Some astronomical bodies were observed by ancient astronomers to be changing their positions

While studying the sky, ancient astronomers observed that while most of the stars maintained fixed relative positions, there were a few heavenly bodies that obviously changed their positions in relation to each other and to the greater number of so-called fixed stars.

• The most obvious of these were the sun and the moon; but five others seemed to revolve around the Earth at different rates.
• These five (Mercury, Venus, Mars, Jupiter, and Saturn) were called by the Greeks asteres planetai (wandering stars) or planetai (wanderers).
• The Latin term used in place of the Greek was stellae errantes (wandering stars); but Late Latin borrowed the Greek term in the plural form, planetae, while the singular was planeta.
• By way of Old French, Middle English borrowed this word in the fourteenth century to give us the modern planet.
• Later, not only has the word become completely anglicized but three more planets were discovered: Uranus in the eighteenth century, Neptune in the nineteenth, and Pluto in the twentieth.

A medical term for "a tree struck by blight" comes from an old belief that malignant aspects of the planets caused death and suffering on earth. When plants and animals died or fell ill for no apparent reason, they were said to be planet-struck. The term is first recorded in 1600.

• The ancients were convinced that there were just seven planets including the: Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn.
• It was also strongly believed that these planets were particularly important in the affairs of mankind.
• The astrological study of their positions among the stars at the moment of one’s birth was supposed to give information about his/her fate.
• The general character of a person was thought to be determined by which planet she/he was “born under” according to the calculations of astrologers, and such superstitions continue in modern times.
• Each of the seven planets was also believed to have a special influence over its designated day of the week: First day, Sol or the Sun; Second day, Luna or the Moon; Third day, Mars; Fourth day, Mercury; Fifth day, Jupiter; Sixth day, Venus; and the Seventh day, Saturn.
• The alchemists of the Middle Ages noted that there were seven planets and seven metals which were matched with the planets.
• The seven metals presented by the alchemists and matched with the planets include (in English): gold (Sun), silver (Moon), copper (Venus), iron (Mars), tin (Jupiter), lead (Saturn), and quicksilver (Mercury).
• Much more has been learned about the planets since 1977 because of the flights of Voyagers 1 and 2 (you may see a summary of the subject with a simple click).

Planets with and without Moons in their Orbital Orders from the Sun

• Mercury, no moon
• Venus, no moon
• Earth, one moon: Moon (Luna)
• Mars, two moons: Phobos and Deimos
• Jupiter, sixteen moons: Metis, Adrastea, Amalthea, Thebe, Io, Europa, Ganymede, Callisto, Leda, Himalia, Lysithea, Elara, Ananke, Carme, Pasiphae, and Sinope
• Saturn, eighteen moons: Atlas, Prometheus, Pandora, Epimetheus, Janus, Mimas Enceladus, Tethys, Telesto, Calypso, Dione, Helene, Rhea, Titan, Hyperion, Lapetus, Phoebe, and Pan
• Uranus, fifteen moons: Cordelia, Ophelia, Bianca, Cessida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck, Miranda, Ariel, Umbriel, Titania, and Oberon
• Neptune, eight moons: Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, and Nereid
• Pluto, one moon: Charon

A cross reference of word units that are related, directly or indirectly, to the: "moon": Calendar, Moon Facts; Chemical Element: selenium; Gods and Goddesses; luna, luni-; Luna, the earth moon; menisc-; meno-; plano-; seleno-.