Planet
An ancient Greek term meaning wandering star - as opposed to the backdrop of the fixed stars.
This term has different meanings in astronomy and astrology.
Astronomy
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The two meanings started diverging after the Copernican revolution, when the Sun was put at the center of our solar system and the term planet started indicating a celestial body orbiting directly the Sun; planets reflect the Sun's light - rather than being luminous themselves - and circle it along elliptical orbits. Their orbital period is determined by their distance from the Sun: the further away they are, the longer their orbital period.
Numerous new celestial bodies have been discovered in our solar system since the beginning of the 19th century (asteroids, centaurs, the Kuiper Belt and many new discoveries can be expected in the future), but very few added to the count of known planets, the others being classified as either minor planets or comets.
Up to 2006 astronomers counted nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
Only Mercury, Venus, Mars, Jupiter and Saturn are visible from the Earth with the naked eye, which is why they caught the attention of ancient cultures (see History of Astrology). Uranus, Neptune and Pluto were only discovered fairly recently with the aid of technology (telescopes).
- Mercury and Venus are classified as inner planets because they orbit the Sun within the Earth's own orbit.
- Mars, Jupiter and Saturn are classified as outer planets with orbits outside of the Earth's.
- Mercury, Venus, Earth and Mars are similar in structure and size; Jupiter, Saturn, Uranus and Neptune are classified as giant planets.
- Pluto is the only ice planet.
Mercury, Venus and Mars all have smaller masses than the Earth, and the giant planets all have considerably larger masses. Jupiter's mass is 318 times that of the Earth, and Saturn's is 95 times as large. Pluto has the smallest mass of all nine planets. All planets apart from Mercury and Venus have at least one moon.
In 2006 the International Astronomical Union (IAU) introduced a new definition of planet, as a celestial body orbiting the Sun that is large enough to be "round" and that does not share its orbit with other celestial bodies of comparable size. This definition does not hold for Pluto, that has been reclassified as a dwarf planet. Thus the count of known planets in our solar system is currently eight.
Astrology
Astrology classifies the planets in a different way to astronomy because the focus is different. The planets are seen from the Earth perspective and the classical definition of wandering star is kept.
The Sun and the Moon are counted as planets but the Earth is not included because it is the location of the observer - and also horoscope owner. Therefore, the seven classical planets in astrology are: Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn (see Number Mysticism). Since the discovery of Uranus, Neptune and Pluto most astrologers have worked with ten planets.
These planets are divided into three groups - personal, social and spiritual planets: the latter are Uranus, Neptune and Pluto, the social planets are Jupiter and Saturn and the five remaining planets are classified as personal planets.
Some other celestial bodies are also included in some astrologers' works: the asteroids Ceres, Pallas, Juno and Vesta and the centaur Chiron enjoy increasing popularity. Astronomic classification does not affect astrology, so these objects are to be counted as planets as long as their perceptible attendance is considered. This also holds for Pluto: its astrologic importance is not affected by its astronomical reclassification, therefore it is to be counted as a planet.
All the planets except the Sun and the Moon are named after gods of antiquity. Astrology attaches significance to the myths associated with these gods. Of the seven classical planets the Moon, Venus and Saturn were considered to be feminine, the Sun, Mars and Jupiter masculine and Mercury hermaphroditic.
The planets, zodiac sign and houses form the basis for most astrological interpretation. The planets represent archetypal energies in humans which are additionally coloured by their position in the signs. The house position indicates the area of life in which these energies will be expressed.
There is disagreement among astrologers about which model best explains the way astrology works - whether the planets have some kind of direct physical influence (Causality) or whether they are only indicators (in the way that the hands of a clock indicate the time without actually causing it) (Analogy).
The following table gives a quick summary of the meaning of each planet (more details can be found under the headings of individual planets):
- Sun: Life energy, will, spirit
- Moon: Emotions, ability to conceive, body
- Mercury: Thought, communication
- Venus: Aesthetic sense, self-esteem
- Mars: Self-assertion, will to achieve
- Jupiter: Expansion, principle that gives meaning
- Saturn: Concentration, principle that sets limits
- Uranus: principle that breaks with limits
- Neptune: principle that dissolves limits
- Pluto: Transformation
