Planet and star sizes: choosing the right comparison
A shared diameter scale makes enormous differences visible. Interpreting it requires separating size from distance, volume from mass, and a convenient spherical model from the shapes of real worlds.
Why use mean diameter for Earth and Jupiter?
Neither planet is a perfect sphere. Equatorial and polar diameters differ, especially for rapidly rotating Jupiter, so a quoted diameter needs a definition. Rounded mean diameters give this comparison a consistent reference. They are useful for understanding relative size, while detailed work would also account for oblateness and the measurement convention.
How do diameter ratios become volume ratios?
For a spherical approximation, volume grows with the cube of diameter. The displayed solar and terrestrial diameters give a ratio of about 109.3, whose cube is about 1.31 million. That result compares volumes; it does not describe a literal arrangement of separate Earth-sized spheres inside the Sun. Packing spheres would introduce gaps.
Why is a size comparison different from a solar-system map?
The gaps between the illustrated objects are chosen to keep them readable. They carry no orbital-distance information. Treat the disks as objects placed beside a shared ruler rather than positions in space: changing the viewing scale preserves their diameter ratios, but cannot turn the layout into a map of their real separation.
Does a larger volume mean the same increase in mass?
Mass depends on both volume and average density. Earth, Jupiter and the Sun differ in composition and internal structure, so a diameter or volume ratio is not also a mass ratio. The Sun’s visible boundary is associated with its photosphere rather than a solid surface. These limits matter when interpreting a comparison built from simple circles.
Dive deeper
From diameter to volume
For spheres, volume is proportional to diameter cubed. Using the displayed rounded diameters gives a linear ratio of about 109.3 and a volume ratio of about 1.31 million. This geometrical ratio does not imply the same mass ratio, because average densities differ.
V₁ / V₂ = (D₁ / D₂)³ ≈ (1,392,700 / 12,742)³ ≈ 1.31 millionA useful approximation, with clear limits
Earth and especially Jupiter are oblate. The Sun has no solid surface: its visible boundary is associated with the photosphere. Rounded mean diameters and circles make comparison readable; they do not depict detailed planetary shape or atmospheric boundaries.
Good questions.
Are the distances also to scale?
No. Only diameters share a physical scale. Real orbital distances are far larger than the gaps shown here. This is a size comparison, not a map of the solar system.
Why do different references give different Jupiter diameters?
Jupiter bulges at its equator and is flattened at its poles. Mean, equatorial and polar diameters are different. This exhibit uses a rounded mean diameter for a clearly defined comparison.
Could 1.3 million Earths literally fit inside the Sun?
The familiar number describes an approximate volume ratio. Packing separate spheres leaves gaps, and the Sun’s interior is plasma rather than an empty container. It is a comparison of volumes, not a literal packing result.