To be more specific, a sign usually occupies the time span from one month into another. During this time, planets move through the Sun sign adding certain qualities unique to that 10 day time period within the Sun sign. Your Decante does not change your Sun sign, it only adds certain qualities to it. This is why not all Virgo’s (as an example)are exactly the same (in conjunction with your own personal, individual birth chart). You may wonder, why is this Virgo much more outgoing than the other Virgo? They have a different set of underlying qualities.
Constellations rule each decante. Each constellation has special mystical traits that give each decante a “feel.” For instance, the Chained woman who governs over the first decante of Aries symbolizes the power of love. This could mean that people born between March 21 and March 31 will experience a special transformative effect from finding themselves in love, or in a relationship that builds them up, reaching their true potential. But because their sub-ruler is Mars, not Venus, you will also see a very courageous, outgoing, honorable personality traits accompanying the rest.
A decante literally means “10 days apart” and comes from the Egyptian calendar which divided each month into 10 days to correlate to the stars and the constellations.