Zodiac constellations are constellations that lie along the plane of the ecliptic.
The ecliptic, or the apparent path of the Sun, is defined by the circular path of the Sun across the sky, as seen from Earth. In other words, the Sun appears to pass through these constellations over the course of a year.
The passage of the Sun through the zodiac is a cycle that was used by ancient cultures to determine the time of year. Most of the planets in the solar system have orbits that take them near the ecliptic plane, within about 8 degrees above or below.
The northern zodiac constellations – Pisces, Aries, Taurus, Gemini, Cancer and Leo – are located in the eastern celestial hemisphere, while the southern – Virgo, Libra, Scorpius, Sagittarius, Capricornus and Aquarius – are found in the west.
The word zodiac comes from the Greek ζῳδιακός (zōidiakos), meaning the “circle of animals.” The Latin term zōdiacus was derived from the Greek, and the Greek term comes from the word ζῴδιον (zōdion), which is the diminutive of ζῷον (zōon), or animal. Seven of the constellations found along the ecliptic represent animals, as they did in Greek and Roman times: Aries (the Ram), Taurus (the Bull), Cancer (the Crab), Leo (the Lion), Scorpius (the Scorpion), Capricornus (the Goat), and Pisces (the Fish).
Today, the term zodiac is mostly associated with astrology, with the 12 signs of the western zodiac corresponding to the 12 constellations seen along the ecliptic. The so-called cardinal signs (Aries, Cancer, Libra and Capricorn) mark the beginning of the four seasons, i.e. the Sun is said to enter these signs on the first days of spring, summer, autumn and winter respectively.
The largest of the 12 zodiac constellations is Virgo, which covers 1294.43 square degrees of the southern sky. Virgo is also the second largest of all 88 constellations, only slightly smaller than Hydra.
Covering an area of 979.85 square degrees, Aquarius is the second largest zodiac constellation and the 10th largest constellation in the sky. Also located in the southern celestial hemisphere, Aquarius represents Ganymede, the cup bearer to the Olympian gods in Greek mythology.
Leo, the third largest zodiac constellation, occupies an area of 946.96 square degrees of the northern sky. It represents the Nemean lion, a mythical monster killed by Heracles as part of his 12 labours.
Pisces comes in 4th with 889.417 square degrees, followed by Sagittarius (867.43 square degrees) and Taurus (797.25 square degrees). Libra (538.05), Gemini (513.76), Cancer (505.87) and Scorpius (496.78) cover areas similar in size and on the smaller end of the scale Aries occupies an area of 441.39 square degrees while Capricornus, the smallest of the 12 zodiac constellations, covers 413.95 square degrees of the southern sky.
In terms of brightness, several of the 12 constellations contain some of the brightest stars in the sky. Aldebaran, the brightest star in Taurus, is the 14th brightest of all stars, followed by Spica, the brightest star in Virgo and 15th brightest star in the sky, Antares, the bright red supergiant in Scorpius and 16th brightest star, Pollux in Gemini, the 17th brightest of all stars, and Regulus in Leo, which comes in 21st overall.
Today, zodiac constellations are most commonly brought up in the context of western astrology, as the 12 constellations correspond to the 12 signs of the zodiac.
The problem with linking the astronomical constellations with astrology to give the latter a more “scientific” foundation is a simple one: the constellations themselves aren’t real. They are groups of stars that appear to be close to each other, arbitrarily named after different objects, animals, or figures from mythology by human observers at some point in history.
Constellations make a two-dimensional map of the sky used for orientation, to make it easier for astronomers to find objects and explain their location and for navigators to use stars to determine their position. The universe itself, on the other hand, isn’t flat and doesn’t revolve around our planet, which is what makes these groupings of stars arbitrary. While even Carl Gustav Jung said that astrology holds some value as a theory of the personality, and it can use the scientific approach, it is in itself not based on any kind of science.