Western astrology originated in Mesopotamia during the 2nd millennium BC, from whence it spread to much of the world. Other systems of astrology were developed independently in China, in the Americas and elsewhere. Premodern observers noticed that the annual patterns of the movement of the stars coincided with such events as the advent of springtime, changes in weather and the migration of birds every year. Without knowing why these phenomena occurred together, other events were said to be affected by the stars as well. In medieval Europe, important political and military decisions were often made in consultation with astrologers. Today, believers in astrology use it primarily for making personal decisions, and astrology has become distinct from astronomy. Mainstream scientists in general dismiss astrology as a form of pseudoscience.

Astrological charts or horoscopes based on a person's birth will show where the stars and planets were in relation to each other at the moment of birth, and the person's specific latitude and longitude at that time. The most prominent of these features is the position of the sun in relation to the signs of the zodiac. From these planetary positions astrologers draw certain conclusions about the person. Similarly, a horoscope may be prepared to reflect circumstances of an event.

Newspapers often print astrology columns, which purport to provide guidance on what challenges might be found in a day, as determined by where planets and stars are on that day, in relation to the sign of the zodiac that included the sun when the person was born. Professional astrologers refer to this as the "sun sign", but it is often incorrectly called the "star sign" in newspapers. Typically these predictions, an innovation of 20th century newspapers, are vague or general, so that even practising astrologers consider them useless. People presented with randomly-chosen newspaper column report the same degree of accuracy as those given specifically prepared ones. Professional astrologers claim that a more complete, personalized chart is more effective, but critics claim that this is not the case (see external link to "The AstroTest" below).

There are two camps of thought among astrologers about the "starting point", 0 degrees Aries, in the Zodiac. Sidereal Astrology accepts that the starting point is at a particular fixed position in the background of stars, while Tropical Astrology (which is adopted by most astrologers) accepts that the starting point is the position in the background of stars where the Sun appears in the sky at the vernal equinox (when the Sun appears to cross over from the southern hemisphere to the northern hemisphere) each year.

As the Earth spins on its axis, it "wobbles" like a top, causing the vernal equinox to move gradually backwards against the star background, (a phenomenon known as the Precession of the equinoxes) at a rate of about 30 degrees (one Zodiacal sign length) every 2160 years. Thus the two Zodiacs are aligned only once every 26,000 years, with the most recent alignment being about 2000 years ago when the zodiac was principally established. This phenomenon gives us the conceptual basis for the Age of Aquarius, whose "dawning" coincides with the movement of the vernal equinox across the cusp from Pisces to Aquarius in the star background.

Astrological symbols (most of these will not display correctly in many browsers):

• ☄ - Comet
• ☉ - Sun
• ☊ - Ascending Node
• ☋ - Descending Node
• ☌ - Conjunction
• ☍ - Opposition
• ☽ - First Quarter Moon
• ☾ - Last Quarter Moon

• ☿ - Mercury
• ♀ - Venus (Female Sign)
• ♁ or ⊕ - Earth
• ♂ - Mars (Male Sign)
• ♃ - Jupiter
• ♄ - Saturn
• ♅ - Uranus
• ♆ - Neptune
• ♇ - Pluto
• ♈ - Aries
• ♉ - Taurus
• ♊ - Gemini
• ♋ - Cancer
• ♌ - Leo
• ♍ - Virgo
• ♎ - Libra
• ♏ - Scorpius
• ♐ - Sagittarius
• ♑ - Capricorn
• ♒ - Aquarius
• ♓ - Pisces

See also: How to cast a horoscope

External links

• American Federation of Astrologers
• Astrology and Science - A series of articles in which believers and skeptics debate the merits of astrology.
• The Astrotest - An account of a test of the predictive power of astrology, with references to other experiments.