If you read a horoscope in September, you were told that the Sun entered Libra on September 23. Yet on that day, and for the five weeks that followed, the Sun was in front of the stars of Virgo. In 2026 the Sun enters the constellation of Libra on October 31 and leaves it on November 23. Why is there such a difference?
Two different zodiacs
Western (tropical) astrology measures the zodiac from the vernal equinox, the point where the Sun crosses the celestial equator in March. From that point it divides the sky into twelve equal parts of 30 degrees, and gives each part the name of a sign. The stars play no role in this system.
Astronomy looks at the real sky. The zodiac constellations are patterns of stars of very different sizes, and the Sun needs a different number of days to cross each one. Libra is a small constellation: the section of the ecliptic that it contains has an arc of only 23.2 degrees, so the Sun passes through it in about 23 days instead of 30.
The wobble of the Earth
The Earth's axis moves like the axis of a spinning top. This slow motion, called the precession of the equinoxes, completes a cycle in about 25,920 years. As a result, the equinox points slide backwards along the ecliptic, about one degree every 72 years.
When the Hellenistic astronomers, whose principles Western astrology still follows, fixed the signs, the spring equinox lay near the beginning of the zodiac. Today the sky has shifted by roughly 29 degrees. The autumn equinox, which in antiquity lay in Libra, now falls in the constellation of Virgo.
The Sun's path this autumn
| Sign | Western astrology | 13 Signs (2026) |
|---|---|---|
| Virgo | Aug 24 – Sep 22 | Sep 17 – Oct 31 |
| Libra | Sep 23 – Oct 23 | Oct 31 – Nov 23 |
| Scorpio | Oct 24 – Nov 22 | Nov 23 – Nov 30 |
| Ophiuchus | – | Nov 30 – Dec 18 |
| Sagittarius | Nov 23 – Dec 21 | Dec 18 – Jan 20 |
Notice how short Scorpio is: the Sun stays there for only about a week before entering Ophiuchus, the thirteenth sign that Western astrology leaves out.
A sign with a long history
Libra was not always a separate constellation. The ancients called it Chelae Scorpionis, the claws of the Scorpion. It took the name Libra, the Scales, in the age of Hipparchus, in the 2nd century B.C. It is the only zodiac sign represented by an inanimate object, and its name comes from its old position on the ecliptic, when it divided the sky in half.
What does this mean for you?
If you were born between October 31 and November 23, the Sun was in the stars of Libra when you were born. If your birthday falls in October, it is likely that you are a Virgo in the real sky. The exact dates change slightly from year to year, so check the tables for the year closest to your date of birth.
You can find these tables, together with the characteristics of all 13 signs, in my book Astrology of the 13 Signs of the Zodiac.