Page "Planet" Paragraph 2

The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions.

Although the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei.

By careful analysis of the observation data, Johannes Kepler found the planets ' orbits to be not circular, but elliptical.

As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons.

Since the dawn of the Space Age, close observation by probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology.