| Home | Articles | Guide to Observing | Tour of the Constellations | Book Reviews |
The four innermost planets of the Solar System are called the terrestrial planets. These planets - Mercury, Venus, Earth and Mars – are all to some slight degree Earth-like in that they have very roughly the same size and are solid.
Already thousands of years ago, it was noticed that certain "stars" were not fixed. Over a period weeks and months they would wander back and forth along roughly the same path as the Moon and Sun – the ecliptic, and were appropriately called planets, from the Greek word for "wanderers". These five bright, restless stars were named Mercury, Venus, mars, Jupiter and Saturn.