On first viewing Mars through a telescope, beginners are struck by how small it appears.| The planet is only half the of Earth and, even at favorable oppositions, it appears no larger than a lunar crater. views typically show an disk, a few faint markings, perhaps a whitish polar cap. The most powerful telescopes on Earth give views of Mars only about as detailed as naked-eye views of the Moon.
This helps explain why Martian studies progressed little before the Space Age.
Early observers of Mars saw dark markings and thought they were either old seabeds or areas of vegetation. Today, these are known to be lava flows and boulder fields.
In 1877, the Italian astronomer Giovanni Schiaparelli reported seeing a network of straight lines he called canali, meaning channels. This was widely translated as canals, suggesting these features were artificial and fueling popular speculations about life on Mars. As it turned out, the canals were merely optical illusions.
In 1964, the first close-up views of Mars were taken by NASA's Mariner 4 spacecraft. The features in these photos that most shocked scientists and the public alike were the craters—very few people had expected to see such Moon-like features. The fact that a Moon-like Mars was such a shock reveals the depth of most people's assumptions that Mars was just a "little Earth."