The planets Mercury, Venus, Mars, Jupiter and Saturn can be seen without the help of a telescope, and, in the right conditions, it may also be possible to see Uranus without a telescope. It requires good eyesight, little light pollution and the knowledge of exactly where Uranus is in the night sky to see it, making it difficult or impossible to see without a telescope.
Mercury, Venus, Mars, Jupiter and Saturn are the five brightest planets and can be seen with the naked eye if a person knows where to look. These planets can be seen for much of the year, but it is rare to be able to see all of them in one night.
These five planets have been known since ancient times because of the differences people noticed between them and stars. Planets change positions when compared to stars from one night to another. Their brightness also changes on a cyclical basis over specific time periods. Stars, on the other hand, appear as points of light in the sky and, because of the Earth's atmosphere, appear to twinkle.
Uranus had been mapped as a star previous to its discovery in 1781. It was not discovered to be a planet until William Herschel spotted it with the help a telescope.