Perseids

Characteristics

The stream of debris is called the Perseid cloud and stretches along the orbit of the comet Swift–Tuttle. The cloud consists of particles ejected by the comet as it travels on its 133-year orbit. Most of the particles have been part of the cloud for around a thousand years. However, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1865, which can give an early mini-peak the day before the maximum shower. The dimensions of the cloud in the vicinity of the Earth are estimated to be approximately 0.1 astronomical units (AU) across and 0.8 AU along the Earth's orbit, spread out by annual interactions with the Earth's gravity.

The shower is visible from mid-July each year, with the peak in activity occurring between 9 and 14 August, depending on the particular location of the stream. During the peak, the rate of meteors reaches 60 or more per hour. They can be seen all across the sky; however, because of the shower's radiant in the constellation of Perseus, the Perseids are primarily visible in the Northern Hemisphere. As with many meteor showers the visible rate is greatest in the pre-dawn hours, since more meteoroids are scooped up by the side of the Earth moving forward into the stream, corresponding to local times between midnight and noon, as can be seen in the accompanying diagram. While many meteors arrive between dawn and noon, they are usually not visible due to daylight. Some can also be seen before midnight, often grazing the Earth's atmosphere to produce long bright trails and sometimes fireballs. Most Perseids burn up in the atmosphere while at heights above 80 kilometres (50 mi).

Largest Perseid meteoroids have masses of 7 kilograms (15 lb).

Peak times

Historical observations and associations

Some Catholics refer to the Perseids as the "tears of Saint Lawrence", suspended in the sky but returning to Earth once a year on August 10, the canonical date of that saint's martyrdom in 258 AD. The saint is said to have been burned alive on a gridiron. His manner of death is almost certainly the origin of the Mediterranean folk legend claiming that the shooting stars are the sparks of Saint Lawrence's martyrdom. The legend holds that during the night of August 9 to 10, cooled embers appear in the ground under plants; these embers are known as the "coal of Saint Lawrence".

The transition in favor of the Catholic saint and his feast day on August 10, moving away from pagan gods and their festivals – a process known as Christianization – was facilitated by the phonetic assonance of the Latin name Laurentius with Acca Larentia, a goddess previously celebrated during the summer period alongside Priapus, as a fertility deity. Among the Romans, it was believed that the trails of the Perseids represented the benevolent rain of Priapus' seed. In this context, the god's cosmogonic phallus acted as a life-giver, blessing the fields and promoting fertility. During the same period, phallic processions and other sexual rites were common. Christianity, which had a different relationship with sexuality and generativity compared to Greco-Roman culture, replaced this sexual connotation with a reference to martyrdom.

In 1836, Adolphe Quetelet wrote: J'ai cru remarquer aussi une fréquence plus grande de ces météores au mois d'août (du 8 au 15) "I think I noticed also a greater frequency of these meteors in the month of August (from 8 to 15)". After studying historical records, he predicted a peak on 10 August. He then wrote to other astronomers, who confirmed this prediction on the night of 10 August 1837. Quetelet missed the shower due to bad weather.

In 1866, after the perihelion passage of Swift–Tuttle in 1862, the Italian astronomer Giovanni Virginio Schiaparelli discovered the link between meteor showers and comets. The finding is contained in an exchange of letters with Angelo Secchi.

In 1992, Comet Swift–Tuttle returned to the Earth's vicinity, producing strong Perseid meteor outbursts in August 1991, 1992, and 1993, with peak rates of several hundred meteors per hour observed. Finnish astronomer Esko Lyytinen calculated that the Earth could enter into an extra thick debris field left behind by Comet Swift–Tuttle in 2028, which could possibly produce a Perseids meteor storm on the night of August 11–12, 2028. A peak rate of at least 1,000 meteors per hour is possible at the zenith, which was projected to be around 1:30 am EDT (05:30 UTC) on August 12.

In popular culture

In his 2006 novel Against the Day, American novelist Thomas Pynchon refers to the Perseid meteor shower being watched by three characters west of the Dolores Valley after playing a game of tarot. In the TV series Curious George, season 7 episode 1b, George and his friends Allie and Bill hunt for the Perseids, which they believe are creatures that look like purses. At the end of the episode, Allie's grandfather Mr. Renkins says that the Perseids is a meteor shower happening in early August.

John Denver's song "Rocky Mountain High" references the showers with the lyric, "I've seen it raining fire in the sky."

General and cited references

• Littman, Mark, The Heavens on Fire: The Great Leonid Meteor Storms, Cambridge, Cambridge University Press, 1998. ISBN 0521624053. Chapter 6, "The Discovery of the August Meteors", pp. 83–100.