The image above shows a depiction of the great Leonids meteor storm that occurred on November 13th, 1833 in which more than 72,000 meteors per hour fell to Earth, and which according to one observer caused the night sky to radiate so bright with falling stars that “people were awakened believing that their house was on fire!”
Awe Inspiring Meteor Storm
While the Leonids meteor shower is an annual event, every 33 years it becomes even more intense as the comet 55P/Temple-Tuttle makes its closest approach to the Earth and Sun. The Leonids Meteor Storm of 1833, however, was unusually prolific and became one of the most spectacular astronomical sights ever seen in the modern era, with many people believing that the world was coming to an end. It also occurred at a time before electric street lights had been invented, and the Moon had set in the early evening providing North America with an unobstructed view of the sublime celestial phenomenon.
Needless to say, the story was picked up in various newspaper reports as the “night the stars fell”, with the following description of the Wall family’s experience giving an insight into thoughts and feelings of witnesses at the time. As the report written by Bruna McGuire and Betty Wall explains:
“The stars showered down so thickly and fast that it looked as though every star in the heavens was falling. When they touched the ground, they burst and drifted away. Stars were still falling when the sun arose the next morning. Never before had there been such a sight witnessed, nor has there been since the greatest meteoric display of our age.”
The Leonids in History
From a purely historical perspective, the Leonids meteor shower is one of the oldest known. In the year 902 AD, Chinese astronomers described the night “stars fell as rain”, with the event also picked up by observers in Egypt and Italy. Much later, anecdotal records from 1630 recount tales of unusually large numbers of meteors two days after the funeral of Johannes Kepler, which many authorities of the time saw as a “salute to Kepler from God”.
Other accounts of unusually large numbers of meteors during the month of November include those from 1799, when German scientist Humboldt and his companion reported the sighting from what is now Venezuela, over which it was said that a similar event had occurred in 1766. As Humboldt stated “thousands of fireballs and falling stars fell in a row for four hours, often with a brightness like Jupiter. Long smoke trails were left behind.”
Following the Great Leonids Meteor Storm of 1833, American astronomer Denison Olmsted described drew attention to the fact that no celestial phenomenon has ever occurred in North America “since its first settlement, which was viewed with so much admiration and delight by one class of spectators, or with so much astonishment and fear by another class.”
The really strange thing about the Leonids meteor shower is that while ordinary citizens were aware of the fact that it occurred in cycles, this simple fact had eluded scientists until Olmsted started an investigation that year concerning the origin of the meteors, and wrote a comprehensive report about his findings. In the process, Olmsted also overturned a 2,000-year-old doctrine developed by Aristotle that held that meteors were the fiery sparks of the remains of enormous gas bubbles that rose into the air, before exploding high above the ground.
When Olmsted observed the Leonids of 1833, he noticed that they appeared to originate from a fixed point in the constellation Leo, which made him realize that the meteors were entering the atmosphere from outer space. Using this observation as his point of departure, he calculated the meteors’ speed to be about 6.4 km/sec, which he thought was really, really fast, but which later turned out to be too slow by a factor of more than ten. Nonetheless, using simple trigonometry, Olmsted calculated the altitude at which the meteors became visible to be between 50 and 80 km, which turned out to be largely correct.
Calculating the size of the glowing meteors, however, presented Olmsted with something of a thorny problem. The role of friction in astronomy was largely uncharted territory in the early 1800’s, but using available knowledge, Olmsted’s calculations suggested that each meteor was up to about 1.6 km in diameter, as opposed to the tiny grains of dust that we now know meteors to be.
While Olmsted’s findings up to this point are interesting, his most important realization broke new scientific ground. Olmsted concluded that since the meteors were coming from outer space, their ultimate origin must be the disintegration of a body that periodically passes Earth relatively closely, and which leaves a trail of debris behind at each passing. Thus, as Earth moves through the trail of debris during its orbit around the Sun, the particles enter Earth’s atmosphere, resulting in spectacular meteor showers.
Sadly, though, many years passed before it was discovered that the source of the Leonids meteors is the comet 55P/Temple-Tuttle, which sheds relatively large amounts of debris as it approaches the Sun once every 33.2 years. Since the comet’s orbital plane around the Sun is relatively close to that of Earth, we pass through dense (relatively speaking) parts of the comet’s debris trail once every year, and usually between the 17th and 20th of November.
At first reading, one might wonder why the Leonids shower occurs every year, since the comet 55P/Temple-Tuttle orbits the Sun only once every 33 years. The reasons for this are rather complex, but in simple terms, the debris trails the comet leaves persist for long periods of time before radiation pressure from the Sun (among other forces) can disperse them.
In practical terms, no two orbits of comet 55P/Temple-Tuttle, or any other comet for that matter, are the same. Since the orbital period of the comet is not a near-integer number of years, the Earth-comet configuration is such that it cannot be repeated on successive returns of the comet. Additionally, since the distance between the comet and Earth does not remain constant throughout the comet’s orbital period, Earth passes through different parts of the debris trail at different times, thus resulting in more or fewer particles entering Earth’s atmosphere at different times.
Imagine the debris trail of comet 55P/Temple-Tuttle as a partial ring of dust that trails behind the comet and while the overall ring of dust persists for many years, each close perihelion causes a fresh discharge of material to be shed within the broader structure that partially disperses between returns of the comet. While the mechanics of the comet’s dust trail is extremely complex, repeated close approaches to the Sun has the effect of creating alternating areas of high and low density debris volumes within the broader debris trail that correspond to the comet’s 33-year orbital period.
The practical effect of this is therefore that once every 33 years, Earth encounters such a high-density debris trail within the broader trail, which is what happened in 1833, 1866, 1899, 1933, 1966, and 1999, with the next major storm expected to occur in 2031/2.
However, while the comet 55P/Temple-Tuttle will yet provide many more displays of spectacular celestial fireworks, its core is very small, and is currently only about 3.6 km in diameter. Given that between 10 and 13 metric tons of material is deposited onto Earth during a major meteor storm, however, it will eventually disintegrate under the powerful gravitational influences of the Sun and other solar system bodies in the not too distant (astronomically speaking) future.