Rates of several thousand meteors per hour are forecast for two predicted peaks in this years Leonid meteor shower early Nov. 19. But you wont see most of them. Even if you are blessed with excellent weather conditions, little or no artificial lighting and a wide-open view of the sky, a brilliant Moon will cut significantly into the potential number of meteors that you might otherwise spot.

A good analogy would be to think of the Moon as the equivalent of someone shining a giant spotlight down on your observing site. The actual number of meteors that you may count at the peak of this years display might only be about 5 to 25 percent of what you otherwise would have seen without that lunar interference.

We should anticipate a fair number of eye-catching fireballs (unusually bright meteors) and bolides (exploding meteors) this year. Thats because we were treated to many such meteors at last years Leonid display and for this year the Earth will again be passing through the same two trails of debris from comet Tempel-Tuttle that were encountered in 2001.

Some of the meteoroids that Earth encountered last year were probably somewhat larger than the usual dust and sand-grain sized particles. A few, in fact, may even have been as large as pebbles or marbles. Thats what makes the brighter shooting stars. Smashing into our atmosphere at some 44 miles per second, such pieces are capable of creating a brilliant splash in the sky.

Some meteors were so bright last year that they were readily visible in bright morning twilight and even daylight!

For select locations, perhaps the very best Leonids will come not during the predawn morning hours when the constellation of Leo is high in the sky, but rather during the late evening hours when the radiant is only just beginning to emerge above the horizon. The radiant is the point in the sky from which a showers meteors appear to emanate.

Normally, low-hanging radiants are bad news because they make shooting stars hard to see many simply shoot below the horizon -- but this is also the time when you might catch sight of an unusually beautiful type of meteor called an earthgrazer, sometimes called an earthskimmer.

Earthgrazers are long, bright shooting stars that can appear to streak from a point near or just below the horizon and embark on long, majestic paths that in some cases take them more than halfway across the sky. They sometime display colorful halos and long lasting trails.

Earthgrazers are so distinctive primarily because they follow a path nearly parallel to our atmosphere.

Earthgrazers may also be observable across parts of northern Canada where the Leonid radiant will lie close to the horizon, but unfortunately the radiant will be too far below the horizon for the rest of North America. Conversely, across much of Europe and western Africa, the Leonid radiant will be high in the sky, so as to preclude visibility of any Earthgrazers.

Hawaiian observers might be able to spot Earthgrazers around 12:35 a.m. Hawaiian Standard Time on Tuesday, Nov. 19. That's when Earth will pass through the center of a stream of comet debris laid down by Tempel-Tuttle in 1866. For much of North America, the Leonids radiant will be high above the south-southeast horizon during that same 1866 stream encounter.

Much of Europe and western Africa are favored for the first Leonid outburst, scheduled to peak within a few minutes of 0400 GMT on Nov. 19. Based on a consensus of several Leonid forecasts the entire outburst from the rapid climb to the peak followed by an equally rapid decline should last about 100 minutes.

The best views will be over central Europe and west-central Africa (only in the north), where the Leonid radiant will be high in the south-southeast sky, while the bright Moon is low in the west. It will also be around this time that dawn will break with morning twilight slowly brightening the sky.

The second Leonid outburst will come during the daytime for Europe and Africa and will be primed chiefly for North Americans. The peak is expected to come within a few minutes of 5:35 a.m. EST (subtract one hour for the Central Time zone; two hours for Mountain; three for Pacific). Based on a consensus of several Leonid forecasts this second outburst should also last about 100 minutes from start to finish.

Sprinkles of shooting stars will occur in the hours surrounding the predicted peaks, and viewers should be aware that the times could vary. Brief outbursts can occur at any time.

Only near and along the Atlantic seaboard will advancing morning twilight become an issue. The farther to the east one goes, the brighter the dawn sky will be. Along much of the U.S. East Coast, peak Leonid activity is due to occur during various stages of astronomical twilight, meaning that the eastern sky will be brightening, but many relatively dim stars -- third and fourth magnitude in an astronomers terms -- should still be visible under skies without significant local light pollution.

Over the Maritime Provinces of New Brunswick, Nova Scotia and Prince Edward Island, nautical twilight will be in progress: the fainter stars will have faded away, but most first and second magnitude stars should still be readily visible. But for Newfoundland, civil twilight will be underway; meaning that even the brightest of the stars will probably be invisible. Aside from the Moon, the only other objects that will likely still be evident will be Jupiter and Venus.

Moreover, for eastern North America, where the peak of the shower is forecast near the break of dawn, the Leonid radiant will appear to stand high in the south-southeast, while the Moon sits low down toward the west. Roughly near and along longitude 82W, the predicted time for the second outburst is also scheduled to coincide with the beginning of astronomical twilight.

Along this line from southern Canada, south to the Gulf Coast, the bright Moon will appear to stand 10 above the west-northwest horizon just as the eastern sky begins to get bright. To get an idea of how large 10 is, make a fist and hold it at arms length. Now, the width of your fist will be equal to roughly 10.

So, the fact that the Moon will be so low in the sky suggests that easterners might try to "hide" it from view. Blocking it behind some trees or a house will certainly be helpful. Even better would be something larger such as a high mountain, to caster a larger and deeper shadow over your entire surrounding landscape.

Yet another possibility would involve some extreme cooperation from Nature, a line of thick clouds approaching from a westerly direction ahead of an approaching storm. The clouds would cover the Moon, but hopefully not be moving so fast so as to cover up the rest of the sky as the Leonids are reaching their peak.

Farther to the west, trying to hide the Moon wont be very practical, as it will be much higher up in the sky. Along the West Coast of the United States, both the Moon and the Leonid radiant will be pretty much at similar altitudes above the horizon (about 40 up); the radiant will be in the east-southeast, while the Moon will be over in the west-northwest.