanding the physical relationship between a star and a planet requires moving beyond simple linear measurements like diameter and focusing on the three-dimensional space they occupy. This volumetric comparison illustrates the true immensity of the solar system’s largest resident, the Sun, relative to one of its outermost planets, the ice giant Uranus. By comparing the capacity of the Sun’s interior to the volume of Uranus, we can gain a tangible appreciation for the tremendous size difference between our star and the planets that orbit it.
The Direct Numerical Answer
The sheer difference in size between a star and a planet leads to a number that powerfully conveys the magnitude of the Sun. If the Sun could be hollowed out and filled with planets the size of Uranus, it would hold approximately 22,000 of them. This figure immediately establishes the extraordinary scale of our star, which contains 99.8% of the entire mass of the solar system. Visualizing a sphere packed with over twenty thousand planetary bodies, all the size of Uranus, helps to contextualize the Sun’s dominance. The number itself is a testament to the immense volume contained within the star’s atmosphere. This dramatic numerical result is a direct consequence of the star’s enormous diameter compared to the planet’s relatively modest size.
Comparing the Dimensions of Uranus and the Sun
The vast numerical difference is rooted in the physical dimensions of the two celestial objects, starting with their radii. Uranus is a large planet, classified as an ice giant, with a mean radius of approximately 25,362 kilometers. This means Uranus is nearly four times the diameter of Earth, making it the third-largest planet in the solar system. To put this into perspective, if Earth were the size of a large apple, Uranus would be comparable to a basketball. The Sun, however, has a mean radius of about 696,340 kilometers, making it approximately 27.5 times wider than Uranus.
This immense difference in diameter is where the true scale of the Sun becomes apparent. The Sun’s diameter is large enough that 109 Earths could be lined up across its face, and it is so massive that all the planets combined barely register against its bulk. Unlike the rocky terrestrial planets or even the gas giants, Uranus is primarily composed of various ices, such as water, ammonia, and methane, surrounding a denser core. The Sun, a plasma ball of superheated hydrogen and helium gas, is a different class of object entirely, which accounts for its overwhelming size in the solar system.
How the Calculation is Determined
The process for determining how many planets fit inside a star relies on a comparison of their respective volumes, not their diameters. Volume is a measure of the three-dimensional space an object occupies. The calculation involves finding the volume of the Sun and the volume of Uranus and then dividing the former by the latter. Since both celestial bodies are roughly spherical, this mathematical approach provides a close estimate of the fit number.
The number of Uranus-sized planets that fit inside the Sun is approximately the cube of the ratio of their radii. Because the Sun’s radius is roughly 27.5 times greater than the radius of Uranus, cubing this ratio yields the volumetric fit number of about 20,700. This result is always an approximation because neither the Sun nor Uranus are perfect spheres, as both are slightly flattened at the poles due to rotation. Furthermore, the Sun does not have a distinct, solid surface, so the exact boundary used for its volume measurement is the point where its gases become opaque.