12 zodiac signs and constellations: what's the difference

Zodiac signs are the most popular words in horoscopes, but they are also the source of the most misunderstandings. "There are 12 signs and 13 constellations on the ecliptic", "Ophiuchus cancels Scorpio", "the dates of the signs don't match the constellations" — let's figure out where the truth lies.

Signs of the zodiac are sectors, not constellations

The key difference: a sign is a mathematical sector of 30°, and a constellation is a real region of the sky. The entire ecliptic circle of 360° is divided into exactly 12 parts. Each part bears the name of one of the zodiacal constellations, because those constellations lie along the path of the Sun.

Constellations, in turn, have irregular shapes and different areas. One constellation can occupy 50°, another only 10°. That is why there is no exact correspondence of "one sign = one constellation".

Twelve signs and thirteen constellations

Modern astronomy divides the sky into 88 constellations. Thirteen of them cross the ecliptic:

• Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Ophiuchus, Sagittarius, Capricorn, Aquarius, Pisces.

The tropical scheme does not take Ophiuchus into account: there are exactly 12 signs. In the astronomical system the boundaries follow the standard of the International Astronomical Union, and there the dates when the Sun is "in a constellation" really reflect the position of the star. That is why the astronomical calendar sometimes does not match the classic horoscope.

When the Sun "enters" a sign — by sectors

In the tropical zodiac the boundaries of the signs are fixed. The table of the most common dates:

These dates "float" by 1–2 days in different years.

In the sidereal zodiac the same dates shift by about 24° (the ayanamsa): a sign that was Aries in the tropical system will be Pisces in the sidereal system. In the astronomical system the dates are not divided into signs at all — it simply states in which constellation the Sun actually is.

Seven planets + the Sun and Moon pass through each sign

The Sun is not the only one that "wanders" through the signs. An important point for the lunar calendar: the Moon passes the whole belt in about 27–28 days, spending about 2.3 days in each sign. That's why "the Moon in Taurus" changes every two or three days. Planets pass through signs over months or years — from Mercury (a few days) to Pluto (years).

Boundaries between systems

• Tropical zodiac: 12 signs, tied to the equinox, dates as in the table.
• Sidereal zodiac: 12 signs, tied to the stars, shifted by the ayanamsa.
• Astronomical zodiac: 13 segments according to the actual coordinates of the constellations.

Summary

There are 12 signs and 13 constellations on the ecliptic, and that is not a mistake. Signs are equal sectors created for convenient calculations; constellations are real areas of the sky. The dates of "entering" a sign depend on the chosen system. On lunar.day you can see the tropical, sidereal, and astronomical boundaries together — and always understand where in the zodiac belt the Moon is at that moment.

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See also: what the zodiac is, types of zodiac systems.