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The Leonid Meteors

Royal Greenwich Observatory
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Short Special Information Leaflet No. 19: 'The Leonid meteors'

The Leonids:

One of the most prolific meteor showers is the Leonids. The radiant is in the constellation Leo and meteors from this shower can be seen over a period of about 2 days centred on approximately November 17.

This meteor stream is associated with Comet Tempel-Tuttle.
As the meteors in the stream are thought to be dust particles released from the comet, it is thought likely that there is a dense stream of such particles in the path of the comet and located close to it.

The Leonids have been seen to have very brief periods when hundreds of meteors can be seen. This does not happen every year but seems to come to a peak every 33 years, which is the period of Comet Tempel-Tuttle.
These storms of shooting stars were seen in 1799, 1833, 1866 and, most recently in 1966. The expected storms in 1899 and 1933 were very disappointing. The next peak should therefore occur in 1998 or 1999.

In 1995 observers in the UK saw a peak of activity at around 04:00 UT on November 18, equivalent to a 'zenith hourly rate' of about 40. In 1996 the Earth passed through the path of the comet at around 10:00 UT in the morning of November 17, but for observers in western Europe the best time to observe was after midnight on the night of November 16/17.
In 1997 the position of the Moon will not be favourable. At Full Moon on November 14th, it will interfere with late night observing.

The shooting stars should appear to come from within the 'sickle' of the constellation Leo, which rises around 23:00 local time.
The number of meteors might not be very high but predictions could be wrong and a peak might occur.
Leonids are typically extremely swift meteors and a notable portion leaves a persistent train.

The peak could well be only an hour long and the exact time of the Earth passing through the maximum is only poorly known and so it will be worth keeping a lookout from about midnight onwards, always assuming that the skies are clear!

For photography, the BAA recommend using a wide-angle lens at f/2.8 or faster, with a fast film such as Ilford HP5plus, pushed to 800 ISO. Mount the camera on a tripod and aim it in the direction of Ursa Major or Taurus.
Leave the shutter open for 10-15 minutes from a dark location. Bear in mind that only the brightest meteor tracks will be recorded but these should be seen against star trails resulting from the Earth's rotation. Remember to record the start and end times of your exposures and the sky conditions at the time.

Produced by the Information Services Department of the Royal Greenwich Observatory.

PJA Wed May 8 10:44:36 GMT 1996, revised MJP Nov 1996

webman@mail.ast.cam.ac.uk

ARVAL's Notes:

The Leonids should be active between November 14 to November 21, and they should peak at some 40+ meteors per hour.

The typical average velocity of the Leonids meteors is 71 Km/s.

Information from the 1997 Meteor Shower Calendar of the International Meteor Organisation (IMO)

The Leonids is a periodic meteor shower that tends to be insignificant most years, but at a 33 year intervals produces a spectacular meteor storm.
The shower radiant is R.A. 10h 12', Dec. +22°
It is associated with comet Tempel-Tuttle (1866 I).
The showers of 1799, 1833, and 1866 were rather like storms, but in 1899 and 1933 showed only mediocre displays. (1)

A year or two before the Leonid storms of 1833 and 1966, the comet barely grazed inside our orbit, at distances of 0.0012 and 0.0031 A.U. respectively. Hourly rates of roughly 50,000 to 150,000 meteors were seen in both cases.
For the 1998-1999 displays the distance increases to 0.0080 A.U. This is nearly three times as far as in 1966 and more than six times as far as in 1833. One might conclude that the 1998-99 displays could fall well short of the storm activity observed in 1833 and 1966.
Even though, there will be a consolation prize. Comet Tempel-Tuttle itself will have its best apparition since 1865. Donald K. Yeomans (JPL) notes that this historic object should pass closet to earth, 0.36 A.U., on January 17, 1998, when it will appear less than 8° from the north celestial pole. (2)

Sources:
(1) Facts on File Dictionary of Astronomy, edited by Valerie Illingworth.
(2) Sky & Telescope, November 1996, pg. 74.

The beginning of the scientific study of meteor showers is attributed to the spectacular display produced by the Leonids of 1833. It was discovered that the "Meteor showers" seem to originate from a position in the sky named the Radiant, so its meteoroids must move in parallel orbits, forming a "current". The radiant of the Leonids, is 10° North of Regulus, in the constellation of Leo (in R.A. 10h 12', Dec. +22°), thus its name.
The first corroborating report found was that from Alexander von Humboldt, in his book "Journey to the Equinoctial Regions of the New Continent" (1816), he reported to have observed with Aimé Bonpland, from Cumaná, in Venezuela, thousands of bright meteors before the dawn of November 12, 1799.
Humboldt's report on this observation started the investigation on the annual periodicity of meteor showers.

The night of November 11 to 12 was cool, and most beautiful. In the morning from 2 1/2 the most extraordinary luminous meteors were seen from the East. Mr. Bonpland, who had risen to enjoy the cool in the gallery perceived them first. Thousands of bolides and shooting stars followed during 4 hours. Their direction was very orderly from North to South, and they filled a part of the sky extending from true East, 30° towards the North and the South. In an amplitude of 60° the meteors were seen rising above the horizon to the E.N.E. and E., tracing arches more or less large and falling to the South after following the direction of the meridian. Some reached 40° of altitude: all surpassed 25° to 30°. The wind was very light in the lower regions of the atmosphere and came from the East. No traces of clouds were seen. Mr. Bonpland refers that from the start of the phenomenon there was no space in the sky equal in extension to three diameters of the moon that did not seem at each instant full of bolides and shooting stars. The former in lesser numbers; but as they were of different magnitude, it was impossible to fix the limit between these two classes of phenomena. All these meteors left luminous traces from 8 to 10 degrees of length, as it often occurs in the equinoctial regions. The phosphorescence of these traces or luminous bands lasted from 7 to 8 seconds. Some shooting stars had a distinct nucleus, as big as the disk of Jupiter, from which very bright sparks shot. The bolides seemed to break as if from the explosion; but the thickest, from 1° to 1° 15' in diameter, disappeared without scintillation, leaving behind them phosphorescent traces, of a width which exceeded from 15 to 20 minutes. The light from these meteors was white and not reddish, which must be attributed with no doubt to the lack of vapors and the extreme transparency of the air. By the same cause in the tropics the stars of first magnitude show when they raise a light sensibly more white than in Europe.

Almost all the inhabitants of Cumaná were witnesses of this phenomenon, because they left their houses before 4 to attend the first mass of the morning. .....

From four the phenomenon diminished slowly; The bolides and shooting stars became rarer, although some were distinguished towards the Northeast, by their whitish fulgor and the speed of their movement, one quarter of an hour after the sunrise.

Alejandro de Humboldt, Viaje a las Regiones Equinocciales del Nuevo Continente. Book IV. Chapter X.
Spanish translation of Lisandro Alvarado.
Monte Ávila Editores, 2^nd edition, 1991. Tome II.

Updated: July 21 '07, June 24 '14

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