Persaid History

Perseid History

This is the most famous of all meteor showers. It never fails to provide

an impressive display and, due to its summertime appearance, it tends to

provide the majority of meteors seen by non-astronomy enthusiasts.

The earliest record of its activity appears in the Chinese annals, where

it is said that in 36 AD "more than 100 meteors flew thither in the

morning." Numerous references appear in Chinese, Japanese and Korean

records throughout the 8th, 9th, 10th and 11th centuries, but only

sporadic references are found between the 12th and 19th centuries,

inclusive. Nevertheless, August has long had a reputation for an abundance

of meteors. The Perseids have been referred to as the "tears of St.

Lawrence", since meteors seemed to be in abundance during the festival of

that saint on August 10th, but credit for the discovery of the shower's

annual appearance is given to QuÐ"©telet (Brussels), who, in 1835, reported

that there was a shower occurring in August that emanated from the

constellation Perseus.

The first observer to provide an hourly count for this shower was Eduard

Heis (MÐ"јnster), who found a maximum rate of 160 meteors per hour in 1839.

Observations by Heis and other observers around the world continued almost

annually thereafter, with maximum rates typically falling between 37 and

88 per hour through 1858. Interestingly, the rates jumped to between 78

and 102 in 1861, according to estimates by four different observers, and,

in 1863, three observers reported rates of 109 to 215 per hour. Although

rates were still somewhat high in 1864, generally "normal" rates persisted

throughout the remainder of the 19th-century.

Computations of the orbit of the Perseids between 1864 and 1866 by

Giovanni Virginio Schiaparelli (1835-1910) revealed a very strong

resemblance to periodic comet Swift-Tuttle (1862 III). This was the first

time a meteor shower had been positively identified with a comet and it

seems safe to speculate that the high Perseid rates of 1861-1863 were

directly due to the appearance of Swift-Tuttle, which has a period of

about 120 years. Multiple returns of the comet would be responsible for

the distribution of the meteors throughout the orbit, but meteors should

be denser in the region closest to the comet, so that meteor activity

should increase when the comet is near perihelion (as has been

demonstrated by the June BoÐ"¶tids, Draconids and Leonids).

As the 20th-century began, the maximum annual hourly rates of the Perseids

seemed to be declining. Although rates were above Denning's derived

average rate of 50 per hour during five years between 1901 and 1910, the

observed rate in 1911 was only 4 and for 1912 it was 12. Denning wondered

whether the shower was declining, but hourly rates seemed to return to

"normal" in the years that followed. Quite unexpectedly the shower

suddenly exploded in 1920, when rates were estimated to be as high as 200

per hour. This was extremely unusual as it came at a time when the parent

comet was nearing aphelion! Although a few weaker-than-normal years

occurred during the 1920's, the Perseids regained their consistency

thereafter, and, except for abnormally high rates of 160 and 189 during

1931 and 1945, respectively, nothing unusual was observed up through 1960.

During 1973, Brian G. Marsden predicted Comet Swift-Tuttle would arrive at

perihelion on September 16.9, 1981 (+/-1.0 years). This immediately

generated excitement among meteor observers as the potential for enhanced

activity unfolded. This excitement seems to have been