How Big Is UY Scuti Compared to the Sun?

Updated on September 07, 2025 | By Jameswebb Discovery Editorial Team 

Exploring the colossal size of UY Scuti and how it compares to our Sun in radius, volume, brightness, and fate. 

When people ask, "What is the largest star in the universe?" the name UY Scuti almost always comes up. This colossal red supergiant, located thousands of light-years away in the constellation Scutum, has captured the fascination of astronomers and the public alike. But just how big is UY Scuti compared to our Sun — the star that makes life possible on Earth?

In this detailed article, we will explore everything about UY Scuti’s immense size, how it stacks up against the Sun, its place in the cosmic hierarchy, and what its sheer scale means for our understanding of stellar evolution.

Quick Facts About UY Scuti

• UY Scuti is a red supergiant star.

• It lies in the constellation Scutum.

• It is about 9,500 light-years away from Earth.

• Its radius is estimated to be between 1,700 and 1,900 times the Sun’s radius.

• It shines about 340,000 times brighter than the Sun.

• It was first catalogued in 1860 by German astronomers.
  
  

Understanding Stellar Size

When astronomers talk about a star’s size, they often refer to its radius, diameter, volume, and mass.

• Radius: the distance from the star’s center to its surface.

• Diameter: twice the radius.

• Volume: the total space the star occupies.

• Mass: the amount of matter the star contains.
  
  

To compare stars easily, scientists use solar units. One solar radius means one Sun’s radius.

UY Scuti vs the Sun

The Sun is huge to us, yet compared to UY Scuti, it looks tiny.

• Radius: The Sun’s radius is about 696,000 kilometers. UY Scuti’s radius is about 1.2 billion kilometers. That is roughly 1,700 times larger.

• Diameter: The Sun’s diameter is about 1.39 million kilometers. UY Scuti’s diameter is about 2.4 billion kilometers.

• Volume: UY Scuti could hold around 5 billion Suns inside it.

• Brightness: UY Scuti is about 340,000 times more luminous than the Sun.
  
  

If UY Scuti were placed at the center of our Solar System, its surface would extend past Jupiter’s orbit. The Sun, by comparison, only stretches a small fraction of that distance.

Why Is UY Scuti So Big?

UY Scuti is in the red supergiant stage of its life. When massive stars run out of fuel, their cores shrink under gravity while their outer layers expand enormously. This expansion makes the star huge but less dense.

UY Scuti has a surface temperature of about 3,365 Kelvin, cooler than the Sun’s 5,778 Kelvin. But because of its size, it still shines extremely bright.

Is UY Scuti the Largest Star?

Other giant stars also compete for the title.

• Betelgeuse: About 1,000 times the Sun’s radius, smaller than UY Scuti.

• VY Canis Majoris: Between 1,420 and 2,200 times the Sun’s radius.

• Stephenson 2-18: Possibly larger than UY Scuti, with estimates around 2,150 times the Sun’s radius.

So, UY Scuti is one of the largest stars known, though not always ranked the absolute largest.

Mass and Gravity

Surprisingly, being larger does not mean UY Scuti is more massive than billions of Suns. Its estimated mass is about 30 to 40 times that of the Sun. Its outer layers are very spread out and do not add much to the total mass.

The Sun’s surface gravity is much stronger. On UY Scuti’s surface, gravity would feel far weaker.

Brightness Compared to the Sun

Even though UY Scuti is cooler, it shines far brighter because of its size. It is about 340,000 times more luminous than the Sun. If it replaced our Sun, Earth would be burned instantly, long before being swallowed.

The Future of Both Stars

• The Sun: In about 5 billion years, the Sun will expand into a red giant, engulfing Mercury and Venus, and possibly Earth. It will later shrink into a white dwarf.

• UY Scuti: Much sooner, it will explode as a supernova. The explosion may leave behind a neutron star or black hole.
  
  

What If UY Scuti Replaced the Sun?

If UY Scuti sat where the Sun is now, it would swallow Mercury, Venus, Earth, and Mars. Its surface might even reach near Jupiter’s orbit. Planetary orbits would be destroyed, and life on Earth would end instantly.

Can We See UY Scuti?

Although extremely large, UY Scuti is about 9,500 light-years away. Its brightness in our sky is too faint for the naked eye, but it can be observed with a medium telescope under dark skies.

Why UY Scuti Matters

Studying UY Scuti helps astronomers understand the life cycles of massive stars, how heavy elements form in supernova explosions, and what limits exist for star size. This knowledge is also important for astrobiology, since elements created in these massive stars are vital for life.

FAQs

Is UY Scuti the largest star?
It is one of the largest, though Stephenson 2-18 may be bigger.

How many Suns can fit inside UY Scuti?
About 5 billion Suns could fit inside its volume.

Can we see UY Scuti without a telescope?
No, it is too faint. A telescope is required.

How hot is UY Scuti?
Its surface temperature is about 3,365 Kelvin, cooler than the Sun.

Will UY Scuti explode?
Yes. Within a few million years, it will end in a massive supernova.

Final Thoughts

The Sun is vital to us, but in the universe it is an ordinary star. UY Scuti shows us the extreme end of stellar growth — a true giant that makes our Sun look small. By studying it, scientists learn more about star evolution, element formation, and the grand scale of the cosmos.