Even the most placid of astronomers can be sorely provoked by being dubbed an “astrologer”. Etymologically speaking, it’s an understandable mistake: the term astrology derives from the Greek for star and “logos” meaning to study, while “-nomy” is merely an exercise in labelling.
And historically, studies of celestial objects were motivated by the belief they influenced events on Earth, including the fate of humans.
Regrettably, however, that led to barmy fortune-tellers bagging the grand title of astrology, while astronomers had to settle for a more mundane-sounding vocation.
Yet ironically, astronomers have done more than anyone to demonstrate the validity of the ancient belief underpinning astrology.
While we are no more likely to meet an exciting new friend if Mars is in alignment with Jupiter, there is no doubt that these celestial bodies affect our planet as a whole.
These links go beyond the obvious, such as the role of the Sun and Moon in the tides. The biggest climatic upheavals experienced by our planet are now known to be under the influence of the other planets in our solar system.
Through their gravitational tugging, the Moon and planets distort the shape of the Earth’s orbit and the tilt of its axis to its orbit, causing subtle changes in the intensity of sunlight reaching us.
By altering the level of heating reaching different latitudes, these changes are now thought to play a key role in triggering the huge expansion in polar ice characteristic of an Ice Age.
But now astronomers think they may have uncovered another “astrological” connection between the Earth and its fellow planets – one with an impact on humans that beggars the trivia of astrology.
At its heart is a curious coincidence noted by astronomers more than 150 years ago. If the number of sunspots appearing on the disk of our nearest star are plotted over time, they follow a distinct pattern, rising and falling over a period of about 11 years.
This is curiously close to the 11.9 years that it takes Jupiter, the biggest planet in the solar system, to complete one orbit of the Sun.
It is always hard to know what to make of such “coincidences”; all too often they prove to be the product of nothing more than random chance.
But in 1852, the Swiss astronomer Johann Wolf showed that despite its great distance, Jupiter has more gravitational effect on the Sun than any other planet. He went on to develop a theory that seemed to account for sunspot numbers via the influence of Jupiter and other planets.
As sunspots are a symptom of solar activity, and this in turn directly affects the Earth, Wolf’s ideas sound uncomfortably close to astrology.
This doubtless explains why the notion of planetary influence on the Sun was hastily dumped at the start of the 20th century, following the discovery of a link between sunspots and the solar magnetic field.
Clearly, there could be no connection between the gravity of the planets and the magnetic field of the Sun. But now a team led by Dr José Abreu, of the ETH Zurich Institute for Geophysics in Switzerland, has rekindled the controversy with impressive evidence for precisely such a link.
To make their case, the team has examined records of solar activity far more extensive than those used by Wolf, who could only go back as far as the mid-17th century, and the first telescopic observations of sunspots by Galileo.
Dr Abreu and his colleagues have exploited the fact that changes in the sun’s magnetic field affect the levels of cosmic rays smashing into the Earth’s atmosphere – which in turn create isotopes that get trapped in polar ice and tree rings.
By analysing the rise and fall in levels of these isotopes, the team has managed to reconstruct the peaks and troughs in solar activity covering more than 9,000 years.
Armed with so much data, they have been able to look for patterns in the activity far more subtle than those found by Wolf. And what they have found broadly confirms his idea of a planetary influence on the Sun.
Publishing their findings in the current issue of the journal Astronomy & Astrophysics, the team stresses that the planets cannot be the prime driver for the 11-year cycle of solar activity.
If that were so, the orbits of the planets would change noticeably through the energy needed to drive the activity. But the planets can and do seem capable of affecting the processes that generate the Sun’s magnetic field.
Analysis of the isotope data has uncovered a set of cycles of solar activity ranging from about 85 to more than 500 years, each of which appears to be linked to planetary cycles.
All of which sounds pretty esoteric until one ponders the implications. Every so often, these cycles combine to produce periods of especially high or low activity.
And when they do, the effect on the Earth can be dramatic. Or, rather, has been dramatic – as the existence of such epochs is already well-accepted, even if their cause has not been.
Astronomers have identified several periods in recent history when usually high or low solar activity coincided with anomalous conditions on Earth.
Among them is the so-called Medieval Warm Period, lasting from about 1000 to 1250, and the so-called Little Ice Age, which lasted between about 1350 to 1850.
Each coincides with peaks and troughs in solar activity triggered by the planets, and to events of major historical significance. For example, the bitter winters of the Little Ice Age caused mass starvation and social upheaval in Europe during the 16th and 17th centuries.
The idea that the position of the planets control the kind of day we will have is so crazy that even many astrologers reject it as nonsense.
Yet the emerging evidence for planets influencing the Sun and thereby global events suggests that the real problem with astrology is that its claims were simply too modest.
Robert Matthews is visiting reader in science at Aston University, Birmingham, England