The true differences in stellar size are hidden from the naked eye. Our Sun is a medium-sized star, yet over a million Earths could fit inside its volume. Among the cosmos’ giants is Betelgeuse, a luminous beacon visible in the constellation Orion. This colossal star is so immense that comparing it to Earth requires a journey into astronomical volume. Understanding the sheer scale of Betelgeuse begins with grasping its fundamental nature and why it has grown so large.
Defining Betelgeuse: The Red Supergiant
Betelgeuse, officially Alpha Orionis, is a red supergiant star located hundreds of light-years away in the shoulder of the constellation Orion. This classification indicates the star is in an advanced stage of its stellar life cycle. Stars like Betelgeuse begin as massive, hot, blue stars, rapidly burning through their hydrogen fuel.
Its enormous size results from exhausting the hydrogen fuel in its core. When hydrogen fusion ceases, the core contracts under gravity, increasing the temperature until it ignites helium. This renewed energy forces the star’s outer layers to expand dramatically, transforming it into the cool, luminous red supergiant we observe today. The star is now burning helium and is nearing the end of its stellar existence.
Calculating the Scale: Earth Volume Comparison
Determining Betelgeuse’s exact size is challenging because it is a pulsating star, unlike our stable Sun. Its outer layers constantly expand and contract, causing the radius to vary significantly over time. Estimates often center around 764 times the radius of the Sun, but this figure can range from 640 to over 887 solar radii depending on its current pulsation phase.
To calculate how many Earths fit inside, astronomers compare the volume of a sphere, which is proportional to the cube of its radius. The Sun’s radius is about 109 times greater than Earth’s radius. Using the estimate of 764 solar radii for Betelgeuse, its radius is over 83,000 times larger than Earth’s radius (764 x 109).
Cubing this ratio provides the final volume comparison. Based on lower-end radius estimates, Betelgeuse’s volume can contain approximately 600 trillion Earths. If the star were at the larger end of its measured size range, that number could increase to well over one quadrillion Earths.
Visualizing the Immensity within Our Solar System
The best way to comprehend the scale of 600 trillion Earths is to place Betelgeuse directly into our solar system, replacing the Sun at its center. If this cosmic swap occurred, the star’s visible surface, or photosphere, would instantly engulf the orbits of all the inner planets. Mercury, Venus, and Earth would be swallowed by the star’s immense outer atmosphere.
The expansion would continue outward, entirely absorbing the orbit of Mars. The star’s surface would then extend deep into the main asteroid belt, past the Mars-Jupiter orbital gap. Using the radius estimate of 764 solar radii, Betelgeuse would extend to roughly two-thirds of the distance to Jupiter’s orbit.
Even at its conservative size, the star’s outer edge would sit about 3.6 Astronomical Units (AU) from the center. One AU is the distance from the Earth to the Sun. Some measurements suggest Betelgeuse could swell large enough to completely engulf Jupiter’s orbit, extending nearly 5.5 AU from the center. This visualization shows that the star’s sheer size would rewrite the entire architecture of our solar system.