It's not a single planet, but rather Venus is generally considered the most brilliant object in the sky after the Sun and Moon.

Here's why:

* Close to Earth: Venus orbits closer to the Sun than Earth, making it appear brighter.

* Highly reflective: Venus has a thick atmosphere of carbon dioxide and sulfuric acid clouds, which reflects a large amount of sunlight.

While other planets like Jupiter and Mars can appear bright, Venus's close proximity and highly reflective surface make it the most brilliant in the sky.