Sun signs and seasonal effects

Hamilton M (2015) and seasonal effects

Mark Hamilton is a psychologist who published a paper discussing the validity of a study by Adel MM et al (2013) assessing the correlation between sun signs and the achievement of fame in 100 celebrities, which drew the conclusion that a significantly higher number of celebrities were born with their sun in Aquarius. The study had been subject to a number of criticisms, which Hamilton addresses, coming to the conclusion that they carry little weight and that an effect of the sun signs was indeed documented.
He also discusses potential mechanisms whereby the sun signs might exert this effect and comes to the conclusion that “The interlocutors in this exchange would surely agree that distant star clusters do not exert mystical effects on earthly events. Whether they agree on the mediating role of seasonal birth heuristics is harder to foresee”.
In other words, he suggests that the correlation between the sun signs and certain features of people are related not to strange forces emitted from distant stars, but rather to seasonal effects.
He argues that the sun signs were originally used as sign-posts for the seasons. Once upon a time information on the seasons i.e. on when to start planting, how long winter would last etc. was essential for survival. Clusters of stars were given particular names and were related to mythical stories featuring particular characteristics so that the illiterate population would remember them easily and would pass these stories on, together with key information on seasons, to the next generations. Indeed, if you come to think of it, the sign of generous and warm Leo reflects the features of the strong sun in summer, whereas the cold and reserved sign of Capricorn reflects winter.
But how can the seasons affect the personality of people?

Tendler et al (2021) and seasonality in hormone production

Israeli researchers analyzed electronic medical record data from a large Israeli health
service organization, which includes millions of blood tests, correcting for circadian effects due to the time of day. The dataset included measurements from about half of the Israeli population over 15 y (2002−2017), with broad socioeconomic and ethnic representation. They observed a clear seasonal pattern in hormone product, with peak levels of hormones for reproduction, growth, metabolism and stress adaptation in the winter−spring period. Also the levels of certain substances in the bloodstream, such as glucose and electrolytes, showed seasonal oscillations

Hormone seasonality as a potential explanation for the correlation of personality traits and sun signs

The findings of the Israeli researchers imply that the unborn child is exposed to different maternal hormonal levels according to the month of conception, which may result in qualitative differences in the development of the central nervous system. It is understood that the differences in development would vary also according to the genetic features of the unborn child.
Before you dismiss this potential explanation, just think of the well-known side effects that the corticosteroid hormones (i.e. cortisone ….) can have on human beings taking them for therapeutic purposes after only a few weeks (increase in blood pressure and blood sugar, change in fat distribution and mood, reduction in muscle mass and skin thickness …).

Precession of the equinoxes

The interpretation of the sun sign effects as seasonal effects addresses the issue of precession ofthe equinoxes (= days when daytime and night-time have the same duration).  Astronomers have unequivocally shown that the Earth wobbles on its axis so that the axis progressively points in a different direction in space i.e. that the North pole gradually changes the fixed stars it points towards.  This results at the same time in a progressive shift in the sign in which the sun appears to be in at the equinoxes.  The wobble occurs as a very slow cycle and the Earth’s axis returns to its original position approx. every 26,000 years.  Since the zodiac has 12 signs, their position changes approximately every 2,000 years.  The wobble is illustrated below.

The problem raised by the adversaries of astrology is that astrology texts still bear the same dates for the sun signs as they did 2,000 years ago. From an astronomical perspective, people who are said to have their sun in Leo, no longer do, because Cancer is currently there and Cancer will soon be replaced by Gemini.
However, if the sun sign is considered only as a sign-post for the season with its effects related to the change in climate, rather than a star cluster emitting strange, unknown effects then the precession has no impact, since the seasons have not changed.