The Beginning of the Signs Is Decided by the Vernal Equinox Day
The 12 signs of Western astrology use a way of counting that makes the position the Sun enters on the vernal equinox day the beginning of Aries. This system is called the tropical system.
The vernal equinox is one of the seasonal break points. Because the Sun's position is counted in connection with the seasons, in this system the correspondence between signs and seasons is fixed. The correspondence that Aries is the period of the beginning of spring is decided not from the arrangement of the stars, but from the convention of this way of counting.
In 2027, by calculation, the Sun enters Aries on March 21. This day is the beginning of the Aries period for that year. The form where the beginning of spring and the beginning of Aries overlap repeats in the same way every year as long as the tropical system is used.
What It Means to Be Connected with the Seasons
Signs in the tropical system are connected with the seasons. If you look at which sign the Sun is in, you can tell where that period is within the seasonal flow of one year.
This connection also affects readings. In content spoken of as the nature of signs in fortune-telling, there are parts that overlap with seasonal impressions. A view can be taken that the seasonal flow — a period of beginning, a period of fruitfulness, a period of organizing — is one foundation for how signs are read.
Conversely, sign periods do not shift from the seasons in this system. Even if the day a period begins shifts by about one day by year, the correspondence with the seasons themselves is preserved. Being able to use signs as seasonal markers is a characteristic of this system.
It Has Shifted Little by Little from Astronomical Constellations
On the other hand, the signs of the tropical system have shifted from what are called constellations in astronomy — that is, constellations based on the actual arrangement of stars.
The reason for the shift is Earth's precession. Because of a movement where the axis of Earth's rotation changes direction little by little over a long time, the direction in which the Sun is seen on the vernal equinox day also moves little by little over long years. Because the tropical system fixes the vernal equinox position as the beginning of Aries, a difference widens between it and the actual arrangement of stars as time advances.
For that reason, during the Aries period as spoken of in fortune-telling, the Sun is not necessarily in the direction of Aries in the actual arrangement of stars. Both use the same name "Aries," but their starting points for counting are different.
This shift is not a matter of deciding which is correct. Astronomy handles the actual arrangement of stars, and astrology is established on a convention that takes the vernal equinox as its starting point. It is accurate to understand that two ways of counting with different starting points exist side by side.
How to Look When Reading Period Tables
If you know this system, how you read sign period tables also changes. The beginning of a period is not the day the arrangement of stars switches, but the day the Sun's position, counted from that year's vernal equinox as the starting point, moves to the next sign. For that reason, even if the starting day shifts by about one day by year, the correspondence with the seasons itself does not change.
Also, not only the Sun's periods, but also the sign changes of other planets are counted on the same tropical circle. The planetary movements listed in this site's monthly horoscope are all calculated aligned in this one system. Precisely because the system is aligned, you can compare the positions of multiple planets within the same table. When reading a table, please look at it not as a map of the actual starry sky, but as positions on a seasonal circle with the vernal equinox as its starting point. If that premise is understood, you will not misunderstand the meaning of dates.
The Meaning of Knowing It as a Convention
If you know this mechanism, how you associate with fortune-telling readings becomes clear.
Expressions written in monthly horoscopes and articles such as "the Sun moves into Aries" refer to movement within the tropical system. The dates listed as the basis are also calculated based on this system. If you read knowing that it is a system separate from observation of the actual starry sky, you will not mistake the meaning of expressions.
Also, on the fortune-telling side as well, there are schools that use a way of counting aligned with astronomical constellations, but this site uses the tropical system. The fact that the system is made explicit also means that the premise of the reading is clear. Deciding for yourself, after knowing the premise, whether to use it is a way of associating with fortune-telling without strain.
When using signs for organizing work and daily life as well, this premise does not change. A reading that uses them as break points connected with the seasons is something that is established precisely because it is the tropical system. A usage such as being conscious of March 21, the vernal equinox, as one break point in the flow of the year overlaps without strain with a seasonal sense as well.
The 12 signs are not the arrangement of stars in the sky itself. They are a convention that divides the seasons into 12 with the vernal equinox as the starting point. Knowing that convention becomes the foundation for correctly understanding articles.