1. By Mass:
* UY Scuti: This red supergiant is the largest star by mass we know of, with about 30 times the mass of our Sun. It's about 1,700 times the Sun's diameter, so if it were in our solar system, it would extend out to Jupiter's orbit!
2. By Diameter:
* UY Scuti: As mentioned above, it's also the largest star by diameter, with a radius around 755 times larger than our Sun's.
So, UY Scuti is the largest star by both mass and diameter that we currently know of. However, it's important to remember that we are constantly learning more about the vastness of space, and there might be even larger stars out there waiting to be discovered.
