High Rates Of 60 Meteors Per Hour example essay topic

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 Qu'e 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 (M"u nster), 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 Virginia Schiaparelli (1835-1910) revealed a very strong resemblance to periodic comet Swift-Tuttle (1862 ).

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 Bo " otis, Draco nids and Leonid's). 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 fully justified, as the average rate of 65 per hour during 1966-1975 suddenly jumped to over 90 per hour during 1976-1983 -- -with the high being 187 in the latter year.

Although meteor observers seemed content with their observations of the enhanced activity from Swift-Tuttle, comet observers were less enthusiastic as the comet was never recovered. Since the 1983 peak, hourly rates for the Perseids declined. With a full moon occurring just a day before maximum in 1984, the Dutch Meteor Society still reported unexpectedly high rates of 60 meteors per hour. In 1985, reported rates generally fell between 40 and 60 meteors per hour in dark skies, and results were generally the same in 1986. As the 1990's dawned, Marsden published a new prediction. If P / Swift-Tuttle was actually the same comet seen by Kegler in 1737, then the comet might pass perihelion during December 1992.

The comet was recovered late in the summer of 1992. Although not one of the most spectacular apparitions, the comet was well observed. But meteor observers were waiting for the Perseid display of 1993. Predictions indicated Europe was the place to be during the Perseid maximum of 1993. Observers from around the world flocked into central Europe and were met with hourly rates of 200 to 500. High rates were still present during 1994, this time with the peak occurring over the United States.

From the 1860's onward, studies of the Perseids began to include more than just hourly rates. Numerous observers began to plot the paths of meteors onto star charts to derive the points from which the meteors seemed to be radiating. The most prolific observer of this stream was William F. Denning, who, between 1869 and 1898, observed 2409 Perseids and became the first person to derive a daily ephemeris of the radiant's movement.