The zodiacal constellations are found in a ring along the celestial equator, formed from the chance superposition of the stars which lie along these lines of sight. As the Earth rotates once around the Sun in a year, the Sun appears to pass through (or lie in front of) each of these constellations in turn. Its path is called the ecliptic. Because the Earth is tilted by 23 degrees with respect to its orbital plane, the ecliptic moves up and down between +23 and -23 degrees of the celestial equator. On the spring and fall equinoxes (March 21 and September 21), the two coincide.

The peak altitude of the Sun each day, as viewed from the northern hemisphere, increases by 23 degrees from March 21 until June 21 (the summer solstice). On this day the Sun is said to stand still in the sky, and then it turns around and heads back toward the celestial equator, crossing it again on September 21 and then descending further in the sky every day till December 21 (the winter solstice). On the solstices, the Sun lies directly overhead at noon at the Tropics of Cancer or Capricorn (23 degrees above and below the equator).

If you like to read the daily astrological horoscopes in the newspapers for yourself and your friends and family, you are probably familiar with the names of these constellations: Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Maiden), Libra (the Scale), Scorpio (the Scorpion), Sagittarius (the Archer), Capricorn (the Goat), Aquarius (the Water-Carrier), Pisces (the Fish), Aries (the Ram), and Taurus (the Bull).

The table shown below shows illustrations of the images behind the zodiacal constellations, and the months in which they will rise highest in the sky (transit) at midnight. A constellation which is overhead at midnight during a particular month will then lie behind the Sun six months later, because of the Earth's yearly motion around the Sun.

One might expect the birth dates associated with each constellation to match the dates on which the Sun lies within that constellation. A quick check, however, shows that Aquarius (the astrological sign for those born between January 20 and February 18) lies behind the Sun in early March, not February, and that the other dates are off as well. This mismatch occurs because over time the precession of the equinoxes, due to a wobble in the orientation of the Earth's rotational axis, has shifted the timing between the seasons and the constellations. As the Earth's rotational axis shifts slightly, it can take a few minutes extra for spring, and each of the other seasons, to arrive, because they depend on the Earth pointing exactly toward, away, or perpendicular to the direction to the Sun. Over thousands of years those few minutes can add up, leading to delays of weeks or even months. The same factor will slowly shift our rotational axis toward and away from Polaris over time, leading to new contenders for the title of North Star.

Gemini	Cancer	Leo	Virgo	Libra	Scorpio
January	February	March	April	May	June
Sagittarius	Capricorn	Aquarius	Pisces	Aries	Taurus
July	August	September	October	November	December
Fifteenth century representations of the zodiacal constellations illustrate the western mythology behind them. The months listed indicate the current times of the year at which they will appear highest in the sky at midnight.