Remnants of Halley's Comet Rain Down
By Joe Rao,
Posted: 2007-10-20 21:30:28
Filed Under: Science News
Space.com
(Oct. 19) -- A junior version of the famous Perseid meteor shower is scheduled to reach its maximum before sunrise on Sunday morning, Oct. 21. This meteor display is known as the Orionids because the meteors seem to fan out from a region to the north of Orion's second brightest star, ruddy Betelgeuse.
After peaking Sunday, activity will begin to slowly descend, dropping back to around five per hour around Oct. 26.
Photo Gallery: Meteors Light Up Sky
AP Graphic
The Orionid meteors seen falling this weekend are believed to result from the orbit of the famous Halley's Comet, shown above in a graphic.
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Weather permitting and under very dark skies away from light pollution, skywatchers could see several meteors per hour. Rates will be significantly lower in cities and suburban areas.
Interestingly, this year, brilliant Mars is nearby and the apparent source of these meteors, called the radiant, will be positioned roughly between Mars and Betelgeuse.
When and where to watch
Currently, Orion appears ahead of us in our journey around the Sun, and has not completely risen above the eastern horizon until after 11:00 p.m. local daylight time. Expect to see few, if any Orionids before midnight – especially this year, with a bright waxing gibbous Moon glaring high in the western sky.
But moonset is around 1:30 a.m. local daylight time on Sunday, and that's a good time to begin preparing for your meteor vigil. At its best several hours later, at around 5:00 a.m. when Orion is highest in the sky toward the south, Orionids typically produce around 20 to 25 meteors per hour under a clear, dark sky.
"Orionid meteors are normally dim and not well seen from urban locations," said meteor expert Robert Lunsford, adding, ". . . it is highly suggested that you find a safe rural location to see the best Orionid activity."
Photo Gallery: Amazing Space Photos
Reuters / NASA
A volcano on the north pole of Jupiter's fourth largest moon, Io, spews a giant plume of dust 200 miles into space.
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According to Lunsford, Orionid activity has been increasing noticeably since Oct. 17 when they were appearing at roughly five per hour in dark-sky conditions. The last stragglers usually appear sometime in early to mid Nov.
Halley's Legacy
In studying the orbits of many meteor swarms, astronomers have found that they correspond closely to the orbits of known comets. The Orionids are thought to result from the orbit of Halley's Comet; some of the dust which has shaken loose from this famous object as it runs its gigantic loop from the Sun out to Neptune, ram our atmosphere to create the effect of these "shooting stars." The comet, which can be seen every 75–76 years, last passed by Earth in 1986.
There are actually two points along Halley's path where it comes relatively near to our orbit.
One of these points corresponds to early May and causes a meteor display that emanates from the constellation Aquarius, the Water Carrier. The other point lies near the late October part of our orbit and produces the Orionids. In May we meet the "river of rubble" shed by the comet on their way outward from their nearest approach to the Sun, while in October we encounter the part of the meteor stream moving inward toward the Sun. The meteors are moving through space opposite or contrary to our orbital direction of motion. That explains why both the Aquarids and the Orionids hit our atmosphere very swiftly at 41 miles (66 kilometers) per second – only the November Leonids move faster.
Another distinguishing characteristic that the October Orionids share with the May Aquarids is that they start burning up very high in our atmosphere, possibly because they are composed of lightweight material. This means they likely come from Halley's diffuse surface and not its core.
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What to expect
Last year, there was an unexpected surprise when the Orionids put on a display more worthy of the Perseids. Observers saw meteors falling at double the normal rate, or 40 to 50 per hour. In addition, many Orionids were much brighter than normal; a few even rivaled Venus in brilliance.
Two meteor researchers, Mikaya Sato and Jun-ichi Watanabe of Japan's National Astronomical Observatory, recently announced in a paper released by the Astronomical Society of Japan that the unusual concentration of large particles that produced last years Orionids, were probably ejected from Halley's Comet almost 3,000 years ago and are being held together by interactions with Jupiter about every 71-years.
Apparently, there may also have been unusual Orionid activity during the years 1933 through 1938, so perhaps after an absence of seven decades this concentration of comet material has returned, implying another rich Orionid display might be in offing this year.
The only way to know is to step outside just before the break of dawn on the morning of Oct. 21 (try the mornings of Oct. 20 and 22 as well). Almost certainly, you should sight at least a few of these offspring of Halley's Comet as they streak across the sky.
The Orionid Meteor Shower: See the Legacy of Halley's Comet
By Joe Rao
SPACE.com Skywatching Columnist
posted: 13 October 2006
06:11 am ET
It has been 20 years since Halley's comet last passed through the inner solar system. This famous comet takes roughly 76 years to circle the Sun. Perhaps you remember seeing the comet for yourself through binoculars or a telescope, or maybe you participated in a tour that took you to some exotic locale south of the equator where you could get a naked-eye view of the comet climbing high into the sky.
Or maybe, because of light pollution or the comet's low altitude above the horizon you didn't see Halley at all. If you missed out on the 1986 event, you have two options:
* Wait and hope that you'll be around when the comet makes its next return during the summer of 2061.
* Step outside before dawn during the next week or so and try to catch a view of some "cosmic litter" that has been left behind in space by Halley's comet.
Halley's comet has left a legacy that is visible to us in the form of two annual meteor showers, one of which will soon be reaching peak activity: the Orionid meteors.
Great year
This will be an excellent year to look for them, since the Moon will be New on Oct. 22, which is right around the time that these meteors will be near their peak, ensuring that skies will be dark.
Comets are the leftovers of the day of creation, the odd bits and pieces of simple gases-methane, ammonia, carbon dioxide and water vapor-that went unused when the Sun and its attendant planets came into their present form. Meteoroids that are released into space out of this cometary debris are the remnants of a comet's nucleus. All comets eventually disintegrate into meteor swarms and Halley's is well into that process at this time.
These tiny particles-mostly ranging in size from dust to sand grains-remain along the original comet's orbit, creating a "river of rubble" in space. In the case of Halley's comet, which has likely circled the Sun many hundreds, if not thousands of times, its dirty trail of debris has been distributed more or less uniformly all along its entire orbit. When these tiny bits of comet collide with Earth, friction with our atmosphere raises them to white heat and produces the effect popularly referred to as "shooting stars."
The orbit of Halley's comet closely approaches the Earth's orbit at two places. One point is in the early part of May, producing a meteor display known as the Eta Aquarids. The other point comes in the middle to latter part of October, producing the Orionids.
When to watch
The best time to watch begins from 1 or 2 a.m. local daylight time until around dawn, when the shower's radiant (in Orion's upraised club, just north of the bright red star, Betelegeuse) is highest above the horizon. The higher the radiant, the more meteors appear all over the sky. The Orionids are one of just a handful of known meteor showers that can be observed equally well from both the Northern and Southern Hemispheres.
The Orionids are one of the better annual displays, producing about 15 to 20 meteors per hour at their peak. Add the 5 to 10 sporadic meteors that always are plunging into our atmosphere and you get a maximum of about 20 to 30 meteors per hour for a dark sky location.
Most of these meteors are relatively faint, however, so any light pollution will cut the total way down.
The shower may be quite active for several days before or after its broad maximum, which may last from the 20th through the 24th. Step outside before sunrise on any of these mornings and if you catch sight of a meteor, there's about a 75 percent chance that it likely originated from the nucleus of Halley's comet.
A few Orionids may appear as early as Oct. 9 and as late as Nov. 7. In 1993 and again in 1998, maximum activity unexpectedly came early, on the night of Oct. 17-18. "The activity is not constant from year to year," notes Russian meteor expert, Dr. P.B. Babadzhanov. "The time of maximum shifts significantly and there are secondary maxima."
"They are easily identified . . . from their speed," write David Levy and Stephen Edberg in Observe: Meteors, an Astronomical League manual. "At 66 kilometers (41 miles) per second, they appear as fast streaks, faster by a hair than their sisters, the Eta Aquarids of May. And like the Eta Aquarids, the brightest of family tend to leave long-lasting trains. Fireballs are possible three days after maximum."
Recent studies have shown that about half of all Orionids that are seen leave trails that lasted longer than other meteors of equivalent brightness. This is undoubtedly connected in some way to the makeup of Halley's comet. So it is, that the shooting stars that we have come to call Orionids are really an encounter with the traces of a famous visitor from the depths of space and from the dawn of creation.
