The Western tradition divides the twelve signs into two alternating groups, beginning with Aries. Ptolemy treats them in the first book under the heading of masculine and feminine signs, and the division is mechanical: Aries belongs to the first group, Taurus to the second, and so on round the circle without exception.
The result is that the six fire and air signs form one group and the six earth and water signs the other. Aries, Gemini, Leo, Libra, Sagittarius and Aquarius are the active, projective, outward group this entry records as yang. They are the diurnal or masculine signs in the classical terminology, and the two elements they comprise, fire and air, are the two the classical physics counts as light and rising.
The property matters chiefly through the planets. A planet in a sign of its own charge is at ease in a way the tradition notices, and the doctrine of sect, which sorts the planets into a day team and a night team, runs on the same underlying distinction. Ptolemy classifies the planets themselves as masculine or feminine as well, so a full reading of any placement weighs the charge of the planet, the charge of the sign and the sect of the chart together.
The alternation is one of the small number of structural facts about the zodiac that no branch of the Western tradition disputes.
Sources TetrabiblosClaudius Ptolemy with A History of Western AstrologyNicholas Campion