When we wish upon a falling star, we appeal to an ancient belief that the stars represent our souls and a meteor is one falling into the hereafter. In Teutonic mythology, for example, your star was tied to heaven by a thread, spun by the hands of an old woman from the day of your birth, and when it snapped, the star fell and your life had ended.

The Greek philosophers were the first to speculate on the nature of things without regard to ancient myths. Especially the world views of Aristotle of Stagira (384–322 BC) in his 350 BC book Meteorology were widely quoted for over two thousand years, embraced by Christian religion, and passionately defended until into the eighteenth century. The Greeks held that all matter in the Universe is made of the elements “earth,” “water,” “air,” and “fire.” Aristotle was of the opinion that shooting stars, because of their rapid motion, occurred relatively nearby in the realm of the element “fire” above the layer of “air” that is now called our atmosphere. He believed that shooting stars were not caused by the falling of stars, but were caused by thin streams of a warm and dry “windy exhalation” (a mixture of the elements fire and air) that had risen from dry land warmed by the Sun. Those exhalations would rise above the moist parts of the atmosphere containing clouds (mixtures of “air” and “water”), into the realm of “fire.” The more and the faster a thing moves, the more it is heated by friction and the more apt it is to catch fire. Hence, when the motion of the heavenly bodies stir the “fire,” the exhalations can burst into flame at the point where they are most flammable. Once ignited, the flame would run along the path of the vapor and thus create a “torch” – what we now call either a fireball or a bolide (βολιδεσ) meaning “thrown spear.”

Theory and observations go hand in hand in our efforts to understand nature, but observers are not always remembered in the same way when discussing the gain made over the years. Their bold ventures into the cold and dangerous world painstakingly paved the path to wisdom, and those before us, many now forgotten, found that path much less traveled. This section recalls some of past travels in the pursuit of meteor showers.

The anticipated 1899 Leonid return prompted some astronomers to rise above the clouds. In France, Jules Janssen (1824–1907), first director of the Observatory of Meudon, and his colleague M. W. de Fonvielle, organized a balloon flight to bring visual observers above the ground fog, with support of the French Society of Aerial Navigation. Before that, meteor showers had often been seen from hot air balloons in the wind-still early morning hours before sunrise (Fig. 12.1) and de Fonvielle had earlier viewed the Leonid shower of November 13/14, 1867, above clouds over Paris in what was probably the second airborne astronomical expedition (the first being a total solar eclipse observation that year). Now, everybody wanted to ascend in a balloon to view the Leonids. A German balloon launched from Strasbourg fell at Fanxault, causing one serious injury, while a British balloon was nearly lost at sea. Janssen's 1898 balloon mission was flown by Russian astronomer Gavriil Adrianovich Tikhov, then stationed at Meudon. Rates had been high, but there was no storm that year. In 1899, there were five balloon flights. On the night of November 15/16, it was a woman, 38 yr old San Francisco born astronomer Dorothea Klumpke (1861–1942), then working at the Observatoire National de Paris, who was chosen to be the observer. “I do not know what good fairy overheard my wish to take a trip in the blue sky,” Klumpke wrote of her voyage in the balloon called Le Centaure. As Klumpke waited to go aloft, she knew of the disappointing reports from the previous night.

The mystery of the Quadrantid shower (Fig. 20.1) has always been its source. The Quadrantids have a peak ZHR ∼ 130/h, which is the highest of all known annual showers. Unfortunately, the shower is only 8.5 h FWHM wide, and very difficult to observe because of frequent bad weather in early January and a radiant that is in under-culmination at midnight.

Even after the shower was first recognized in January of 1835 (Chapter 1), it took an 1862 report from a lady in Connecticut, stating that she had observed an unusually large number of shooting stars early in the morning of January 2, to first get Edward C. Herrick and then other observers excited. Among those was Alexander S. Hershell, who in 1864 gave the “Shooting Stars of January” their modern name, finding a radiant point at “c Quadrantis Muralis” in the now defunct constellation Quadrans Muralis. In the non-English speaking world, the shower is better known by the name of Bootids. In a modern star atlas, the radiant is at the corner of the constellations Bootes, Hercules and Draco.

The search for its parent first took a clue from the dramatic and rapid evolution of the orbit, discovered in the early modeling by Salah E. Hamid and Mary N. Youssef. This 1963 study added the effect of all planetary perturbations on test particles, six in total, over many orbits. Results were confirmed later by others using more modern computering tools. They found that the orbit had rotated in a nutation cycle from a low inclination of i ∼ 13° and low perihelion distance q ∼ 0.1 AU some 1500 years ago, to its current high i ∼ 72° and q ∼ 0.78 AU (Fig. 20.2). The orbit will continue to evolve to a peak value of i ∼ 76° and q ∼ 1.0 AU about 1000 years from now, before decreasing again.

Meteoroid streams in space used to be invisible, their existence illuminated only by the meteor showers they caused on Earth. Then, in 1983, dust trails were discovered in the orbit of short-period comets. Dust grains absorb visible light, warm up, and re-emit that energy as thermal emission in the mid-infrared.

My Alma Mater at Leiden Observatory was deeply involved in the interpretation of data from the monumental 1983 all-sky survey of heat emissions at the mid-infrared wavelengths of 12, 25, 60, and 100 μm by the InfraRed Astronomical Satellite (IRAS), a joint project of the USA, UK, and the Netherlands. The observatory had a vested interest in the topic of interstellar dust, with my professor, Harm Habing, being one of the leading investigators of IRAS. As in so many astronomical institutes, meteor studies were delegated to amateurs. I was such an amateur, joining the ranks of the Dutch Meteor Society two years earlier.

When the news spread that the images from IRAS showed dust trails in the path of comets, I immediately suspected a link with meteor outbursts. It was the excellent 1986 report by Mark Sykes and coworkers, with details of the width of the trails and estimates of the sizes of the dust grain, that first alerted me to the trails, although the discovery was made by John Davies a few years earlier and published in a paper that discussed other things as well.

Apart from the Leonids, Ursids, and Perseids, there are a handful of other known Halley-type comet induced showers with past meteor outbursts, and some that are not so well known. In addition, I will report here on an ongoing investigation into a mechanism of comet ejection peculiar to Halley-type comets and how that may manifest as meteor showers on Earth.

18.1 The Halley streams

The Orionid shower was among those discovered in the years following the 1833 Leonid storm. It is a relatively strong annual shower with a peak of ZHR = 25 around October 22. The parent is comet 1P/Halley itself, now in an orbit passing a far +0.151 AU from Earth.

Hence it came as a surprise when, in 1993, the most active and experienced visual observer of the Dutch Meteor Society, amateur astronomer Koen Miskotte, reported an outburst of meteors from the Orionid shower (Fig. 18.1). Observing under a good sky limiting magnitude Lm =+6.6m in the two nights of October 16/17 and 17/18 (peak at λ⊙ ∼204.5°), rates were 2–3 times higher than normal. In that second night, Koen saw a −5m Orionid fireball, another of −4m and two of −3m from R.A. = 90.3°, Decl. = 14.8°. This is very unusual since Orionids are quite faint (population index χ = 2.9) and as Koen recalls I had never seen Orionids brighter than −2 before in my career as a meteor observer. And I should know, because I watched this shower in seven previous years. Hans Betlem, observing from Sinderen in the eastern part of the Netherlands, confirmed the high activity. Some of these bright meteors were photographed, but only one from two sites simultaneously. That Orionid with a −5m end flare had a radiant at R.A. = 90.1±0.2°, Decl. =+15.4±0.2° and speed Vg = 67.5±0.7 km/s. Its orbit had a higher than usual perihelion distance at 0.613±0.013 AU (Table 7).

Meteor showers are a threat to satellites in orbit and an early warning of comet impacts that could one day threaten our very existence. Each year, Earth is hit by 20 000 tons of meteoroids, <1 kg in mass, 10 million meteors brighter than +6.5m, at a rate of ∼1000 visible meteors per second, but by only one superbolide. And only once every 100 million years does a 10 km sized minor planet hit. Despite these disparate frequencies, each group brings in about the same amount of mass (Fig. 32.1).

32.1 Giant impacts

A 10 km sized minor planet would instantly blind any casual observer by its blazing −45m fireball and create a 100 km sized crater from the explosion on impact, if not all of the cosmic speed is dissipated in the atmosphere. The last eye witness of such a giant impact was likely to have been a dinosaur 65 million years ago, when all its relatives but the birds died after a 10 km minor body hit the Yucatan Peninsula of Mexico in what was then a shallow sea. The 180–300 km diameter crater is now buried by 300–1000 m of limestone. At that time, much of the asteroid or comet survived the atmosphere and when it hit the ground, so much energy was released that the rock (a limestone ocean bed rich in carbonates and sulfates) was vaporized out to a distance of 6–12 km from the impact point. The vapor was super hot at thousands of degrees Celsius, expanding rapidly into a plume rising from the ground into space along the fireball track and ultimately encircling the whole Earth. For thousands of miles around the crater there was a rain of molten droplets (tektites) and debris. Low-lying areas near the coast of the shallow sea were inundated by a tsunami. For weeks, the impact heat of the explosion and the heated atmosphere would have caused fires that would have released soot and carbon dioxide into the atmosphere.

The Perseids are the amateur astronomer's main entertainment on sultry summer nights. The Perseids have been around as long as there are records (Chapter 1). They are caused by the largest comet to frequent Earth for thousands of years past, 109P/ Swift–Tuttle, which will continue to frequent Earth for thousands of years to come. When the comet returned in 1992, a series of meteor outbursts were observed that led to my first successful meteor storm chase. One year later, meteor outbursts were the astronomical theme for a Mediterranean cruise and all of America went out to look at the shooting stars.

These meteor outbursts sparked a debate on whether they were caused by young dust trails or the Filament of older trails. In this chapter, I will argue that they were mostly from older trails, making it appropriate that the name ‘Filament’ was first given to these outbursts.

17.1 The 1979–1981 Perseids

Perseid meteoroids approach Earth from a northern direction (Fig. 17.1) with a radiant in the constellation of Perseus at R.A. = 48°, Decl. =+58°, just below the “W” of Casseiopeia.

Parent comet 109P/Swift–Tuttle was last seen in 1862. In 1973, Brian Marsden,at the time director of the IAU's Bureau for Astronomical Telegrams, recalculated the orbit of the comet and predicted a return on September 16.9, 1981 (±1.0 yr), suspecting that a comet seen by astronomer Pehr Wargentin at Uppsala in 1750 was an earlier sighting.

In the early nineties, satellite impact hazard models erroneously assumed that geocentric meteor radiants were spread evenly over the sky relative to the moving Earth. Jim Jones and Peter Brown in Canada and Andrew Taylor at Adelaide took stock of our knowledge of the overall radiant distribution from radar data by tackling the observing bias. They identified six principal source areas on the sky. Next to the North and South Apex source from Halley-type and long-period comet showers (15–28% of meteoroids), and the Helion and Antihelion sources of the ecliptic Jupiter-family comet streams (30–40% each), they also confirmed earlier reported North and South “Toroidal” sources at high ∼67° latitude (Fig. 28.4). These meteoroids moved in nearly circular orbits at steep angles to the ecliptic plane. They had a very small semimajor axis a ∼ 1.0 AU, not so elongated e ∼ 0.3, and a prograde high inclination (i ∼ 60°). The Toroidal meteoroids surround Earth in a volume that has the shape of a car tire, with Earth on the open inside of the torus.

Toroidal meteoroid orbits dominate the radar orbit database and are a separate source from ecliptic meteoroids only because of the competing factors of increased likelihood of detection by radar and of decreasing numbers with increasing latitude of the radiant and entry speed of the meteors. After correcting for bias, the Toroidal source all but disappeared, with only 3–6% of all meteors coming from this region. Jim Jones has since taken the view that the Toroidal meteoroids are merely the high-inclination tail of a continuous distribution of dust from the Helion and Antihelion sources.

Some 100 out of 275 streams extracted from the Harvard Radio Meteor Project radar data by Zdenek Sekanina are Toroidal streams, most in the fall and the winter. In Table 7, I mainly list streams that were confirmed by other techniques, and that includes most of Sekanina's Antihelion, Helion, and Apex streams, but very few of his Toroidal streams.