When was the longest recorded solar eclipse in history?

Not all solar eclipses are equal – even if we ignore partial and annual solar eclipses, some are more impressive than others. Part of the growing excitement about next month’s North American solar eclipse is how much longer it will last than the 2017 equivalent, leading to questions like: When was the longest solar eclipse of all? And how long can a solar eclipse theoretically last?

The longest total solar eclipses aren’t what they once were – you might even say they’re a shadow of their former selves. In the past, eclipses could be much longer and undoubtedly more terrifying events. However, that was millions of years ago, when the moon was closer to the Earth.

Although the Moon was speeding through its orbit at the time, its extra apparent size meant it could block the Sun even if it wasn’t perfectly in front. So if you want to go back to the days of the dinosaurs, there would have been some epic eclipses that lasted longer than anything we encounter today.

Unfortunately, we don’t think there were Ceratosaurus clockmakers to time the event. Furthermore, our models of the movements of the celestial bodies, while impressive, lose their accuracy the further back you go. We don’t know exactly when the eclipses occurred tens of thousands – let alone millions – of years ago, so we can’t specify the dates of particularly long eclipses.

Therefore, any search for a record breaker should be limited to those records that have been measured by someone, or at least recorded as having happened.

The longest accurate measurement of a total solar eclipse was on June 20, 1955, when the sun was completely blocked for seven minutes and eight seconds. This eclipse was visible from Sri Lanka and parts of Southeast Asia, although most places along the path would have seen a slightly shorter event.

There have been longer eclipses throughout history, but in 1955 we saw the longest totality (blue lines) that humanity has ever measured.

There have been longer eclipses throughout history, but in 1955 we saw the longest totality (blue lines) that humanity has ever measured.

That record won’t last forever. In 2150 there will be a solar eclipse lasting 7 minutes and 14 seconds, so assuming we can keep civilization together until then, this one will be the longest at six seconds.

However, the time that the solar eclipse will be on the Sun in 2150 will be quite short. Eighteen years later, a solar eclipse will last no less than 7 minutes 26; one three seconds longer will still occur in 2186 at 7 minutes and 29 seconds. As we’ll see below, today that’s almost as long as a solar eclipse can last. The end of the 22nd century will truly be a golden age for eclipse chasers, although the path of totality barely touches land for the first of these.

However, humanity has probably witnessed eclipses for longer than 1955, even though we were not in a position to time them precisely. The oldest written record of a solar eclipse comes from the Chinese text the Shujing and is said to refer to a solar eclipse on October 22, 2137 BCE, although Irish petroglyphs may refer to an eclipse 1200 years earlier, on November 30, 3340 BCE.

In that time, there have been more than two dozen that have exceeded the 1955 event, according to NASA. We don’t have data for all of them. For example, the solar eclipse of June 9, 1062 occurred almost entirely over the Pacific Ocean, but lasted 7 minutes and 20 seconds according to modern calculations.

However, if we rely only on calculations, we can say that the longest period in that period was in 743 BC. when part of the Indian Ocean was in darkness for 7 minutes and 28 seconds. No doubt people in the areas where the eclipse’s path touched land were baffled by it, but they lacked the technology to measure it.

The length of a solar eclipse depends on the orbits of both the Earth and the moon, neither of which are perfectly circular. When Earth is farthest from the sun, our star takes up slightly less of the sky and can therefore be completely blocked for longer. Conversely, when the moon is closest, it appears larger and can block more. It also helps to be close to the equator to maximize the speed at which the Earth rotates the observer, slowing the relative speed of the moon’s shadow. Eclipses also last longer when the sun and moon are almost directly above the horizon, rather than close to the horizon.

Taking all this into account, the maximum length for a solar eclipse under current conditions would be 7 minutes and 31 seconds, according to calculations made. by Isabel Martin Lewis of the US Naval Academy. However, given how perfectly the celestial bodies must align, it is not surprising that we have been unaware of anything for so long. It is indeed astonishing that the examples mentioned above came so close.

The factors Lewis identified help explain why next month’s eclipse, while far from a record, will last longer than most. Earth’s distance from the sun will be only slightly further than average, but the moon will be only a day beyond perigee, or its closest point to Earth. The path of totality starts quite close to the equator, although it ends quite far north, and for much of the time the sun and moon will be high in the sky.

In other words: of the four factors, this solar eclipse scores well on two factors and mediocre on the other factors. These factors combine for a maximum total duration of 4 minutes and 28 seconds, as seen in Mexico. By comparison, 2017 never lasted longer than 2 minutes and 40 seconds.

There are, of course, people who will try to extend eclipses by putting themselves in planes – even supersonic ones – to race against the moon’s shadow. However, let us ignore such deceivers. If you want so badly to keep the moon between you and the sun, join the Artemis mission and do it the right way.

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