The ecliptic is the circular path of Earth's orbit around the Sun. During this movement classically 12 (actually 13) constellations that are in the background beyond the Sun are sequentially hidden from view by the Sun. These constellations comprise the Zodiac. They are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus, Sagittarius, Capricornus, Aquarius and Pisces. This line-up of constellations was recognized in ancient times. The early Greeks visualized animals moving among the constellations of the Zodiac. Each constellation is depicted as an animal except for Libra. 'Zodiac' means animal in Greek.
Since all of our planets except Pluto orbit the Sun close to the same orbital plane as Earth they are always seen close to the ecliptic and therefore along the Zodiac highway of 13 constellations. See Fig. 7.
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