On 12 August, a cluster of celestial events coincide, a rare event that may inspire not just awe, but theories with no basis in science. The Moon’s shadow will fall across a patch of Earth, viewable as a solar eclipse from parts of our planet’s surface. Before dawn, six other planets will appear strung across the sky, their positions predictable decades in advance.
After dark, Earth will pass through the debris trail of Comet Swift-Tuttle, producing the annual Perseid meteor shower, a spectacle of small particles burning up as they strike our atmosphere. This year, it happens to overlap with a new moon, the darkness of which should brighten tonight’s ‘shooting stars’ for our eyes.
Earth can expect 50-100 meteors per hour under ideal conditions, according to Nasa, the US space agency. Tonight’s minimal lunar glow would also let stargazers gaze at a hazy band of the Milky Way, our galaxy. The next ‘moonless’ Perseid peak of this kind is 19 years away.
Big moments that set astronomy abuzz, however, tend to feed astrology too.
Before an apparent line-up of Jupiter, Mercury, Mars, Saturn, Uranus and Neptune can join a sky dazzle to forge forecasts of human affairs, the basic science of celestial cycles calls for attention.
Those planets orbit the Sun broadly in the same plane, so from Earth they appear to trace the same ecliptic path across the sky, even if Wednesday’s cluster view is rare.
There is no scientific evidence of any force these planets exert on earthly species, either individually or combined. Why, then, do claims of their sway hold appeal?
In 1948, psychologist Bertram Forer asked students to take a ‘personality test’ and then gave everyone more or less the same glowing report of its results. Most students rated it accurate, even though its flattery was based on a dummy test and common to all. This came to be known as the ‘Barnum effect,’ after a showman who spoke of there being something for everyone.
Horoscopes are an example. Aimed at a broad audience, they can be confident that predictions which seem to pan out as foretold will be recalled while others are forgotten. Confirmation bias reinforces the effect.
Some of it may be evolutionary. Humans are pattern-seeking animals. For our ancestors, every rustle in the wild was a potential predator. Today, investors seek signals in random market movements, political analysts turn messy events into narratives of inevitability and businesses identify ‘one thing’ behind their success, with luck, timing and the rest given no credit.
Perhaps the same instinct creates a market for personalized sky readings.
Just as correlation is not causation, however, a pattern is not necessarily an explanation. Science suffices to explain why Wednesday’s sky show will vary from one place to another.
A total eclipse of the Sun will be visible only along a narrow path spanning Greenland, Iceland, north Russia, parts of Spain and a bit of Portugal past sundown in India. Meteor and Milky Way visibility will depend on factors like terrestrial glare and cloud cover.
Still, cosmic displays like these can make anybody’s jaw drop in awe. They are a reminder of the universe around us and how little we know of it. This should stoke not superstition but a quest for knowledge acquired through repeatable tests of scientific hypotheses. Einstein’s ‘gravitational red-shift’ was confirmed by telescopes long after he wrote of it.
Claims of cosmic effects on our lives must face equally rigorous scrutiny. And for space-age success, science must lead the way.