Neptune Is the Only Planet You Cannot See With the Naked Eye

Several planets can be seen in the night sky without a telescope. Neptune is the exception. NASA states that Neptune is the only planet in our solar system not visible to the naked eye. The reason is distance. Neptune is more than 30 times as far from the Sun as Earth, far enough that, in NASA’s words, high noon on the planet would seem like dim twilight to us. That distance also makes for a very long year. Neptune takes about 165 Earth years to complete one orbit of the Sun. It was discovered in 1846, and NASA notes that in 2011 it completed its first full orbit since that discovery.