What Henry Dowling and many persons the world over witnessed in November of 1833 has repeated itself many, many times on or about November 16-18 each year.
Indeed, we know that this 1833 spectacle was not the first time that this heaven-sent fireworks display has appeared -- and certainly was not the last. Today we know this incredible celestial light show as the Leonid meteors, from the sky direction (constellation of Leo) at which they appear to originate.
The Earth in its annual path about the sun intersects the great cloud of celestial debris each November. It is just one of about a dozen major "meteor showers" that light up our skies each year. But the Leonids can be far more active in some years than in others.
For 2001 -- 168 years after the spectacular "Night the Stars Fell" over North America -- many astronomers are predicting that once again the skies might be filled with an incredible display similar to that of 1833. One fact is certain: The Leonids meteors WILL be seen in November -- but how many will be seen?
You would be better off betting on a horse race than predicting the "hourly number" of Leonid meteors that you might expect to see in 2001. But many astronomers are going out on a limb on this one, predicting this to be finest meteor display in 35 years, and some even suggesting a show rivaled only by that one in 1833.
If it does happen, we can expect the light show to begin on the evening of Saturday, November 17 and last into the following predawn skies of Sunday, November 18 for most of North America. Rarely do we see the incredible number of meteors witnessed in 1833; indeed most skilled observers feel fortunate if a dozen or so bright meteors are seen hourly during any meteor shower's peak.
Could it be that 2,500 per hour might be seen this year? That is a "conservative" number that some experts are predicting for this year's Leonids, and for those in the far west Pacific, perhaps twice that many will be visible.
So, before we look to a preparing ourselves for this optimistic Leonid Meteor Shower forecast, let us examine the "meteor phenomenon" and prepare ourselves as better observers for the 2001 event!
Today we know this phenomenon of "shooting stars" as that of a common meteor that collides at high rates of speed into the Earth's atmosphere. There is much confusion when ever astronomically-educated persons talk about and describe the phenomena of the meteor, meteoroid and meteorite....all three start the same way, but end up differently.
Confusion or not, one thing is for sure: stars do NOT fall from the sky, and neither do "meteors." It just so happens that the Earth and the particles that create the meteor phenomenon are both moving in space and occasionally will run into each other. Following is a quick primer on this wonderful celestial event:
METEOROID: A small, usually grain-sized up to the size of perhaps a grapefruit, particle that is traveling in space; many times the meteoroid is moving with a huge group of particles, known as a "meteoroid cloud"; a meteoroid has NO LIGHT intrinsically, and is typically too small to reflect light as we see from larger bodies such as the Moon and planets. Thus, they normally are not seen except when colliding with the Earth's air.
METEOR: This is what we SEE when a meteoroid plunges into the Earth's atmosphere, the fiery result of friction from the small mass of the meteoroid passing at extremely high speeds into the air; as the meteor passes deeper (closer to the surface) into the Earth's air which becomes increasingly thicker toward ground, the friction increases. This can result in: a) the meteor getting brighter; b) the meteor changing colors; c) the meteor breaking apart (a "bolide" - see the photograph following); and/or d) the meteor burning out altogether.
Rarely do any meteors reach the ground. Typically those that do fall to Earth actually "catch up" with the Earth in its orbit after midnight local time, coming in from a direction opposite that which the Earth is moving. This results in greatly diminished speeds which prevents total vaporizing, and even some stones that strike the Earth still covered in ice!
METEORITE: These are any of those "meteors" that caught up with the Earth's motion, entered the atmosphere at a slower rate of speed (usually), and survived the fiery entry and friction to impact on the Earth's surface. Meteorite finds are extremely rare and many happen during daylight hours. Interestingly, nearly every bright meteor that you might see during the Leonid meteor shower this year might "appear to have fallen just over that hill" and hit the Earth when in fact it was skimming through the air, many times actually bouncing off of it, as a rock "skips" across a very still pond.
There are two types of meteoroids/meteors/meteorites: stony, which are just as their name implies, rich with common molecular substances much like stones on Earth; and, iron, which are considerably more dense and packed with atoms of metallic elements. Regardless of type, the meteorites that are found on Earth are all extremely dense and one the size of a lemon can weight many pounds! A meteorite spanning about four feet diameter would weigh hundreds of pounds.
As the meteoroid enters the atmosphere it is typically traveling an incredible 40 to 50 miles per second. This remarkable speed and collision of the meteoroid particle with our air causes both the meteor and the air around it to glow. The Leonid meteors are among the fastest entering the atmosphere of all meteors, since they hit the Earth almost head-on in its path around the sun. Thus, few Leonids have been known to fall as meteorites upon the ground. Most burn and vaporize before reaching anywhere close to the Earth's surface.
All larger meteors -- roughly larger than the size of a grapefruit before entering the atmosphere -- are capable of reaching the ground. In addition, rapid-moving meteors can create a "sonic boom" from the rapid compression of air ahead of the plunging object. Thus, many brighter and lower-altitude meteors can frequently be witnessed with sound in addition to light.
Most meteors last only 2-3 seconds as they streak rapidly across the sky, yet there were many instances with the 1999 Leonids of the meteor "train", or fiery wake, lasting as long as several minutes as they linger high in the stratosphere, a layer so high that it is virtually unaffected by winds common to the lower troposphere. Newspaper accounts of the 1833 Leonids suggest that many smoky trains persisted for as long as 20 minutes.
Next Up: Part 3 -- The History of the Leonid Meteor Storm
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