Perseids
Encyclopedia
The Perseids are a prolific meteor shower
associated with the comet
Swift-Tuttle. The Perseids are so-called because the point from which they appear to come, called the radiant
, lies in the constellation
Perseus
. The name derives in part from the word Perseides
(Περσείδες), a term found in Greek mythology referring to the sons of Perseus. 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 130-year orbit. Most of the dust in the cloud today is around a thousand years old. However, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1862. The rate of meteor
s originating from this filament is much higher than for the older part of the stream.
The Perseid meteor shower
has been observed for about 2000 years, with the earliest information on this meteor shower coming from the Far East. Some Catholics refer to the Perseids as the "tears of St. Lawrence", since 10 August is the date of that saint's martyrdom.
The shower is visible from mid-July each year, with the peak in activity being between August 9 and 14, 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, but because of the path of Swift-Tuttle's orbit, Perseids are primarily visible in the northern hemisphere
. As with all meteor showers, the rate is greatest in the pre-dawn hours, since the side of the Earth nearest to turning into the sun scoops up more meteors as the Earth moves through space. In 2009, the estimated peak Zenithal Hourly Rate
was 173, but fainter meteors were washed out by a waning gibbous moon.
Meteor shower
A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller...
associated with the comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
Swift-Tuttle. The Perseids are so-called because the point from which they appear to come, called the radiant
Radiant (meteor shower)
The radiant or apparent radiant of a meteor shower is the point in the sky, from which meteors appear to originate. The Perseids, for example, are meteors which appear to come from a point within the constellation of Perseus....
, lies in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Perseus
Perseus (constellation)
Perseus is a constellation in the northern sky, named after the Greek hero Perseus. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations defined by the International Astronomical Union...
. The name derives in part from the word Perseides
Perseides
In Greek mythology the Perseides, "those born of Perseus" and Andromeda, are the members of the House of Perseus, descended, according to Valerius Flaccus through Perse and Perses...
(Περσείδες), a term found in Greek mythology referring to the sons of Perseus. 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 130-year orbit. Most of the dust in the cloud today is around a thousand years old. However, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1862. The rate of meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
s originating from this filament is much higher than for the older part of the stream.
The Perseid meteor shower
Meteor shower
A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller...
has been observed for about 2000 years, with the earliest information on this meteor shower coming from the Far East. Some Catholics refer to the Perseids as the "tears of St. Lawrence", since 10 August is the date of that saint's martyrdom.
The shower is visible from mid-July each year, with the peak in activity being between August 9 and 14, 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, but because of the path of Swift-Tuttle's orbit, Perseids are primarily visible in the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
. As with all meteor showers, the rate is greatest in the pre-dawn hours, since the side of the Earth nearest to turning into the sun scoops up more meteors as the Earth moves through space. In 2009, the estimated peak Zenithal Hourly Rate
Zenithal Hourly Rate
In astronomy, the Zenithal Hourly Rate of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky if the radiant of the shower were at the zenith...
was 173, but fainter meteors were washed out by a waning gibbous moon.
| Year | Perseids active between | Peak of shower |
|---|---|---|
| 2011 | July 17 - August 24 | August 13 (ZHRmax Zenithal Hourly Rate In astronomy, the Zenithal Hourly Rate of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky if the radiant of the shower were at the zenith... 100) |
| 2010 | July 23 – August 24 | August 12 (ZHRmax Zenithal Hourly Rate In astronomy, the Zenithal Hourly Rate of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky if the radiant of the shower were at the zenith... 142) |
| 2009 | July 14 – August 24 | August 13 (ZHRmax Zenithal Hourly Rate In astronomy, the Zenithal Hourly Rate of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky if the radiant of the shower were at the zenith... 173) |
| 2008 | July 25 – August 24 | August 13 (ZHRmax Zenithal Hourly Rate In astronomy, the Zenithal Hourly Rate of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky if the radiant of the shower were at the zenith... 116) |
| 2007 | July 19 – December 25 | August 13 (ZHRmax Zenithal Hourly Rate In astronomy, the Zenithal Hourly Rate of a meteor shower is the number of meteors a single observer would see in one hour under a clear, dark sky if the radiant of the shower were at the zenith... 93) |
| 1972 | August 12: reported to be the most active shower in recorded history |