The modern worldview does not tell us, why for our ancestors equinoxes where so important (more important rituals than in winter or summer solstices were performed).
Perhaps, the first from scientists, which realized the importance of equinoxes, were investigators of terrestrial magnetism some 150 year ago (Svalgaard et al, 2002).
It has become clear, that for occurrence of geomagnetic storm important is the position of Earth’s self rotating axis relative to Sun (Yoshida, 2009). Not likely that coupling of a weak geomagnetic field with solar wind can make a geomagnetic storm.
Furthermore, Richter’s law in seismology states, that in the 3 months around equinoxes there are more earthquakes that in the 3 months around solstices. (Lomnitz, 1994).
Chronobiologists Farbrige and Leatherland (1987) found out, that lunar cycles in fish fries are influenced by spring equinox (light conditions where there is 12 hour light and 12 hour dark).
Thus equinoctial time can be characterised as time with increased interaction of RLF’s of the Earth and the Sun. Not surprisingly, pacients with bipolar disorder and seasonal affective disorder feel this. Birthday in equinox time has been associated with larger possibility of some diseases (http://www.demogr.mpg.de/books/drm/002/5.pdf).
Animal mating seasons typically are connected to that “three months around equinoxes”.
Interestingly, spring and autumnal equinoxes differ by influence to nature. Thus, test-tube babies can be far better produced in spring, that in fall (Vahidi et al, 2004).
Similarly, draft calculations show, that Sun- Jupiter opposition time (with Jupiter in perigee) may significantly influence Earth (possibly including earthquake triggering – for example 7.2 earthquake in Sept. 29, 2010 and 7.1 earthquake in Oct 23, 2011).
Farbridge K. , Leatherland J. Lunar cycles of coho salmon, Oncorhynchus Kisutch. I. Growth and feeding. J.exp.Biol. 129, 165-178, 1987.
Lomnitz C. Fundamentals of earthquake prediction. Wiley, 1994. http://www.springerlink.com/content/w50882kp523053k0/
Svalgaard L. et al. The semiannual variation of great geomagnetic storms. Geophysical Research Letters, 29, 1765, 2002.
Vahidi A. The Relationship between Seasonal Variability and Pregnancy Rates in Women Undergoing Assisted Reproductive Technique. Iranian journal of reproductive medicine, 2, 82-86, 2004.
Yoshida A. Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity. Ann. Geophys., 27, 1909-1914, 2009.