Hello from the Southeastern Planetarium Association. I’m currently at the SEPA 2015 and while I’m here I participated in a brief story-telling workshop where planetarians got together to share their favorite stories of the night sky. I chose to tell the story of the largest star ever observed (so far): UY Scuti.
I’ve never been too interested in constellations. What got me interested in science and astronomy was an episode of NOVA that I caught one night while I was 16. The program dealt with size comparisons of stars and planets and I walked away from it with my mind blown.
One of the things that people are obsessed with is size: what’s the largest planet, the largest asteroid, the largest galaxy, the largest star. And when you’re talking about stars, size really matters. After all, the only thing people have to compare stars to is our own star, the sun. And I’ve found that a lot of people still think that the sun is the largest star in the sky. Of course, we know, that this is not the case.
For a time, people thought that the biggest star ever found out in the cosmos was VY Canis Majoris. However, after continued research, scientists have found out that it’s not as large as once thought. That distinction goes to UY Scuti, a red supergiant located in the constellation Scutum—this constellation can be found just between Aquila and Sagittarius and it means “shield.” And I should point out that we shouldn’t confuse size with mass. Stars, after all, can be very large but not as heavy as some smaller stars. So let’s just confine this to sheer size.
If you could replace our sun with UY Scuti, you’d find that its photosphere would extend out past the orbit of Jupiter because it has a volume of 2.3 octillion miles. Beyond that, the hot atmosphere would extend out even further while the nebula and dust from the star would push past the orbit of Pluto.
Let’s put the size of this into perspective. If you walked around the Earth it would take you 1.4 years. If you were to walk around the sun it would take you 154 years. So how long would it take you to walk around UY Scuti? 320,000 years.
How about if you were to drive around it at an average speed? Just 9,500 years.
But no one would do that if you could take a plane. In a plane It would take you 1.8 days to fly around the Earth. At that rate it would take you 205 days to fly around the Sun. But to fly around UY Scuti, it would take you 1086 years.
Still not impressed? Well, light can travel around the Earth 7 times in one second. But for light to travel around UY Scuti it would take it 7.7 hours to travel all the way around.