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Posts Tagged ‘Leonids’

The most visible meteor shower in most years are the Perseids, which peak on August 12 of each year at over 1 meteor a minute. A useful tool to calculate how many meteors per hour are visible from your observing location is found here: http://leonid.arc.nasa.gov/estimator.html.

APOD: 2004 August 13 - Perseid Fireball Over Japan

 

The most spectacular meteor shower is probably the Leonids, the King of Meteor Showers which peaks on a day near 17 November. Approximately every 33 years the Leonid shower produces a “meteor storm”, peaking at rates of thousands of meteors per hour. These Leonid storms gave birth to the term “meteor shower”, when it was first realised during the November 1833 storm that the meteors radiated from near the star Gamma Leonis. The last Leonid storms were in 1999, 2001 (two), and 2002 (two). Before that, there were storms in 1767, 1799, 1833, 1866, 1867, and 1966. When the Leonid shower is not storming it is less active than the Perseids.

APOD: November 13, 1998 - A Leonid Fireball From 1966

Other notable strog meteor showers are Quadrantids and  Geminids.

The Geminids are a meteor shower caused by an object named 3200 Phaethon, which is thought to be an extinct comet. The meteors from this shower can be seen in mid-December and usually peak around 12-14 of the month. The Geminid shower is thought to be intensifying every year and recent showers have seen 120-160 meteors per hour under optimal conditions. The Geminids were first observed only 150 years ago, much more recently than other showers such as the Perseids and Leonids.

APOD: 2004 December 22 - Comet, Meteor, Nebula, Star

The meteors in this shower appear to come from a radiant in the constellation Gemini (hence the shower’s name). However, they can appear almost anywhere in the night sky, and often appear yellowish in hue. The meteors travel at medium speed in relation to other showers, at about 22 miles per second, making them fairly easy to spot. The Geminids are now considered by many to be the most consistent and active annual shower.

The radiant f the Quadrantids is an area inside the constellation Boötes. The name comes from Quadrans Muralis, an obsolete constellation that is now part of Boötes. It lies between the end of the handle of the Big Dipper and the quadrilateral of stars marking the head of the constellation Draco. Adolphe Quetelet of Brussels Observatory discovered the shower in the 1830s, and shortly afterward it was noted by several other astronomers in Europe and America.

 

APOD: 2009 January 5 - Comet and Meteor

Peak intensity is exceedingly sharp: meteor rates exceed one-half of their highest value for only about 8 hours (compared to two days for the August Perseids). This means that the stream of particles that produces this shower is narrow – and apparently derived within the last 500-years from some orbiting body. The parent body of the Quadrantids was recently tentatively identified (in a paper by Peter Jenniskens) as the minor planet 2003 EH1, which in turn may be the same object as the comet C/1490 Y1 [2] which was observed by Chinese, Japanese and Korean astronomers 500 years ago. The best date to view the Quadrantids is January 3, although they can normally be viewed on any day from the 1st to the 5th of the month. The radiant rises after local midnight.

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Leonids 2009

The Leonids 2009 meteor shower did not show any sort of storm or outburst. It was rather a normal meteor shower witha  peak activity about 100 (comparable to Perseids). Well, we might have to wait quite a bit, say 20 years to the next expected outburst. The following plots are from IMO webpage, showing the zenith hourly rate.

The graph below shows the ZHR (Zenithal Hourly Rate), which is the number of meteors an observer would see under a very dark sky with the radiant of the shower in zenith.


ZHRmax = 88 based on 894 Leonids reported in 341 intervals, assuming population index r = 2.3

Peak of the Leonids activity, 2009

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A meteor is the visible streak of light that occurs when a meteoroid enters the Earth’s atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km. Millions of meteors occur in the Earth’s atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble. They become visible between about 40 and 75 miles (65 and 120 kilometers) above the earth. They disintegrate at altitudes of 50 to 95 km. 

For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres) the visibility is due to the air friction that heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles. The gases include vaporized meteoroid material and atmospheric gases that heat up when the meteoroid passes through the atmosphere. Most meteors glow for about a second. A relatively small percentage of meteoroids hit the Earth’s atmosphere and then pass out again: these are termed Earth-grazing fireballs.

Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as “random” or “sporadic” meteors, not associated with a specific single cause. In an active meteor shower like Perseids, almost one meteor can be observed per minute during the peak time.

 

APOD: 2008 January 3 - Geminids in 2007. It seems that all of the meteors are coming from a single point, the radiants.

The radiant or apparent radiant of a meteor shower is the point in the sky, from which (to a planetary observer) meteors appear to originate. The Perseids, for example, are meteors which appear to come from a point within the constellation of Perseus. An observer might see such a meteor anywhere in the sky but the direction of motion, when traced back, will point to the radiant. A meteor that does not point back to the known radiant for a given shower is known as a sporadic and is not considered part of that shower.



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Leonids meteor shower

Tonight is the peak of the Lenoids meteor shower. The Leonids are a prolific meteor shower associated with the comet Tempel-Tuttle.

Leonids have a normal (broad) component of dust particles along with filaments of newly ejected particles (by newly ejected, I mean in recent passages of the comet around the Sun). Each such filament contains a very sharp and  high density meteor sample. Hence, the duration of the shower is rather short, but the population of the bright meteors was reported to be high in last ten years.

Engraving of 1833 meteor storm

The enormous number of falling stars is called a storm. Such storms have been observed in 1833, 1866, 1867, and 1966. In 1998 return, an airborne observing campaign was organized at NASA Ames Research Center. This resulted in spectacular footage from the 1999, 2001 and 2002 storms producing up to 3,000 Leonid meteors per hour.

The predicted  ZHR for this year is about 300-400.  Good luck !

A photo of Leonids 2001.

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