Humans have been captivated by the beauty and mystery of eclipses for thousands of years. These celestial events have spurred countless legends, myths, and religious beliefs. But as much as humans have tried to predict them, eclipses remain one of the most challenging astronomical phenomena to forecast accurately. Despite considerable advancements in science and technology, the complexities involved in predicting eclipses continue to baffle even the most astute scientists. In this article, we delve into the fascinating history of eclipse predictions, the science behind them, and the difficulties that astronomers face in forecasting them.
The coastal town of Exmouth in Western Australia will witness a total solar eclipse on April 20, 2023, making it one of the most spectacular astronomical phenomena to be observed. For centuries, eclipses have captivated human beings. Though the sun and the moon were the most captivating celestial bodies for ancient cultures to observe, it was the moon’s complex motion that made it hard to explain its orbit. Additionally, explaining the motion of the moon was the only issue that made Isaac Newton’s head hurt. During a lunar eclipse, Earth blocks sunlight that would otherwise illuminate a full moon, leading to a dimmed moon that appears to take on a bloody hue. Many cultures attached foreboding to such events and wondered when the next such occurrence might happen, leading to the discovery of the repeating characteristics of such events.
Various cultures around the world independently discovered that eclipses seem to occur on an 18-year cycle. Oral tradition suggests that this cycle was used for ceremonial purposes by Torres Strait Islanders in what is now Australia, and it was mentioned in written records by the Babylonians and Assyrians. This 18-year cycle, which can persist as a sequence for over a thousand years, is now known as a Saros cycle. The Saros cycle represents how long it takes for the sun-Earth-moon system to return to almost exactly the same triangular configuration. So, if a lunar eclipse is observed, another one can be expected 18 years later, visible from most places on Earth. After 54 years—three Saros cycles—the eclipse region should have returned to roughly the same position on Earth. But only very roughly, as it could be thousands of kilometers away from the previous observation spot.
Though ancient ancestors could predict lunar and partial solar eclipses, there is no evidence of people predicting the times and locations of total solar eclipses. For example, the famed Greek Antikythera Mechanism, an astoundingly complicated 2,000-year-old mechanical device used to predict the night sky, could calculate the 18-year Saros accurately, but it could not predict total solar eclipses at a precise place on Earth—just their timing. Entering the modern era of science, the first true prediction of a total solar eclipse (both in time and location) occurred in 1715 when Edmond Halley predicted a total solar eclipse that passed over his own house in London to within four minutes and 20 miles. Today, NASA uses pattern recognition to predict both solar and lunar eclipses for 1,000 years into the future, relying on about 38,000 repeating mathematical terms.
Although eclipses have directly driven advancements in mathematics and orbital mechanics, trying to predict and explain this phenomenon has forced humans to embrace the limits of our scientific knowledge. For those lucky enough to witness a total solar eclipse, contemplating this shared experience’s meaning to humans worldwide throughout the centuries can instill wonder and awe.
