Stephenson 2-18 (St2-18) is currently the largest known star, dwarfing even the well-known giants like Betelgeuse and UY Scuti. But just how massive is this celestial behemoth compared to our tiny Earth? The answer is staggering: Stephenson 2-18 is so large that if placed in our solar system, it would extend beyond the orbit of Saturn.
stephenson 2-18
A Star of Immense Proportions
Stephenson 2-18 is classified as a red supergiant or possibly even a red hypergiant star, residing in the constellation Scutum approximately 18,900 light-years from Earth. Its estimated radius is a mind-boggling 2,150 times that of our Sun. To put that into perspective:
- Solar Radius: The Sun’s radius is about 432,000 miles (695,000 kilometers).
- Stephenson 2-18’s Radius: Multiplying the Sun’s radius by 2,150, we get Stephenson 2-18’s radius of roughly 930 million miles (1.5 billion kilometers).
Earth’s Insignificance
Earth’s radius is a mere 3,959 miles (6,371 kilometers). Comparing this to Stephenson 2-18’s immense size reveals a truly humbling difference. The star is approximately 235,000 times larger than Earth in terms of radius. If Stephenson 2-18 were a hollow sphere, it could contain over 13 quadrillion Earths!
Visualizing the Scale
Imagine shrinking the Sun down to the size of a basketball. On this scale, Earth would be about the size of a pinhead. Stephenson 2-18, however, would be a colossal sphere roughly 150 feet (46 meters) in diameter – larger than a standard Ferris wheel. This illustrates the truly enormous scale of this star.
Beyond Saturn’s Orbit
Saturn orbits the Sun at an average distance of about 886 million miles (1.4 billion kilometers). Stephenson 2-18’s radius surpasses this distance, meaning that if it were placed in our solar system where the Sun is, its surface would extend well beyond Saturn’s orbit, engulfing Mercury, Venus, Earth, Mars, Jupiter, and Saturn.
A Record-Breaking Star
Stephenson 2-18’s discovery dethroned previous record holders for the largest known star, including UY Scuti and WOH G64. While uncertainties remain regarding its exact size and properties, its immense scale is undeniable. This red supergiant stands as a testament to the vastness and diversity of the universe, reminding us of the truly awe-inspiring scales of celestial objects compared to our own planet.
The image depicts one of the largest stars known, Stephenson 2-18, and its supposed and debated parent cluster, Stephenson 2, which contains numerous red supergiant stars. Stephenson 2-18 is a large, luminous, and unusually cool red supergiant or even red hypergiant. In this infrared image from the IRAC HEALPix from the Spitzer Space telescope’s missions, Stephenson 2-18 glows bright, as it has immense infrared excess caused by dramatic mass loss events. Numerous other large and luminous stars are also depicted, including Stephenson 2-DFK 49, a possible post-red supergiant star, IRAS 18357-0604, a yellow hypergiant and Stephenson 2-03 or Stephenson 2-DFK 2, another large and unusually cool red supergiant. Image credit: IRAC HEALPix survey in color from the Spitzer Space Telescope (CC BY-SA 4.0)
Stephenson 2 location, image: Wikisky
