Sirius is the brightest star in the night sky, shining much more brightly than other stars visible from Earth. Also known as the Dog Star, Sirius is located in the constellation Canis Major and is about 8.6 light-years away from us. Its brightness comes from its intrinsic luminosity and its relative closeness to Earth compared to other stars.

Sirius is actually a binary star system, consisting of a main sequence star (Sirius A) and a faint white dwarf companion (Sirius B). Its brightness makes it easily visible to the naked eye even in areas with some light pollution.

The other stars mentioned are bright but not as bright as Sirius:
- **Betelgeuse** is a red supergiant but appears less bright.
- **Rigel** is a blue supergiant star in Orion, also bright but not the brightest.
- **Polaris** is the North Star, famous for navigation, but it is not the brightest.

Knowing about Sirius helps us understand more about our night sky and star properties. Its brightness and proximity make it a key object of study in astronomy.

In summary, the brightest star visible at night from Earth is **Sirius**.