We've talked about this before in year's past - a couple of times. It seems like each time we start to get excited about seeing some neat celestial event, such as a storm of meteors, when the big day arrives, it's dudsville. I've been disappointed lots of times, but I guess that's one of the reasons that makes actually seeing something extraordinary so special. This weekend and especially early Sunday morning, the Leonid meteor shower may erupt, from what is usually a drizzle of meteors, to produce a meteor storm where hundreds an hour may be observed.

They won't be seen everywhere in the world, even if this turns out to be a major storm, but if they're anything like the last big Leonid meteor storm that bedazzled much of the US in November of 1966, they shouldn't be missed. Ok, so you have to get up in early in the morning hour on a cold night in the chance that something will come off, but what else do you have to do on a Saturday night (I guess my social life could use a bit of a lift), and if there's nothing to be seen, you can at least go back inside and rack out since it's not a work or school day. In fact, this meteor shower is being pretty generous; it's occurring on a weekend night, there won't be any interference from the moon (it'll be almost new - 2 days old), and the forecast, as of Wednesday, indicates that dry, nearly cloudless weather should continue over the eastern 2/3 of the country through the coming weekend.

Every year around November 17th, Earth's orbit carries us though the Leonid meteor stream - so named because most of the meteors come from the direction of the constellation Leo the Lion. Within the overall meteor stream are a number of smaller streams or ribbons, having a greater density of dust and cometary debris. The parent comet responsible for the Leonid meteors, Comet Temple-Tuttle, returns to perihelion (closest to the Sun) every 33 years or so, generating a new trail of meteoroids and dust each time. The closer the Earth is too the comet, after it has crossed our orbit, the better the chance that a meteor storm will occur. Temple-Tuttle was closest to the Sun in 1998 and brief meteor storms were visible in parts of Asia, and parts of Europe, the Middle East and Africa in both 1998, 1999 and in 2000. However, it's thought that the Earth may encounter a dense ribbon of meteors again this year. We'll essentially be getting leftovers, but this is the leftover season (Thanksgiving is coming up next week), and on occasion, leftovers are as good as the original.

So this may be the real deal. Scientists who study meteors are predicting that this year's Leonid shower will be the best in the US since the storm of 1966. Don't expect for it to rival the 66' storm, when as many as 100,000 per hour were witnessed by people in the southwestern states. The benchmark for all meteor storms in the US is probably the 1833 Leonid meteor storm, when people were said to be awakened from their sleep by the light of meteors streaming across the night sky. Keep in mind, however, like weather forecasting, meteor forecasting isn't always reliable. Compared to weather data, which are collected in many places around the world every hour, scientists have very little hard data about meteors. Meteor forecasting is still in its infancy. For example, it's not known how fast meteoroids are ejected from the parent comet, nor does anyone really know the density of the ribbons that generate the bulk of the meteors. Nevertheless, this year's Leonid could be worth staying up for.

Several different models are used for meteor forecasting. In 1999, a number of the models agreed and the actual observations weren't too far off from what the models predicted, but this year, the models aren't so close. Because of the orbital characteristics of the Earth and Temple-Tuttle in 1999, only one major meteor stream would play a role in what we could observe. The big problem this year, is that the Earth is considerably further from Comet Temple-Tuttle, and we'll be near a number of different streams, some that produced storms more than 200 years ago.

According to models developed by four meteor forecasters, the following is a list of cities and what the different models say about what we can expect this coming Sunday morning - for very clear and very dark sky conditions. The numbers are the total that may be seen every 15 minutes, and only values for the models predicting the most and the least number of meteors are given.

Albuerqueque, New Mexico - maximum number to occur between about 3:30 and 4:30 a.m., most predicted (683), least predicted (41)

Atlanta, Georgia - maximum number to occur between about 5:00 and 6:00 a.m., most predicted (855), least predicted (50)

Bangor, Maine - maximum number to occur between about 5:15 and 6 :15 a.m., most predicted (467), least predicted (7)

Cleveland, Ohio - maximum number between about 5:00 and 6:00 a.m., most predicted (841), least predicted (49)

Miami, Florida - maximum number between about 5:30 and 6:30

Minneapolis, Minnesota - maximum number to occur between about 3:30 and 4;30 a.m., most predicted (762), least predicted (45)

New Orleans. Louisiana - maximum number to occur between about 5:00 and 6:00 a.m., most predicted (825, least predicted (48)

Portland, Oregon - maximum number to occur between about 2:20 and 3:30 a.m., most predicted (521), least predicted (32)

Sacramento, California - maximum number to occur between about 2:30 and 3:30 a.m., maximum predicted (531), minimum predicted (32)

St Louis, Missouri - maximum number to occur between about 4:30 and 5:30 a.m., most predicted (804), least predicted (47)

Salt Lake, Utah - maximum number to occur between about 3:00 and 4:00 a.m., most predicted (627), least predicted (38)

Washington, D. C. - maximum number to occur between about 5:00 and 6:00 a.m., most predicted (873), least predicted (39)

The number '873' for Washington, when multiplied by 4 gives a value of 3,492 meteors per hour! It's tempting to think that this is how many you'll see. Remember, though, this is from the model that's predicting the highest number of meteors, and many, perhaps most, of these meteors will be missed if you don't have a very dark sky for a backdrop.

From the above, you can see that there's a big spread between the most and the least predicted, so the confidence isn't very high. The Earth is expected to interact with several meteor streams during about an 8-hour period. Of course, only those places experiencing nighttime when we enter the streams can see the meteors. This means that this year, Europe, Africa, western Asia, and eastern South America will miss most of the action. It's thought that less than 1/2 of the Earth will have a chance to see the big show.

Since North America will be in darkness when it's predicted that the Earth will enter at least one of the streams, most of the US should have a pretty good chance to see a decent number of meteors. However, it appears that the Middle Atlantic, Mid Western, and Southeastern states may be slightly better positioned than the Western and Northeastern states. The best time to observe the meteors is close to dawn in the east but several hours before dawn in the west. Considering all factors, it seems that the absolute prime viewing locations will be in Australia, the Pacific Islands and eastern Asia. They'll likely be exposed to the densest meteor stream when its darkest (on the morning of November 19). A cautionary note for those of us who live in the eastern US, if the stream occurs later than predicted, we'll be in morning twilight, and could miss the whole thing. Let's keep our fingers crossed, and remember, like the lottery, you can't win if you don't play the game.

For more about this see the Earth Science Picture of the Day for November 15 and 16
http://epod.usra.edu/
and the International Meteor Organization
http://www.imo.net/
and also the Armagh Observatory
http://www.arm.ac.uk/leonid/index.html