The Leonid meteor shower peaks today. Its parent comet taught us where meteor showers come from.
Every year, as Earth regularly orbits the Sun, meteor showers repeatedly recur.
While August’s Perseids and December’s Geminids are very consistent meteor showers, exhibiting around 100 meteors-per-hour at their annual peak, the Leonids are far more variable. While 2019 might only see around 20 meteors-per-hour at its peak, a thrice-per-century meteor storm is associated with the Leonids, well-documented in many illustrations and accounts from the 19th and 20th centuries. Meteor storms can see rates exceeding 1000 meteors-per-hour: a tenfold increase over the typical Perseid or Geminid shower. (E. WEISS’S BILDERATLAS DER STERNENWELT (1888))
August’s Perseids and December’s Geminids are annually spectacular, but November’s Leonids have more astronomical importance.
A meteor storm is characterized by showers of shooting stars that are so intense, they occur every few seconds on average. The meteor storm of 1833, associated with the Leonids, was a legendary outburst. (ADOLF VOLLMY, ENGRAVING FROM 1889)
In contrast to their typically modest show, the Leonid display is spectacular every 33¼ years.
Engraving depicting the Leonids meteor shower, which is now associated with the comet Tempel-Tuttle, as seen over Niagara Falls in 1833. Dated 19th century. (Universal History Archive/Universal Images Group via Getty Images)
In 1833, the Leonids caused a meteor storm worldwide, producing 1,000+ meteors-per-hour.
This image depict the Leonid meteor shower, which in 1866 put on a spectacular display nearly equal to the great storm of 1833. The scene is set over Greenwich, London, 1866. The Leonids, named because they emanate from the area of the constellation Leo, are visible in the night sky during November. From Sun, Moon and Stars by Agnes Giberne. (Oxford Science Archive/Print Collector/Getty Images)
For each of the next 32 years, they were quiet, but then exploded once again in 1866.
Although he was unsuccessful in the endeavor to discover Neptune, Adams never attempted to falsely take credit for it. Even when credit was given to him, he always referred to the true discoverers, and did not count himself among them. But a few years later, he made a discovery that was arguably even more spectacular and enduring. (GEO KOMPAKT NR.21/DEZEMBER 2009, PAGE 138 (L), AND WIKIMEDIA COMMONS USER SKRAEMER (R))
John Couch Adams, famous for almost (but not quite) discovering Neptune, had a three-part idea.
The 1997 Leonid meteor shower, as seen from space. When the meteors strike the top of Earth’s atmosphere, they burn up, creating the bright streaks and flashes of light we associate with meteor showers. Occasionally, a falling rock will be large enough to make it to the surface, becoming a meteorite. (NASA / PUBLIC DOMAIN)
1.) What we observe as “shooting stars” or meteors are small, fast-moving dust grains burning up in our atmosphere.
The debris stream of a comet, like Comet Encke (shown here) or Comet Swift-Tuttle (which created the Perseids) or Comet Tempel-Tuttle (which causes the Leonids), is the cause of meteor showers on Earth and all other worlds in the Solar System. John Couch Adams’ 19th century identification of Comet Tempel-Tuttle with the Leonid meteor shower was the first link ever made between these two phenomena. (NASA / GSFC)
2.) Meteor showers recur annually when Earth passes through each dusty debris stream.
Although, for many comets or asteroids, there is a higher density of debris associated with the location of the main body, over enough time, the debris will get smeared out along the orbit to such a sufficient degree that the meteor shower can become very consistent year-to-year. The Leonids have not yet reached that stage, and as such, they still peak roughly every 33.25 years. (GEHRZ, R. D., REACH, W. T., WOODWARD, C. E., AND KELLEY, M. S., 2006)
3.) Every debris stream is spread-out, but has a point of maximum density, corresponding to meteor storms.
This four panel view shows the peak of the Leonid meteor shower during 1966, another one of the peak years that recur on a 33.25 year basis. Although the Leonids do recur annually, they are only spectacular roughly 3 times per century, when the densest patch of a cometary debris stream crosses Earth’s orbit. (AURA/NOAO/NSF)
His idea was speculative, but provable, assuming he could find the parent body.
Adams’ theoretical prediction of the orbit of the Leonid debris stream led to a path and an expected location of the parent body. The calculations he performed turned out to line up almost perfectly with the newly discovered Comet 55p/Tempel-Tuttle, discovered less than one year prior. (THE SKY LIVE 3D SOLAR SYSTEM SIMULATOR)
His experience calculating orbits while searching for Neptune proved indispensible, deriving a Uranus-crossing, 33¼ year orbit for the Leonids.
Comet Tempel-Tuttle, discovered in December 1865/January 1866 by two astronomers (Tempel and Tuttle) independently, turned out to match exactly the orbital parameters predicted by Adams. Each time it nears the Sun, it can be imaged by astronomers with telescopes, and seen by many skywatchers with nothing more than binoculars. These images from its last close pass in 1998/1999 showcase the brightening that occurs in the comet after passing perihelion (right) as opposed to just a month or so prior. (AKIMASA NAKAMURA, KUMA KOGEN ASTRONOMICAL OBSERVATORY, KUMA, EHIME, JAPAN)
It matched the newly discovered Comet Tempel-Tuttle almost exactly, ushering in the meteor shower-comet connection.
1999 was the most recent Leonid meteor storm, shown here as seen over the Azrak desert, 90km east of Amman. The storm packed up to some 1,500 meteors per hour visible with the eye. The Leonids — so called because they appear in the sky in the region of the constellation of Leo — are a stream of minute dust particles trailing behind the Tempel-Tuttle comet, which is spectacularly visible from Earth every 33 years. The next Leonid storm should occur in either 2032 or 2033. (JAMAL NASRALLAH/AFP via Getty Images)
The Leonids peak tonight, marking 153 years of humanity knowing the cause of these celestial fireworks.
Originating from the direction of the constellation of Leo, the Leonid meteor shower is most spectacular on a 33-year recurring basis. Very close to that peak, the meteor shower will be more active, as shown in this 1998, four-hour composite all-sky image, which captured approximately 150 meteors. We are more than halfway to the next peak, which should lie roughly 13 years off from today. (JURAJ TOTH (COMENIUS U. BRATISLAVA), MODRA OBSERVATORY)
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
Ethan Siegel is the author of
Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.