________ is the brightest planet in the Solar system.

Concept

How bright a planet appears in our sky (its apparent brightness) is governed by three factors: how much sunlight its surface or atmosphere reflects (its albedo), how large it appears (its size and how close it is to Earth), and how close it is to the Sun (which sets how much sunlight reaches it). A planet with a high albedo that also lies near both the Sun and the Earth will outshine the others.

Applying it

Venus wins on every count: it is wrapped in a dense, unbroken layer of sulphuric-acid clouds that reflect about two-thirds of the sunlight falling on them (an albedo near 0.65, the highest of any planet). It is the Sun's second planet, so it receives intense sunlight, and it is the planet that comes closest to Earth. The combination of very high reflectivity plus nearness makes Venus the most brilliant planet, outshone in the night sky only by the Moon.

Contrast

• Mars reflects relatively little light from its dusty, rocky surface and appears as a modest reddish point, far dimmer than Venus.

• Saturn is enormous but lies very far from both the Sun and the Earth, so the sunlight it receives and returns to us is weak, leaving it faint.

• Jupiter is the largest planet and can shine brightly, but its greater distance keeps it below Venus in apparent brightness.