Palestinian Astronomical Society                      (PAS)

• Introduction to Leonids .
• Leonids in History .
• Temple Tuttle Comet .
• 1999 Storm .
• Leonids Observations .
• Leo Constellation .
• Dang. on Satellites:
• Leonids on the Moon .
• Leonids in the 21st centrury .
• Conference @ AUASS .
• Leonids Image Archive .
• Leonids Links .

Introduction

          The Leonids are a meteor shower that  appear to radiate out of the constellation Leo. A Meteor, also known as a "shooting star. All meteors appear as brief streaks of light moving a short distance across the sky. Some meteors move slow and some move fast. Here is a video of a bright, slow meteor. They enter Earth's atmosphere traveling at speeds of over 158,000 miles per hour (mph). A meteor that appears brighter than any of the stars and planets is called a fireball. The earth  experiences about a dozen major meteor showers every year, for example, every August we experience the Perseids,            every December we have the Geminids, and every November we have the Leonid meteor shower.. All meteor showers have been associated with the encounter of the Earth  with the debris cloud of a parent comet. The meteor flux associated with the Leonid shower, for example, is normally about 15 per hour. A Meteor storms are relatively rare, occurring once every few decades. They are the very enhanced meteor flux experienced  with the close passage of the parent comet. The most intense meteor storm on record is the Leonid meteor storm on  November 17, 1966, when the peak meteor flux reached about 150,000 per hour.Because of this the leonids are know as  the  King of the Meteor Showers .

        In the case of the Leonids the parent comet is named 55P/Tempel-Tuttle (click here for detailed info on this comet) and it makes an appearance in our skies every 33.25 years. Comets are composed of ice and dust. Every time a comet approaches the sun the ice melts and dust is released. Eventually the dust spreads completely around a comet's orbit, but most of the dust stays close to the comet. When Earth passes through the dense cloud of dust the result is a spectacular meteor shower or a meteor storm. Meteor storms produce several thousand meteors per hour.Since Tempel-Tuttle passed perihelion (closest point to the sun) on 28 Febuary 1998, the years 1998 and 1999 were expected to produce very strong displays. During 1998 the Leonids peaked over Europe with hourly rates of 250-300, while in 1999 astronomers are predicting an even better display over western Europe and the Atlantic .

        In mid-November 1999 Earth will take a plunge through an interplanetary river. The river is a river of dust, sparse and thin, composed of sand bits and dust clods  separated by miles of vacuum. For a few hours, many of these   particles will tear into the Earth's upper atmosphere at a speed  of 71 kilometers (44 miles) per second. Each will produce a  momentary streak of light in the sky, a shooting star of the  Leonid meteor shower.

         The Leonid shower happens every year with a  maximum hourly rate of 10-15 but this year should be quite a spectacle as the Earth passes through its tail soon after the comet has passed the Earth. During the years between the comets 33 year journey the earth passes through the remnants of the tail after it has long gone.

        The storm power is measured by ZHR (Zenithal Hourly Rate) which is the number of meteors that a single observer would see per hour if the sky were dark enough for 6.5-magnitude stars to be visible and the shower's radiant were at the zenith.

HISTORY

        The Leonids have been well-observed for over 1000 years. But strong interest in discovering the nature of meteor showers really did not begin until the great 1833 display of the Leonids. In the years following the 1833 display research increased and  several astronomers began looking for previous appearances of the Leonids and other meteor showers among ancient and medieval documents. A significant addition to our knowledge of the ancient and medieval Leonid displays came in 1958 when Susumu Imoto and Ichiro Hasegawa published a list of meteor shower accounts obtained from Chinese, Japanese, and Korean historical texts.
 
 

         Meteor Showers were neither known nor understood during the first half  of the 19th Century. Thus, when Americans awoke during the twilight  hours on November 17th, 1833, many thought Judgement Day had finally arrived.

Leonid Observations: 1833 to present

      The night of November 12-13, 1833, not only marks the discovery of the Leonid meteor shower, but sparked the actual
birth of meteor astronomy. During the hours following sunset on November 12, some astronomers noted an unusual number of
meteors in the sky, but it was the early morning hours of the 13th that left the greatest impression on the people of eastern
North America. During the 4 hours which preceded dawn, the skies were lit up by meteors.estimated that a thousand meteors a minute emanated from the region of Leo. Newspapers of the time reveal that almost no one was left unaware of the spectacle, for if  they were not awakened by the cries of excited neighbors, they were usually awakened by flashes of light cast into normally dark bedrooms by the fireballs.Finally, noting that an abnormal display of meteors had also been observed in Europe
and the Middle East during November 1832.
 

Images of  1833  Storm For More 1833 images Click Here

        One of the more significant findings of the 1833 Leonid storm was the determination of the meteor shower's radiant. This was the first time a shower radiant had ever been pinpointed more precisely than a simple direction in the sky or even a constellation.Next, in November 1834, the Leonids reappeared and, although they were not as plentiful as in the previous year, they did demonstrate that some annual activity might be present from this region. In the years that followed, Leonid displays continued to weaken. The1833 storm was clearly rich in fireballs.

The Leonids of 1866

          The expected meteor storm occurred in 1866 as predicted, with observers reporting hourly rates ranging from 2000 to
5000 per hour. The 1867 display had the misfortune of occurring with the moon above the horizon, but observers still reported
rates as high as 1000 per hour, meaning the shower may have actually been stronger than in the previous year. Another strong
appearance of the Leonids in 1868 reached an intensity of 1000 per hour in dark skies.

       The year 1867, marked an important development in the understanding of the evolution of the Leonids. On December
19, 1865, Ernst Wilhelm Liebrecht Tempel (Marseilles, France) had discovered a 6th-magnitude, circular object near Beta
Ursae Majoris. After an independent discovery was made by Horace Tuttle (Harvard College Observatory, Massachusetts) on
January 6, 1866, the comet took the name of Tempel-Tuttle. Perihelion came on January 12, 1866, afterwhich the comet
began fading so rapidly, that it was not seen after February 9. Orbital calculations shortly thereafter revealed the comet to be of
short period, and, as 1867 began, Theodor von Oppolzer had more precisely calculated the period to be 33.17 years.

The Leonids of 1899

       Numerous confident predictions were put forth that the Leonids would next be at their best in 1899, and an early sign of
returning enhanced activity was detected in 1898, when hourly rates reached 50-100 in the United States on November 14.
Predictions had been made and newspapers in Europe and America made the public well aware that astronomers were predicting a major meteor storm. Although the "storm" failed to appear, the Leonids did possess maximum hourly rates of 40 on November 14---at least indicating some unusual activity. Later investigations revealed the stream to have experienced close encounters with both Jupiter (1898) and Saturn (1870), so that the stream's distance from Earth in 1899 was nearly double that of the 1866 return.

The Leonids of 1932-1933

       The Leonids returned to normal in the years following 1903, with hourly rates ranging from 5 to 20 (average about 15).
Despite having miscalculated the Leonid maximum in 1899, astronomers began to make predictions for the next return---the
most likely date being 1932. Enhanced activity began early when, in 1928, maximum hourly rates reached 50 or more. During
1929, rates were lower, only 30 per hour, but moonlight was then a factor.

The Leonids 1966
 
 

Photos from the  1966 Storm

       Only one true meteor storm has occurred during the modern age of  easy astrophotography. On the morning of November 17, 1966, skywatchers in western North America  were spellbound by an awesome flood of faint and bright meteors around   12:00 Universal Time. The storm of 1966  favored small, faint meteors up to 50 meteors per second were seen for about an hour!  It seems that whenever 55P/Tempel-Tuttle is within a few hundred days of passing Earth's orbit, Leonid showers contain an above-average proportion of fireballs and bolides (bright meteors that flare or  explode).

         Comets are formed in the cold outer  reaches of the solar system. When, for some reason, the orbits are perturbed,  they come into the inner solar system, and in some cases, take paths which cross the orbit of the Earth.As the comet approaches the Sun, it begins to heat up, and the ice boils off, taking with it the rock and dust. This solid material follows roughly the same path as the comet. Hence, when the Earth later passes through the same region of space that the comet previously passed through, we encounter the debris cloud. The entry of the small pieces of rock into the Earth's atmosphere at high speeds causes them to burn up and in the process give off a flash of light. The flash of light is the meteor we see from the surface.

          Ernst Wilhelm Liebrecht Tempel discovered this comet on 1865 December 19. It was then in the evening sky near Beta Ursa Majoris. He described it as a circular object, with a central condensation and a tail 30 arcmin long. Horace Parnell Tuttle (Harvard College Observatory, Cambridge, Massachusetts) independently discovered this comet on 1866 January 6.
 

Right : Photo of the Tempel-Tuttle Comet when the comet was 0.98 AU from the sun and 1.22 AU from the Earth. A faint tail can be seen extending to the upper left  (the anti-solar direction ). The image shown here was obtained at the 42" Hall telescope at Lowell Observatory  by Tony Farnham

         The duration of this meteor shower covers the period of November 14-20. Maximum currently occurs on November 17
Although the maximum hourly rate typically reaches 10-15, this shower is most notable for producing greatly enhanced activity every 33 years---events that are associated with the periodic return of comet Tempel-Tuttle. During these exceptional returns, the Leonids have produced rates of up to several thousand meteors per hour.

 Above: The Leonid meteors and Earth orbit the Sun in nearly opposite directions, so they run into each other nearly head on. The meteoroid stream follows the orbit of periodic Comet 55P/Tempel-Tuttle, which is  inclined only 17° to the Earth's orbital plane. The line of nodes is where the planes of the two orbits intersect.

      Because of the gravitational influences of the planets, there has been a  steady advancement of the line of nodes of Tempel-Tuttle. This basically means that the  point where Earth intersects the comet's orbit occurs later every century. Therefore, the Leonids occurred in mid-October during the 10th century, late October during the 16th century, and mid-November during the 20th century.

      Every year on about November 17th Earth's orbit around the Sun carries us though the Leonid meteor stream. In ordinary   years we encounter little or nothing.

1999 Storm .

       In 1997 the ZHR remained as high as 80 for about 12 hours, though a bright waning gibbous Moon made this difficult to  determine.  In 1998, two peaks occurred. The first (and best looking) was about a day earlier than expected while the second peak was right on time with scientific predictions. The first peak had large meteor streaks (indicating larger dust particles) that were rather impressive. Studies have shown that this was the result of the dust trail created by the comet in 1899. The second peak was  caused by the dust trail from the 1966 passage of the comet. The 1899 dust trail consisted of larger particles (the smaller particles had time to disperse), which caused the larger meteor streaks.
 

Photos from the  1998 Shower

       On November 17 and 18, 1999, the earth will pass through the tail of comet Tempel-Tuttle.This year , scientists expect
a meteor storm  to occur , that is , a great meteor shower which produces thousands of meteors per hour.It is expected that the peak will occur on November 18, at 04:08 Local Palestinian Time (02:08 UT), and would show about 1500 meteors per hour by naked eyes. The peak will last about 2 hours and the radiant is at high elevation in Middle East.Models show that Earth will pass close to a trail of dust that was ejected in 1899, the same trail as responsible for the 1966 storms.The Middle  East is likely to experience the highest rates observable anywhere on the Earth in 1999.

Will a storm happen ?

        Will a storm happen this year ? Well, most scientists believe that there will be a storm but some believe that the storm will be in 2000 or 2001 .For example, it was expected that a Leonids' storm would occur in 1899, but a storm did not actually take place !! On the other hand, astronomers didn't expect a Leonids' storm in 1966, but a storm did occur, and about 200,000 - 1,000,000 meteors were seen by naked eyes, where it was the biggest storm ever recorded !! Some scientists expect that the peak ZHR in 2001 and 2002 are likely to be 10 to 20 times higher. The effect of the full moon in 2002 will probably make 2001 the best year for observed rates.

         A vote on leonids.com shows that around 79% of the people believe that the Leonids will be better than the last and 17% said that it will be worse and 4% said that it will be the same.

       The point from where the Leonid meteors appear to radiate is located within the constellation Leo and is referred to as
the radiant. The radiant is located in the western portion of that constellation in what is commonly referred to as the "sickle" or
"backwards question mark." The radiant rises around 12:30 a.m. local time. Although a few Leonids can be observed prior to
this, more will be seen after it rises. At about 3:00 a.m. the radiant is about 30 degrees above the horizon. The radiant location
with respect to the horizon is shown below:

      The number of meteors you see depends heavily on your light pollution, the altitude of the shower's radiant, the size of your unobstructed view, and other factors. While gazing and waiting, you'll have plenty of time to find the  limiting magnitude in the part of the sky you're watching -- the faintest star you can see with the naked eye

As always when meteor observing, you'll want warmer clothing than you would expect, a reclining lawn chair to lie back in      comfortably, and of course a reasonably dark location with an open sky view. By far the best way to take notes is to speak    into a tape recorder without taking your eyes off the sky, especially if meteors become frequent. Bring a watch that you      have set accurately, and insert the time into your notes at least  every half hour -- more frequently if rates change rapidly.
 If you miss the Leonids  this time around, don't count on another chance 33 years  hence. The years 1998 through 2000 are probably the last for  several more 33-year cycles when a Leonid storm is even  possible (S&T: November 1996, page 74). A perturbation by  Jupiter in 2029 will tug the comet's orbit away from Earth, and   not until 2098 or perhaps 2131 will hopes for a Leonid storm  again be justified.
No matter how the shower performs or where you're located, the best time to watch is from 1 or 2 a.m. local time until the
 first light of dawn. This is when Leo has risen above the horizon and is climbing high in the eastern sky. The shower's  apparent radiant point is within the Sickle of Leo at right  ascension 10h 14m, declination +22°. This isn't necessarily where to watch, however. The best direction to watch is simply the darkest part of the sky, perhaps 45° to 60° from the radiant if you have a choice. The important thing about the radiant is its height above the horizon. The higher the radiant, the more meteors will appear all over the sky.

     The Lion (also Great Lion, Leo major) is one of the constellations of the Zodiac. It comprises 77 stars that are visible to the 'unarmed' human eye.The brightest is Regulus (='Little King') at 85 light-years from Earth, the second brightest Denebola at 42 light-years. Eta Leonis, north from Regulus, looks weak, but  it spreads a hundred times as much light as Regulus. This star is at a much greater  distance from Earth: 1700 light-years. In the constellation of Lion and in its surroundings astronomers find a large number of  galaxies like M65 and M66. Both have a beautiful spiral-form. They are at a distance of 20 million light-years.  The constellation of Lion was already mentioned in the famous Almagest of the  Egyptian astronomer Ptolemaios. Copernicus gave Regulus its name during the Fifteenth Century. A second lion-constellation is Little Lion (Leo minor), introduced around 1670 by the German astronomer Hevelius. Leo Minor can be found between Great Lion and Great Bear. This constellation consists of 24 visible stars, but no particular bright ones.

Showers of Leo:

      There are a large number of meteor showers assiciated with this constellation. The most famous are the Leonids. This shower radiates from the region of gamma Leo and can be seen form November 14-20; the maximum can be observed on November 17th. Although the hourly rate from 10 to 15 meteor seems to be small there is a cyclus of about 33 years with an enhanced activity. Other Showers include:
The shower of the Alpha Leonids was first confirmed by Radio Meteor Project. The duration of this shower cover the period
from January 13th to February 13th.

From February 14th to April 25th the Beta Leonids are active. The maximum takes place around March 20th.
Nearly at the same time - from February 2nd to March 19th - the Delta Leonids can be observed. The maximum of the
activity peaks at February 22nd.

A rather weak shower are the Gamma Leonids, which are active from August 14th to September 12th with a maximum
occuring on August 25th.

The meteor shower of the Rho Leonids seems to be non-existent; yet it has been discovered by radio studies in the 1960's. It
seems to be "active" around March 14-15th.

The Sigma Leonids are another storm of doubt. Only one observation has been made.

          Meteors do not represent any real danger on Earth, since they are small grains of sand, generally in the range of 1 mm - 1 cm in diameter. All of which burn up, in fact, long before reaching the surface of Earth.The world's space  agencies are nervously awaiting possible strikes to the more than 650 working satellites that currently orbit Earth. Many  satellites, including the Hubble Space Telescope, will be  carefully rotated to present their least vulnerable profiles to the  potential sandblasting.

        This new awareness is important because our satellites, totaling more than 650 on orbit, form a vital infrastructure for communications, weather and climate monitoring, navigation, national defense, and astronomical research. When the last major meteoroid storm occurred in the mid 1960s when we had few satellites.

          When the Leonid meteor shower strikes on the morning of November 18, 1999, our planet won't be the only place in the cross hairs. The Moon will also pass very close to the debris stream of comet Tempel-Tuttle. Here on Earth, space-borne meteoroids will plummet into the atmosphere and burn up, creating streaks of light called meteors.The vast majority of

meteoroids will burn and disintegrate well before they hit the ground. The situation on the Moon, where there is no appreciable  atmosphere, is different. Every bit of comet debris that rains down on our satellite will hit its surface. Some meteor enthusiasts hope that will create a  different sort of display. Rather than streaks of light in lunar skies, there could be flashes of light on the Moon's surface each time a sizable meteoroid hits the ground.Last year, during the 1998 Leonid meteor shower, the phase of the moon was new. It was so close to the sun in the sky that observing faint lunar meteorite flashes was impossible. This year is different. During the 1999 Leonid shower the phase of the Moon will be just 2 days past first quarter. That means the moon will visible in the night sky during the early evening on November 17, and approximately 35% of the lunar disk as seen from Earth will not be illuminated by  sunlight. There will be plenty of dark lunar terrain where flashes might be visible. Watching meteorites fall on the moon ... is within reach of (modest) amateur  telescopes

Leonids in the 21st centrury

          Looking farther ahead, Brian G. Marsden and Gareth Williams  (Minor Planet Center) and Donald K. Yeomans (Jet Propulsion Laboratory) have calculated the comet's path through future  perturbations. They find that as Comet Tempel-Tuttle  approaches the Sun toward a May 2031 perihelion, it will pass within 1.5 a.u. of Jupiter in August 2029. This encounter will divert the comet to cross the Earth's orbital plane even farther inward. The distance from the comet's orbit to ours will increase to 0.0162 a.u., the largest separation since 1733.
        Something similar happened before the Leonid apparition of  1899. Comet Tempel-Tuttle made close approaches to Saturn in 1870 and Jupiter in 1898. As a consequence, its orbit was shifted to 0.0117 a.u. inside Earth's. Sure enough, the Leonids  in 1899 were conspicuous only by their absence.  There's little improvement at the following return in 2065; the     separation diminishes only slightly to 0.0146 a.u. Yeomans  notes that "it will be another century after the 1998-99 events      before significant Leonid meteor displays are once again likely."  Indeed, not until 2098, when the separation distance shrinks to  0.0062 a.u., or perhaps 2131, when for the first time since 1633 the comet crosses our orbital plane slightly outside the    Earth's orbit (at a distance of 0.0089 a.u.), will any hopes for a Leonid storm again be justified.

      The Arab Union for Astronomy & Space Sciences (AUASS), the Institute of Astronomy & Space Sciences, and the Jordanian Astronomical Society, organize the 1999 Jordanian Leonid Meteors Conference, 12-21 November 1999.Many scientists and astronomy amateurs had been invited to participate in the conference and in the astronomical camping in the Jordanian desert to observe this shower from many countries including:  Palestine , New Zealand , Northern Ireland , Australia, Netherlands , Germany , Australia ,  Iran, UAE , Syria , Singapore.

     The palestinian Astronomical Society (PAS) will send a representative to attend the Conference and the Camp .For more  information about the Conference  and the Camp please visit the website of the Jordanian Astronomical Society.

     Click Here to go to the leonids Image Archive

  Leonids Live!
  Leonids in the Crystal Ball
  International Meteor Organization
Meteor Observing Guide
  The Leonid Meteor Outburst of 1997
  Leonids on the Horizon
  Leonid Sample Return Update
  The Ghost of Fireballs Past
  The 1998 Leonids
  Leonids Sample Return payload recovered!
  Early birds catch the Leonids
  A high-altitude look at the Leonids
  The Leonid Sample Return Mission