A star that is millions of times brighter than the Sun is called a supergiant.

Here's why:

* Supergiant: These stars are incredibly large and luminous, with masses typically 10 to 50 times that of the Sun. They burn through their fuel much faster and have much shorter lifespans than smaller stars.

* Brightness: Supergiants are incredibly bright, some reaching millions of times the luminosity of the Sun.

Examples of supergiants include:

* Betelgeuse: A red supergiant in the constellation Orion.

* Rigel: A blue supergiant in the constellation Orion.

* Deneb: A white supergiant in the constellation Cygnus.

Let me know if you have any other questions!