About the image. Drawn as a red supergiant, coloured for a surface near 3 550 K (3 280 °C). Its size depends on its distance; the estimate used here is the current one, about 909 times the Sun.
For several years UY Scuti held an unofficial title: the largest known star. A 2013 study using interferometry measured it at about 1 708 times the Sun’s radius. Countless “biggest star in the universe” videos still use that figure.
Why it shrank
You cannot measure a star’s size directly unless you know how far away it is. The 2013 figure assumed a distance of about 2.9 kiloparsecs, a number that went back to a 1970 model of the star’s spectrum. Then the Gaia spacecraft measured the star’s position precisely enough to estimate its distance from parallax: the slight shift in its apparent position as Earth goes around the Sun. Gaia put UY Scuti much closer. A closer star of the same brightness must be smaller. Using Gaia’s later data, a 2023 study arrived at about 909 times the Sun’s radius, roughly half the old value.
Still enormous
909 solar radii is still huge. Placed where the Sun is, UY Scuti’s surface would reach past the asteroid belt, most of the way to Jupiter. It is a cool red supergiant in the constellation Scutum, shining with about 124 000 times the Sun’s power, and like other stars of its kind it is expected to end as a supernova.
Its story is a good example of how astronomy works: the measurement did not change, the ruler did.
To scale · radius, Sun = 1Sun: 1.00 · UY Scuti: 909
How hot is it?
Earth (average)288 K · 15 °C
Water boils373 K · 100 °C
Venus surface737 K · 464 °C
Iron melts1 811 K · 1 540 °C
Sun's surface5 772 K · 5 500 °C
UY Scuti3 550 K · 3 280 °C
UY Scuti: surface temperature. Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.
How long to get there?
UY Scuti is about 5 871 light-years away.
Light299 792 km/s5 871 years
Breakthrough Starshotplanned light sail, 20% of light speed29 355 years
Parker Solar Probefastest spacecraft so far, 192 km/s9.2 million years
Voyager 1leaving the Solar System, 17 km/s103.5 million years
At Voyager 1's speed the trip would take about 1 294 176 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Gallery
Artist's impressions rendered from the same model as the view at the top of this page.
Timeline
1956Classified as a red supergiant.
2013Measured at about 1 708 times the Sun's radius, assuming a larger distance.
2018Gaia's parallax places it much closer, shrinking the estimate.
2023Revised to about 909 times the Sun's radius.
Questions people ask
Is UY Scuti the biggest star?
Not any more. Better distance measurements cut its estimated radius from about 1 700 to about 900 times the Sun's.
How big is UY Scuti?
About 909 times the Sun's radius. In place of the Sun, its surface would reach past the asteroid belt.
Why did UY Scuti get smaller?
It did not change; the estimate of its distance did, and a star's size is calculated from its distance and brightness.