Mercury, Venus, Mars, Jupiter and Saturn are the five planets that are visible without a telescope. These five planets were known to ancient astronomers long before the invention of telescopes. Some experts also include the Earth on the list of planets you can see with the naked eye.
The planet Venus was at one time the most volcanically active planet in the solar system. Its surface is strewn with both large and small volcanoes, and some of the volcanic processes that seem to have occurred on the planet are unlike any known on Earth.