The planets are a passionate bunch, and as seen from Earth throughout the year, these celestial bodies appear moving across the sky and brighten and fade in turn. A planet’s distance from Earth is the main factor in its brightness. Last October, Mars showed brighter than Jupiter because it was close to Earth, and it will be until 2035. Into the western sunset sky, Mars is now sinking, falling deeper into the brightening twilight glow because Mars and Earth are practically the opposite sides of the Sun.
The planet’s distance from the Sun also affects its overall brightness, determining the intensity of sunlight illuminating its surface. When the two brightest planets Jupiter and Venus in our sky, appear near to each other when examining through a telescope and people can notice that the disk of Venus appears much brighter than that of Jupiter, and this is partly because it is closer to us, but mainly because it’s also more than seven times more compared to the Sun.
Another factor is the size of the planet. For example, Mars is only about twice as prominent as Earth’s Moon, and when it gets further away, it tends to diminish in brightness faster than more giant planets like Venus. Another factor is the planet’s phase, the portion of its sunlit hemisphere turned toward the Earth. The two planets nearer to Sun than EarthVenus and Mercury display a complete cycle of phases like Earth’s Moon. Around the time of quadrature Mars appears significantly gibbous, 90 degrees to the east or west of the Sun. Saturn and Jupiter show only a slight gibbous effect, mainly because of their much greater distances from the Sun and the Earth.
Another factor could be the planet’s albedo or reflectivity. This factor depends upon the planet’s surface, including dark and light areas that may rotate into and out of view. Venus albedo is very high compared to other planets at around 70%, and this is because of its blanket of highly reflective clouds.