Leonids - AbsoluteAstronomy.com

The Leonids (ˈliːənɪdz ) is a prolific 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...

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...

Tempel-Tuttle

55P/Tempel-Tuttle

55P/Tempel–Tuttle is a comet that was independently discovered by Ernst Tempel on December 19, 1865 and by Horace Parnell Tuttle on January 6, 1866.It is the parent body of the Leonid meteor shower...

. The Leonids get their name from the location of their 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....

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....

Leo

Leo (constellation)

Leo is one of the constellations of the zodiac. Its name is Latin for lion. Its symbol is . Leo lies between dim Cancer to the west and Virgo to the east.-Stars:...

: the meteors appear to radiate from that point in the sky

Sky

The sky is the part of the atmosphere or outer space visible from the surface of any astronomical object. It is difficult to define precisely for several reasons. During daylight, the sky of Earth has the appearance of a pale blue surface because the air scatters the sunlight. The sky is sometimes...

. They tend to peak in November.

Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

moves through the meteoroid stream of particles left from the passages of a comet

Comet

. The stream comprises solid particles, known as meteoroid

Meteoroid

A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...

s, ejected by the comet as its frozen gases evaporate under the heat of the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

when it is close enough – typically closer than Jupiter's orbit. The Leonids are a fast moving stream which come close to or cross the path of the Earth and impact the Earth at 72 km/s. Leonids in particular are well known for having bright 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 or fireballs which may be across and have of mass and punch into the atmosphere with the kinetic energy

Kinetic energy

The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

of a car hitting at . An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet. Sometimes these trails of meteoroids cause meteor showers and sometimes meteor storms.

The meteoroids left by the comet are organized in trails in orbits similar to though different from that of the comet. They are differentially disturbed by the planets, in particular Jupiter

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

and to a lesser extent by radiation pressure

Radiation pressure

Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...

from the sun, the Poynting–Robertson effect, and the Yarkovsky effect

Yarkovsky effect

The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum...

. Old trails are spatially not dense and compose the meteor shower with a few meteors per minute. In the case of the Leonids, that tends to peak around November 17, but some are spread through several days on either side and the specific peak changing every year. Conversely, young trails are spatially very dense and the cause of meteor storms when the Earth enters one. Usual counts during a storm exceed 1000 meteors per hour, to be compared to the annual background (1 to 2 meteors per hour) and the shower background (a few per hour).

1800s

The Leonids are famous because their meteor showers, or storms, can be, and have been in a few cases, among the most spectacular. Because of the superlative storm of 1833 and the recent developments in scientific thought of the time (see for example the identification of Halley's Comet) the Leonids have had a major effect on the development of the scientific study of meteors which had previously been thought to be atmospheric phenomena. The meteor storm of 1833 was of truly superlative strength. One estimate is over one hundred thousand meteors an hour, but another, done as the storm abated, estimated in excess of two hundred thousand meteors an hour over the entire region of North America east of the Rocky Mountains. It was marked by the Native Americans

Native Americans in the United States

Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...

, slaves like Harriet Tubman

Harriet Tubman

Harriet Tubman Harriet Tubman Harriet Tubman (born Araminta Harriet Ross; (1820 – 1913) was an African-American abolitionist, humanitarian, and Union spy during the American Civil War. After escaping from slavery, into which she was born, she made thirteen missions to rescue more than 70 slaves...

and slave-owners and others. Near Independence, Missouri

Independence, Missouri

Independence is the fourth largest city in the U.S. state of Missouri, and is contained within the counties of Jackson and Clay. It is part of the Kansas City Metropolitan Area...

, it was taken as a sign to push the growing Mormon

Mormon

The term Mormon most commonly denotes an adherent, practitioner, follower, or constituent of Mormonism, which is the largest branch of the Latter Day Saint movement in restorationist Christianity...

community out of the area. The leader of the Mormon

Mormon

The term Mormon most commonly denotes an adherent, practitioner, follower, or constituent of Mormonism, which is the largest branch of the Latter Day Saint movement in restorationist Christianity...

community, Joseph Smith

Joseph Smith

Joseph Smith was founder of what later became known as the Latter Day Saint movement or Mormons.Joseph Smith may also refer to:-Latter Day Saints:* Joseph Smith, Sr. , father of Joseph Smith...

, noted in his journal that this event was a literal fullfillment of the word of God and a sure sign that the coming of Christ is close at hand. Denison Olmsted

Denison Olmsted

Denison Olmsted , U.S. physicist and astronomer, was born at East Hartford, Connecticut. Professor Olmsted is credited with giving birth to meteor science after the 1833 Leonid meteor shower over North America spurred him to study this phenomenon.-Biography:In 1813, he graduated from Yale...

explained the event most accurately. After spending the last weeks of 1833 collecting information he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, and January 1836. He noted the shower was of short duration and was not seen in Europe, and that the meteors radiated from a point in the constellation of Leo and he speculated the meteors had originated from a cloud of particles in space. Accounts of the 1866 repeat of the Leonids counted hundreds per minute/a few thousand per hr in Europe. The Leonids were again seen in 1867, when moonlight reduced the rates to 1000 per hour. Another strong appearance of the Leonids in 1868 reached an intensity of 1000 per hour in dark skies. It was in 1866–67 that information on Comet Tempel-Tuttle was gathered pointing it out as the source of the meteor shower. When the storms failed to return in 1899, it was generally thought that the dust had moved on and storms were a thing of the past.

1900s

Then, in 1966 a spectacular storm was seen over the Americas. Historical notes were gathered thus noting the Leonids back to 900AD. Radar studies showed the 1966 storm included a relatively high percentage of smaller particles while 1965's lower activity had a much higher proportion of larger particles. In 1981 Donald K. Yeomans of the Jet Propulsion Laboratory reviewed the history of meteor showers for the Leonids and the history of the dynamic orbit of Comet Tempel-Tuttle. A graph from it was adapted and re-published in Sky and Telescope from Comet 55P/Tempel-Tuttle and the Leonid Meteors(1996, see p. 6.) It showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. This showed that the meteoroids are mostly behind and outside the path of the comet, but paths of the Earth through the cloud of particles resulting in powerful storms were very near paths of nearly no activity. But overall the 1998 Leonids were in a favorable position so interest was rising. Leading up to the 1998 return, an airborne observing campaign was organized to mobilize modern observing techniques by Peter Jenniskens

Peter Jenniskens

Petrus Matheus Marie Jenniskens is a Dutch astronomer and a senior research scientist at the Carl Sagan Center of the SETI Institute and at NASA Ames Research Center. He is an expert on meteor showers. Jenniskens is the author of the 790 page book "Meteor Showers and their Parent Comets"...

at NASA Ames Research Center. There were also efforts to observe impacts of meteoroids, as an example of transient lunar phenomenon

Transient lunar phenomenon

A transient lunar phenomenon , or lunar transient phenomenon , is a short-lived light, color, or change in appearance on the lunar surface....

, on the Moon in 1999. A particular reason to observe the Moon is that our vantage from a location on Earth sees only meteors coming into the atmosphere relatively close to us while impacts on the Moon would be visible from across the Moon in a single view. A sodium tail of the Moon

Sodium tail of the Moon

The Moon has been shown to have a "tail" of sodium ions too faint to be detected by the human eye. It is hundreds of thousands of miles long, and was discovered in 1998 as a result of Boston University scientists observing the Leonid meteor storm...

tripled just after the 1998 Leonid shower which was composed of larger meteoroids (which in the case of the Earth was witnessed as fireballs.) However in 1999 the sodium tail of the Moon did not change from the Leonid impacts. Research by Kondrat'eva, Reznikov and colleagues at Kazan University had shown how meteor storms could be accurately predicted but for some years the worldwide meteor community remained largely unaware of these results. The work of David J. Asher

David J. Asher

David J. Asher is a British astronomer, who works at the Armagh Observatory in Northern Ireland.He is known for the meteor research that he conducts with Robert McNaught. In 1999 and 2000, they accurately gauged when the Leonids meteor shower would peak, while underestimating the peak...

, Armagh Observatory

Armagh Observatory

Armagh Observatory is a modern astronomical research institute with a rich heritage, based in Armagh, Northern Ireland. Around 25 astronomers are actively studying stellar astrophysics, the Sun, Solar System astronomy, and the Earth's climate....

and Robert H. McNaught

Robert H. McNaught

Robert H. McNaught is a Scottish-Australian astronomer at the Research School of Astronomy and Astrophysics of the Australian National University. He has collaborated with David J. Asher of the Armagh Observatory....

, Siding Spring Observatory

Siding Spring Observatory

Siding Spring Observatory near Coonabarabran, New South Wales, Australia, part of the Research School of Astronomy & Astrophysics at the Australian National University , incorporates the Anglo-Australian Telescope along with a collection of other telescopes owned by the Australian National...

and independently by Esko Lyytinen in 1999, following on from the Kazan research, is considered by most meteor experts as the breakthrough in modern analysis of meteor storms. Whereas previously it was hazardous to guess if there would be a storm or little activity, the predictions of Asher and McNaught timed bursts in activity down to ten minutes by narrowing down the clouds of particles to individual streams from each passage of the comet, and their trajectories amended by subsequent passage near planets. However, whether a specific meteoroid trail will be primarily composed of small or large particles, and thus the relative brightness of the meteors, was not understood. But McNaught did extend the work to examine the placement of the Moon with trails and saw a large chance of a storm impacting in 1999 from a trail while there were less direct impacts from trails in 2000 and 2001 (successive contact with trails through 2006 showed no hits.)

2000s

Viewing campaigns resulted in spectacular footage from the 1999, 2001 and 2002, storms producing up to 3,000 Leonid meteors per hour. Predictions for the Moon's Leonid impacts also noted that in 2000 the side of the Moon facing the stream was away from the Earth but that impacts should be in number enough to raise a cloud of particles kicked off the Moon by impacts would cause a detectable increase in the sodium tail of the Moon. Research using the explanation of meteor trails/streams have explained the storms of the past. The 1833 storm was not due to the recent passage of the comet, but from a direct impact with the previous 1800 dust trail. The meteoroids from the 1733 passage of Comet Tempel-Tuttle resulted in the 1866 storm and the 1966 storm was from the 1899 passage of the comet. The double spikes in Leonid activity in 2001 and in 2002 were due to the passage of the comet's dust ejected in 1767 and 1866. This ground breaking work was soon applied to other meteor showers – for example the 2004 June Bootids

June Bootids

The June Bootids are a meteor shower occurring roughly between 26 June and 2 July each year. In most years their activity is weak, with a zenith hourly rate of only 1 or 2. However, occasional outbursts have been seen, with the outburst of 1916 drawing attention to the previously unknown meteor...

. Peter Jenniskens has published predictions for the next 50 years. However, a close encounter with Jupiter

Jupiter

is expected to perturb the comet's path, and many streams, making storms of historic magnitude unlikely for many decades. Recent work tries to take into account the roles of differences in parent bodies and the specifics of their orbits, ejection velocities off the solid mass of the core of a comet, radiation pressure

Radiation pressure

Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...

from the sun, the Poynting–Robertson effect, and the Yarkovsky effect

Yarkovsky effect

The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum...

on the particles of different sizes and rates of rotation to explain differences between meteor showers in terms of being predominantly fireballs or small meteors.

Year	Leonids active between	Peak of shower
2008	November 14 and 22	Nov. 17, 2008
2009	November 10 and 21	ZHR_max 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... ranging from 100 to over 500 on Nov 17th. The peak was observed at predicted time. The ZHR_max was 79
2010	November 10 and 21	ZHR_max ??

"There are no guarantees in meteor work ... observers should be alert as often as conditions allow throughout the shower, in case something unexpected happens."

External links

Worldwide viewing times for the 2011 Leonids meteor shower
Leonid dust trails by David Asher
The Discovery of the Perseid Meteors (after the Leonids and) Prior to 1837, nobody realized the Perseids were an annual event, by Mark Littmann
Lunar Leonids: Encounters of the Moon with Leonid dust trails by Robert H. McNaught
Brilliant Leonid storm likely fodder for later Lincoln speech by Jim Vertuno
NASA: Background facts on meteors and meteor showers
NASA: Estimate the best viewing times for your part of the world
Science@NASA: Leonids 2006
How to hear the Leonid Meteor Shower
Observatorio ARVAL – The Leonid Meteors
Animation of the Leonid Meteor Shower at shadow&substance.com
Leonids at The Big Blog Theory

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

1800s

1900s

2000s

See also

External links