* Ancient people knew about: Mercury, Venus, Mars, Jupiter, and Saturn. These were visible to the naked eye and were considered "wandering stars" because they moved against the backdrop of the fixed stars.

* Planets discovered later:

* Uranus: Discovered in 1781 by William Herschel.

* Neptune: Discovered in 1846 through mathematical predictions and observations.

* Pluto: Discovered in 1930 by Clyde Tombaugh. While Pluto was initially classified as a planet, it was reclassified as a dwarf planet in 2006.

So, the 3 planets not known to ancient people are:

1. Uranus

2. Neptune

3. Pluto (though technically now a dwarf planet)