[TWIAR] Surprise Meteor Shower Possible in June

[Greg Williams]

Probably too late to air for TWIAR, but it might be noted for Field Day next
weekend.
Greg

By Joe Rao

SPACE.com's Night Sky Columnist, SPACE.com

Meteor enthusiasts will likely be out in force in the coming nights, hoping
to catch a glimpse of an on-again, off-again meteor display. Special
emphasis will be placed on two specific nights: June 22-23 and June 26-27.

Ironically, the month of June is usually not noteworthy for any major meteor
showers.

Yet six years ago, during the final weekend of June 1998, sky watchers
worldwide were caught off guard by an unexpected shower of bright meteors
and fireballs.

>From Japan, for instance, came reports of meteors that were visible even
through heavily overcast skies. Reports from visual observers in other
regions suggested that this surprise meteor display produced meteor rates of
anywhere from 50 to 100 per hour and lasted more than half a day.

Similar bursts of June meteor activity were noted many decades ago, in 1916,
1921 and again in 1927. Because the meteors seemed to fan-out from a region
of the sky near the northern border of the constellation of Bootes, the
Herdsman, they became popularly known as the "June Bootids."

Comet bits

It was also in 1916 that the legendary British meteor observer, William
Denning, first suggested that these meteors were bits and pieces shed by the
Comet Pons-Winnecke, a rather small, dim object and a member of the Jupiter
family of comets. Such comets are so-named because they have their aphelia
the point in their elongated orbits that place them farthest from the Sun at
roughly the same distance of the planet Jupiter.

The orbits of the Earth and the comet were relatively close to each other
during the early 20th Century.

In fact, Pons-Winnecke's closest point to the Sun its perihelion slowly
shifted from just inside the Earth's orbit in 1916 to just outside it during
1921 and 1927.

Astronomers assumed that it was this close proximity between the two orbits
that accounted for the enhanced meteor activity seen in those three years.

But since then, due to a series of relatively close encounters with
Jupiter's powerful gravitational field, the orbit of the comet has
significantly changed.

Since 1921, the gap between the orbits of the Earth and the comet has been
gradually increasing, becoming more than 22 million miles (35 million
kilometers) by 1998.

Because of this large gulf between the two orbits, it seemed logical to
believe that any future enhanced meteor activity from Comet Pons-Winnecke
would be all but impossible. That argument certainly held up until June
1998. How then, could that meteor shower have taken place with the two
orbits so widely spaced?

The answer came from astronomers David Asher of Armagh Observatory in
Ireland and Vacheslav Emel'yanenko, of South Ural University, Chelyabinsk,
Russia. Their studies showed that the 1998 meteors were the result of
meteoroids released from Comet Pons-Winnecke back in the year 1825.

Asher and Emel'yanenko pointed out that the planet Jupiter completes one
orbit around the Sun in the same time that it takes the meteoroids shed from
Comet Pons-Winnecke to complete two. In other words, while Jupiter takes 12
years to go around the Sun, the meteoroids from Pons-Winnecke take 6 years;
a 2 to 1 ratio. So instead of spreading around the whole orbit, the
meteoroids were kept clustered closely together by Jupiter's gravitation.

Computer simulations by Asher and Emel'yanenko also demonstrated that the
comet and its ejected particles from 1825 were apparently disturbed by
Jupiter in different ways, so that in the ensuing years the comet and the
particles that it shed became widely separated from each other.

Ultimately, however, in June 1998, the meteoroids ended up cutting right
through the Earth's orbit, producing the unexpected bevy of bright meteors.

Another good shower?

So if the meteoroids that produced the bright 1998 display are still
basically moving around the Sun in a 6-year orbit, does that mean that we'll
be in for a repeat performance in 2004? Viewpoints are mixed.

Jrgen Rendtel, president of the International Meteor Organization, believes
that 2004 could be another good year to look for the June Bootids.

Rendtel points out that on Sunday, June 27 at 01h GMT (which corresponds to
Saturday, June 26 at 9:00 p.m. EDT) the Earth should be passing through
essentially the very same region of the meteoroid stream as in 1998.

That time would be the middle of the peak activity seen in 1998, but since
that display lasted for many hours, observers worldwide should stay alert
through Saturday night on into Sunday morning for any unusual or enhanced
meteor activity.

On the other hand, David Asher's belief is that little or nothing will be
observed, based primarily on the simple argument that unusual numbers of
bright meteors should also have been seen in 1992 and 1986, but nothing
apparently occurred.

In recent days, a different forecast for the June Bootids has been issued by
Jerimie Vaubaillon of the Institut de Mcanique Cleste et de Calcul des
phmrides, in Paris, France and Russians Sergey Dubrovsky and Sergey Shanov.

Their calculations suggest that the Earth will interact with a swarm of
meteoroids that were ejected by Comet Pons-Winnecke at not just one, but
several of its past visits to the Sun, most notably in 1819, 1825, 1830,
1836 and perhaps 1875. In addition, the predicted peak for this activity
comes several days earlier than Rendtel's suggestion: Wednesday, June 23 at
11h GMT (7 a.m. EDT).

Western North America and the Pacific Ocean will still be in darkness at
that time, and are favored with the best possible views. But should the
activity last for many hours, then it could be worthwhile to carefully watch
the sky from Tuesday night, the 22nd, on until the first light of dawn on
Wednesday, the 23rd.

Whether you plan to look for the June Bootids on the night of June 22-23 or
again on the night of June 26-27, keep in mind that the constellation of
Bootes will be excellently positioned as darkness falls. It will appear
nearly overhead and high up in the northern sky and will remain in view
through the night as it descends toward the northwest.

Fortunately, the Moon will be a rather wide crescent and will set just
before midnight (local daylight time) on the night of June 22-23. It will,
however, be more of a hindrance on the night of June 26-27 when it will have
increased in brightness to a bright gibbous phase and not setting until
after 1:30 a.m.

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Gregory S. Williams
Webmaster
This Week in Amateur Radio
k4hsm at twiar.org
http://www.twiar.org
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