A constellation is a group of stars joined by imagination into a figure: a lion, a pair of scales, twins.
The current boundaries, drawn in 1930 under the auspices of the International Astronomical Union, divide the whole sky into 88 regions of very different sizes. Along the Sun’s path, Virgo stretches wide while Cancer is compact.
A sign is something else: a division of the ecliptic into twelve equal parts of 30 degrees, counted from a starting point. The sign is a measure of position, not a figure in the sky. It depends on no particular star, and a circle cut into twelve equal parts lends itself to a simple calculation, with no exceptions.
The two long coincided, hence the shared names. The precession of the equinoxes shifted them, until a tropical sign today mostly overlaps the previous constellation. This distinction explains two common questions: why Ophiuchus is not a sign, and why the sidereal zodiac gives a different result from the tropical. It also reminds us that a shared name does not guarantee the same reality: reading “Aries” in a chart means reading a portion of the ecliptic, not looking at the constellation.
Family
The sky and the zodiac
The diagram
The Sun in the constellations
Read next
Ophiuchus, the “13th sign”
History, debates, and sources
A little history
Mesopotamian astronomers already picked out figures along the path of the Sun and the Moon, then divided that path into equal sectors, a practice passed on to the Greeks.
Ptolemy, in the 2nd century, holds both registers: the Almagest catalogs 1,022 stars grouped into 48 constellations, while the Tetrabiblos treats the signs as 30-degree sectors, measured from the equinox. The gap between the two widened afterward, without the names changing.
Sources
3
Oldest
Claudius Ptolemy, 2nd century
Most recent
Eugène Delporte, 1930
What is debated
Tropical schools hold the signs to be sectors measured by the Sun and the seasons, and the constellations to be visual landmarks with no other role.
Sidereal schools keep equal signs but tie them to the stars. A few authors would like to follow the actual boundaries of the constellations, which would give signs of very unequal lengths. All three positions still coexist.
Schools do not all agree: the site sets out the positions without deciding for you, and states the setting it uses by default.
Where this concept comes from
The authors and texts that establish or discuss this concept, with the passage when it is known.
2nd centuryClaudius PtolemyAlmagest, Books VII and VIII
Catalog of 1,022 stars grouped into 48 constellations.
2nd centuryClaudius PtolemyTetrabiblos, Book I
The signs are equal 30° sectors counted from the equinox, distinct from star patterns.
1930Eugène Delporte (International Astronomical Union)Délimitation scientifique des constellations, boundary tables
Official constellation boundaries, of very unequal sizes.
The diagram’s figures are calculated by the site’s engine (Astronomy Engine) or taken from the recorded facts, never copied by hand.
The Sun in the constellations
Sagittarius32 dDec 19 – Jan 19
Capricornus28 dJan 20 – Feb 16
Aquarius24 dFeb 17 – Mar 12
Pisces37 dMar 13 – Apr 18
Aries26 dApr 19 – May 14
Taurus38 dMay 15 – Jun 21
Gemini29 dJun 22 – Jul 20
Cancer21 dJul 21 – Aug 10
Leo37 dAug 11 – Sep 16
Virgo45 dSep 17 – Oct 31
Libra23 dNov 1 – Nov 23
Scorpius6 dNov 24 – Nov 29
Ophiuchus19 dNov 30 – Dec 18
The Sun in the constellations in 2026 (boundaries of the International Astronomical Union, calculated by the site): stays from 6 to 45 days, while each sign spans 30° (about 30 days).
Frequently asked questions: constellations and signs
Is a sign the same as a constellation?
No. A sign is a 30-degree sector of the ecliptic; a constellation is a pattern of stars with irregular boundaries. They share names because they overlapped more than twenty centuries ago, which is no longer the case since the precession of the equinoxes.
Why aren’t all constellations the same size?
Because they come from figures drawn by ancient peoples, not from a regular division. Their boundaries were drawn in 1930 around those figures. The Sun thus crosses Virgo in 45 days in 2026, and Scorpius in six.
How many constellations lie on the ecliptic?
Thirteen are crossed by the Sun’s path: the twelve of the zodiac and Ophiuchus. In all, the International Astronomical Union recognizes 88 for the whole sky. Only twelve carry an astrological sign, because of the division into equal sectors.