I’m mostly interested in astrology from an archetypal perspective. I think the jury is still out on the evidence
, but there has been some research done. The Wikipedia article on Solar Cycle
mentions three scientific fields that study the sun’s effect on life: Chronobiology
, and Astrobiology
. Obviously, the solar cycle influences us quite a bit such as with Season Affective Disorder, but the complication for astrology is that the seasons are opposite for Earth’s hemispheres. So, why should there be the same effect for someone born in winter as for someone born in summer on the other side of the planet?
There are an interesting relationships between solar cycles and planetary cycles, and there are many other solar cycles besides the daily and yearly cycles. Here is a site that shows the correlations between 11 year sun spot cycle and human activity. Here is a paper from a medical journal looking at various causes of moodiness including solar and lunar cycles. Here is a review of a book about astrology written by an astrophycisist (Dr. Percy Seymour). The reviewer quoted the author describing a theory of how astrology could be explained:
[P.263]“It is now accepted by almost all scientists that the sunspot cycle effects the magnetic field of Earth, and the agency responsible for this effect, the solar wind, has been detected. It is also beyond doubt that the moon causes tides in the upper atmosphere which give rise to electric currents, and these generate the lunar daily magnetic variation. There is also plenty of evidence that both the steady state as well as the fluctuating behavior of the geomagnetic field can be used by organisms, including man, for purposes of finding direction and keeping internal body time. This much is all well documented, and widely accepted.
There is evidence, largely ignored, that positions and movements of planets as seen from the sun, play a major role in the solar cycle. Furthermore, there is some evidence – highly controversial but difficult to dismiss – that some positions of the planets as seen from Earth at time of birth and linked to personality characteristics of individuals. [Gauquelin]
This evidence exists. What my theory does is to prepare an interpretation, based on this evidence, which can be scientifically tested. Very briefly the steps are:
(1) Planets effect the solar cycle in specific ways.
(2) The solar cycle effects the geomagnetic field.
(3) The geomagnetic field affects life on Earth in certain observed ways.
(4) Specifically, many species, including man, can be influenced by particular states of the geomagnetic field.
(5) The particular influences appear to correlate with the planetary positions.
(6) I propose that the behavior of the fetus at the time of birth is linked to the cycles
within the geomagnetic field, which in turn are influenced by the solar cycle and positions of the planets. Resonance is the phenomenon by which the fetus is phase locked to specific cycles.
To put this in more specific terms, my theory proposes that the planets Jupiter, Saturn, Uranus and Neptune control the direction of the convective motions within the Sun, which generate the solar magnetic field. They do so because they play the major role in moving the sun about the common center of mass of the solar system. As the solar cycle builds up to a maximum, so certain configurations of all the planets, at different stages, play a part in the disrupting the magnetic field of the sun, by means of the tidal tug (due to gravitation) of the planets on the hot gases in the Sun.
Thus the planets play a role in the modulation of Earth’s magnetic field by the solar wind. I am also proposing that the tidal tug of the planets on the hot gases trapped within our magnetosphere will, because of resonance, lock some of the vibrations of the Earth’s field in step with the planetary movements. The resulting fluctuations of Earth’s field are picked up by the nervous system of the fetus, which acts like an antenna, and these synchronize the internal biological clocks of the fetus which control the moment of birth. The tuning of the fetal magnetic antenna is carried on by the genes which it inherits, and these to some extent will determine its basic genetically inherited personality characteristics. Thus the positions of the planets at birth are not altering what we have inherited genetically but are labeling our basic inherited personality characteristics.”
The reviewer also quotes the author’s opinion about Michel Gauquelin:
“Battling with heroic courage and tenacity against the immense scientific prejudice and hostility of his colleagues in the scientific community, he was able to conclusively demonstrate, through repeated and stringently controlled experiments, that, as the ancients had believed, outstanding individuals in different professions tend to be born at times when appropriate planets were close to the horizon or the meridian.
He was able to show that top military men, athletes, and entrepreneurs tend to be born “under Mars”, while scientists favor Saturn, poets and politicians favor the Moon, and actors Jupiter. He was able to show that the more outstanding the individual the more likely appropriate planets would be prominent. He went on to demonstrate that, in the case of natural births, children tend to be born with the same planets prominent in the sky at birth as their parents.”
Michel Gauquelin’s research on the Mar’s effect came up in the commentary of one blog here on Gaia. Julian blogged about the forer effect in astrology (here), and the discussion that followed was fairly interesting.
A while back, I looked into lunar cycles and found some intereting articles:
The lunar cycle: effects on human and animal behavior and physiology
Lunar Cycles and Menstrual Cycles
The Wikipedia entry on the Lunar Effect has this to say:
The notion behind the lunar effect has fascinated many behavioralists and warranted many experiments and studies. Most experiments, however, have found no correlation between the variables and, thus, refuted the theory.
There are some studies which have results the researchers claimed supported the theory. For example, a study concluded that schizophrenic patients show signs of deterioration, in terms of quality of life and mental well-being, during the time of a full moon. Some researchers have claimed that there were strong positive correlations between physiological changes such as induced seizures in epileptic and non-epileptic people and the full moon period in studies they conducted. One study concluded that a statistically significant correlations for gastrointestinal bleeding among males in particular during this time. However, most of these findings are based on small-scale research.
On the other hand, the majority of scientific research seems to refute the theory of the lunar effect. Psychologist Ivan Kelly of the University of Saskatchewan (with James Rotton and Roger Culver) did a meta-analysis of thirty-seven studies that examined relationships between the moon’s four phases and human behavior. The meta-analysis revealed no correlation. They also checked twenty-three studies that had claimed to show correlation, and nearly half of these contained at least one statistical error. Kelly, Ronnie Martins, and Donald Saklofske evaluated twenty-one studies of births related to the phase of the moon and found no correlation. The scientific data “supports the view that there is no causal relationship between lunar phenomena and human behavior”. (Diefendorf 2007:113)
A study of 4,190 suicides in Sacramento County over a 58-year period showed no correlation to the phase of the moon. A 1992 paper by Martens, Kelly, and Saklofske reviewed twenty studies examining correlations between Moon phase and suicides. Most of the twenty studies found no correlation and the ones that did report positive results were inconsistent with each other.
Psychologist Arnold Lieber of the University of Miami reported a correlation of homicides in Dade County to moon phase, but later analysis of the data – including that by astronomer George Abell – did not support Lieber’s conclusions. Kelly, Rotton, and Culver point out that Lieber and Carolyn Sherin used inappropriate and misleading statistical procedures. When more appropriate tests were done, no correlation between homicides and the phase of the moon was found.
Astronomer Daniel Caton analyzed 70,000,000 birth records from the National Center for Health Statistics, and no correlation between births and moon phase was found. Kelly, Rotton, and Culver report that Caton examined 45,000,000 births and found a weak peak around the third quarter phase of the Moon, while the full moon and new moon phases had an average or slightly below average birth rate.
In 1959 Walter and Abraham Menaker reported that a study of over 510,000 births in New York City showed a 1 percent increase in births in the two weeks after full moon. In 1967 Walter Menaker studied another 500,000 births in New York City, and this time he found a 1 percent increase in births in the two-week period centered on the full moon. In 1973 M. Osley, D. Summerville, and L. B. Borst studied another 500,000 births in New York City, and they reported a 1 percent increase in births before the full moon. In 1957 Rippmann analyzed 9,551 births in Danville, PA and found no correlation between the birth rate and the phase of the moon 
A fifteen month study in Jacksonville, Florida also revealed at least no lunar effect on crime and hospital room admittance. In particular:
- There was no increase in crime on full moons, according to a statistical analysis by the Jacksonville Police Department. Five of the fifteen full moons had a higher than average rate of crime while ten full moons had a lower than average rate. The higher-than-average days were during warmer months.
- Statistical analysis of visits to Shands Hospital emergency room showed no full moon effect. Emergency room admissions consistently have more to do with the day of the week. 
Here is a website about cycles in general. It covers every type of cycle including astronomical and astrological.