8:30 AM | *Possible rare outburst of meteors just before midnight in the eastern US*

This map from Sky & Telescope shows the sky facing southeast from Philadelphia at 11:50 p.m. EST on Nov. 21, when the rare Alpha Monocerotid meteor shower will have a very brief outburst. Two Alpha Monocerotid radiants are marked, 1985 and 1995. (Image credit: Sky & Telescope)

Overview

There is a chance that they’ll be a burst of meteors later tonight as the Earth passes by a stream of debris from an unknown comet.  The outburst could last as little as 15 minutes and probably no more than 40 minutes, but it could result in dozens of meteors during a short time period beginning somewhere between 11:30 -11:50 PM.  There is no guarantee that anything will happen as only a handful of outbursts have been observed in the past century from this particular debris field with the last one being in 1995 and, as is often the case around here, cloud cover will be a concern.

“This is a composite of alpha Monocerotids detected in low-light video observations by Sirko Molau in Germany during the 1995 outburst,” says Jenniskens of NASA/Ames (courtesy NASA, spaceweather.com).

Details

Only a handful of Alpha Monocerotid outbursts have been observed in the past century which means researchers are still mapping the debris zone.  Earth could hit an extra-dense spot resulting in an impressive display later tonight or could pass through a void resulting in a dud. No one knows exactly where the Alpha Monocerotid meteors come from as the parent comet has never been seen.  Based on the dynamics of the debris, it probably circles the sun every 500 years or so.  We know the comet exists only because of the dense, but exceedingly narrow (~26,000 miles) trail of dust it left behind long ago.  Earth has run into the dust trail at least 4 times, causing bright outbursts of meteors in 1925, 1935, 1985 and 1995.

The best viewing for this possible event will be in western Europe as for them, anything that takes place will be relatively high in the southern sky. Skywatchers in the eastern part of North America can see the show as well, but not quite as easily.   The Monoceros (Greek name for “unicorn”) constellation near Orion the Hunter will be hugging the east-southeast horizon when the potential meteor shower peaks over the east coast of the US and Canada. 

There is some reason for hope this year as some forecasters suggest the Earth will pass about as close to the debris field as it did in 1995 when the meteor shower outburst was very impressive with an hourly rate of around 400.  Also, the brightness of the moon isn't expected to interfere since it will be waning.  Unfortunately, not only is there the “iffiness” of the meteor outburst itself, but cloud cover could become an issue as later tonight, it’ll likely become mainly cloudy in much of the Mid-Atlantic region.  If a “1995-type of outburst” should happen to repeat itself tonight, skygazers can expect to see around seven meteors per minute and they’ll be moving at more than 140,000 miles per hour.  Most of the meteors in the 1995 outburst ranged in magnitude from +2 to +0.

Meteor outbursts are hard to predict and there’s no guarantee that this one will materialize and that the skies will be favorable.  But if it does deliver, it could be quite dramatic.  Go out a bit early in case it begins earlier than expected as published predicted started times have actually varied from 11:15 to 11:50 PM - look towards the east-southeast horizon.  One final note for skywatchers, the sunset sky is about to become pretty spectacular in its own right. Venus and Jupiter are converging for a close encounter in the evening twilight that will decorate the southwestern horizon for the rest of November.

Venus and Jupiter will be visible near sunset for the rest of November in the southwest sky; image credit spaceweather.com

First-hand accounts of prior outbursts from “space.com”

The first known Alpha Monocerotid outburst came in 1925, when late on the night of Nov. 20, F.T. Bradley of Crozet, Virginia, caught sight of 37 meteors in just 13 minutes. He ran inside to get star charts for plotting the paths of the meteors and resumed his observations 10 minutes later, but didn't see another meteor. Without plotting any of the previously seen meteors, Bradley estimated that they emanated somewhere below the Orion constellation. Another witness was noted meteor expert Charles P. Olivier, who was working in the observatory at the University of Virginia. Stepping outside for only a few moments and scanning the sky, he caught sight of "three bright meteors" within just a minute.

Ten years later, in 1935, during the early hours of Nov. 22, professor Mohd. A.R. Khan from Begumpet, India, witnessed a "fine shower of meteors" emanating from the constellation of Monoceros, the Unicorn. In just 20 minutes he counted over 100 meteors, which quickly dwindled to 11 in the next 20 minutes. At the same time, the commanding officer of the USS Canopus, then anchored in Manila harbor, saw meteors at the rate of 2 per minute during a 30-minute interval.

After being dormant for half a century, the Alpha Monocerotids came to life again on the morning of Nov. 21, 1985, for two observers in California. Keith Baker, a night assistant at the Lick Observatory counted 18 meteors in just 7 minutes coming from a region near Canis Minor. And from Capitola, Richard Ducoty saw 27 meteors in 4 minutes, before this burst of activity rapidly trailed off to nine during the next 14 minutes. He commented that the brightest meteors ranged from 0 to negative 2 magnitude (as bright as Jupiter), also noting that their speed was quite fast, a little slower than the Leonids.

Assuming that the shower would rev up again in 1995, Jenniskens published an announcement in WGN, the Journal of the International Meteor Organization, alerting prospective observers of a possible outburst of Alpha Monocerotid meteors. Europe was in the favored viewing zone. Jenniskens and members of Dutch Meteor Society, chose the Calar Alto Astronomical Observatory located in Almería Province in Spain to watch for the expected meteor show.  

"Suddenly, around 0:10 UT, three meteors radiated from a point on the border of the constellations Canis Major and Monoceros, 15° away from the position (radiant) given in past accounts. And this time it did not stop after just a few. Meteors started pouring out of Canis Minor, falling left and right, up and down. Bright meteors too. By 1:29 UT meteors were falling at a rate of five or more per minute. Twenty minutes later it was all over. Emotions were strong when the stream peaked that night on Calar Alto, and we broke down in tears." 

Considering that over the past century, three of the four outbursts were unexpected and seen by so few people Alpha Monocerotid displays may have happened in other years without ever being noticed.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com