Here's why:

* Sirius is the brightest star in the night sky, with an apparent magnitude of -1.46.

* Rigel is the seventh brightest star in the night sky, with an apparent magnitude of 0.12.

Apparent magnitude is a measure of how bright a star appears from Earth. Lower numbers indicate brighter stars.

While Rigel is a much larger and more luminous star than Sirius, it's farther away from Earth, making it appear dimmer in our sky.