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Astro-Event: Don’t Miss the Geminids!

Astro-Event: Don’t Miss the Geminids!

Originally posted on the 10th December 2010 by AstroGuys


Looking Northeast at about 10 PM. (Photo by Author).

   This year, believe the hype; this month’s Geminid meteor shower is a sure bet. This shower is one of the few dependable ‘old faithful’ meteor showers of the year. Peaking on the night of December 13th-14th, this year’s apparition sees a well placed northern radiant rising high in the northeast as the first quarter Moon sets about midnite local. The Geminid stream radiates from very near the bright star Castor in the zodiac constellation Gemini the Twins and typically produces up to 100 to 120 meteors per hour. If you are placed in mid-northern latitudes, you may see some activity shortly after sunset, but the real meteoritic action will begin after midnite. Think of a car driving at night in a snowstorm, not a stretch in the depths of the northern hemisphere winter. Looking forward into your high beams you get the cool vintage “Star Trek” effect, as you and your vehicle plow headlong into the stream of snowflakes. Think of the flakes as meteors and the car as the Earth; we face headlong into the meteor stream after midnight, and hence see more flashing meteor trains. The Geminids present several swift movers and fireballs, and the darker skies you have access to, the more you’ll see. Be sure to dress warm (it is winter out there!) and make a point to count and record your observations. Meteor shower observing is one of the few remaining scientific endeavors that remains low tech. Also, don’t forget to participate in the #meteorwatch via Twitter! This shower has a broad peak, and will be active the week of December 12th until the 18th, when the solstice-centered Ursids become active. In fact, there are some indications that the Geminids have been increasing in activity over the past decade, and certainly there’s a lot of material out there. The predicted peak centers on 5:00 AM UTC, just past midnite Tuesday morning from the US East Coast. And if that weren’t enough, it’s one of the last meteor showers with the Moon placed below the horizon until 2012; only the Quadrantids and Giacobinids have the same favorable geometry in 2011. Good luck, and be sure not to miss this unique meteor shower!         

The astro-term for this week is the Yarkovsky Effect. The parent body that produces the Geminids, 3200 Phaethon, harbors somewhat of a mystery. Discovered in 1983, this space rock has been identified as the source of the Geminid meteor stream.NASA researchers estimate a massive amount of material exists, more than 100 times that of the average meteor stream. Unlike most streams that emanate from comets, however, 3200 Phaethon is an asteroid. Or is it an inactive comet? The mystery deepens, as the color of this strange rock is very similar to another asteroid, Pallas. 3200 Phaeton’s path sees it passing within Mercury’s orbit every 1.4 years, which brings it well within the realm of the Yarkovsky effect. This is the tiny bit of momentum imparted on a rotating body as it re-radiates photons absorbed from the Sun. On large bodies the effect may be negligible, but on tiny asteroids it can produce major changes in orbit over time. In fact, employing the Yarkovsky Effect by changing the reflectivity of an Earth-crossing asteroid is one way of possibly deflecting a lethal space rock. Is 3200 Phaethon a dormant comet or the remnant of an asteroid belt break up? This is one worldlet that definitely begs future exploration.      

Adventures in Meteor Spotting


Meteor observing is a favorite sport of ours. Unlike other astronomical endeavors, observing and recording meteor showers requires minimal gear; just a good pair of eyes and an intimate knowledge of the sky. And to cap it off, a true meteor storm can be an event of a lifetime… only a total solar eclipse or a good auroral display comes close in the sheer “wow” factor department. As the Perseid meteor shower draws toward its yearly maximum on August 12th, we at Astroguyz have been invited by the organizers of #Meteorwatch to present some tips and tricks of the meteor observing trade, as well as share some personal ramblings and trivia we’ve featured over the years as well as new insights sent in by our readers.


We have a special fondness for the Perseids, as observing them was a yearly family tradition growing up in northern Maine. Our backyard skies were pristine and dark, the kind that folks today might drive over 100 miles to camp under. The Perseids occurred until warm summer skies, and we would simply lay back on lawn chairs in sleeping bags as the sky wheeled slowly above us. The Perseids are sort of an “old-faithful” of meteor showers, as they perform reliably every year. Normal rates are about 60 per hour, although these have been greatly enhanced since the perihelion passage of the progenitor comet Swift-Tuttle in 1992. The 2009 Perseids approached levels of 200 per hour, and sported multiple successive peaks. Be wary of popular news outlets that will parrot “The meteor storm of a lifetime!” as this has joined the Mars email hoax in its yearly August run. The good news for the Perseids is that this year they’re nearly exactly timed with the New Moon, which occurs on August 10th. The darker the skies that you can position yourself under, the more meteors you’ll see.


But first, some meteor observing lingo. The gold standard for determining the intensity of a meteor shower is termed the Zenithal Hourly Rate. The ZHR is an ideal number, the number of meteors you’ll see under absolutely dark skies if the radiant of the shower is directly over your viewing location and you have complete 360° all-sky coverage. This, of course, never happens in reality. Ways to maximize this number in actuality include using multiple observers to view in different directions (three is optimal) and choosing a good dark sky site. If the Moon is above the horizon, try and place it behind a building or object and view in the opposite direction.


Meteors will also occasionally approach from other directions, known as sporadics. The rates for these can vary throughout the year and tend to hover between 1-5 per hour. Some sporadics may be related to other showers, while a handful come in from the apex, antihelion (anti-sunward) and toroidal points on the celestial sphere. For example, fainter showers such as the Kappa Cygnids, Delta Aquarids, and the Alpha Capricornids may all be sighted during the Perseids. Make a careful note of the direction of travel to discern any stragglers.


Speaking of which, meteor observing is one of the last fields of endeavor that a naked eye observer can contribute useful scientific information to. Simply note your location, period of observing time, and how many meteors you spotted. Other useful bits of data include the limiting magnitude from your viewing sight (the Bortle Scale is a good way to quantify this) and method used. Some observers note the magnitude of each meteor observed and its direction of travel, their thoughts and feelings, etc… but I find a simple “where/how many/how long” method is best. Remember, you want to keep those dark adapted eyes on the sky, not entering notes. The best method is to simply record your observing session for later analysis; I’ve used a small digital recorder for this task to great effect. Smaller than a cell phone, it can record spoken impressions for hours. Just remember to mark your start time when recording. Another helpful tool to plan your observing sessions is the program Meteoracle. This runs on your desktop/laptop and forecasts what you might see based on your input location. Keep in mind, however, that this is not a live forecast, merely a projection. I’d like to see them take the next step and incorporate weather conditions and current reports of meteor activity into the mix to see how the forecast is evolving from day to day.


Organizations such as the International Meteor Observers group take and compile reports from observers around the globe. If you are lucky, you just might be the only observer reporting from your wind-swept longitude in the Arctic Tundra or the Gobi desert and manage to provide that crucial piece of data. We were lucky in this aspect to catch the Leonid meteor storm in 1998 from the deserts of Kuwait while deployed with the USAF. That particular year, most northern hemisphere longitudes were either clouded out or missed the peak as it occurred during broad daylight. Storm levels approached a ZHR of +1,000, with a bright fireball every several seconds.


The Leonids are the most infamous of all showers, with ZHR peaks approaching 10,000 every 33 years. In 1966, observers reported a distinct sense of the Earth’s forward movement through space, much like the old Star Trek “warp-drive” effect. In 1833, this same shower awoke startled villagers on the US Eastern Seaboard, convinced the apocalypse was nigh! Needless to say, the Leonids are always worth keeping an eye on every year around November 17th, and will start to gear up again in 2030.


Other showers known for this outburst style of activity include the Giacobinids, also known as the Draconids (October 8th-10th), the Ursids (December 22nd/23rd), and the Bootids (June 26th to July 2nd). Other ‘old faithful’ style annual showers include the Quadrantids (named after an obsolete constellation, Quadrans Muralis, or the mural quadrant), the Lyrids, and the Geminds. The Geminds are also unique in that their progenitor body is asteroid 3200Phaethon. This is thought to be perhaps an inactive comet nucleus. One shower, dubbed the daytime Arietids, was only discovered with the advent of radio astronomy, and would be well known if only it didn’t occur in the broad daylight. The aforementioned Giacobinids are also unique in that their radiant is high in the sky for northern hemisphere observers, and actually peaks before midnite. This usefully lackluster shower also bares careful scrutiny as it has been known to outburst on occasion, most notably on the years 1933, 1946 and 1998. There is some stir in the meteor observing community of a possible outburst in 2010 or 2011…


Some mysteries still abound surrounding all things meteor and meteorite related… for example, a hot debate exists concerning the appearance of “corkscrew” meteors. Such apparitions defy the laws of physics, and yet even seasoned observers report them. Either there is something about meteor trajectories that we do not understand, or a very clever optical illusion is occurring.


Another phenomenon that has considerable precedent is audible meteors. I once witnessed this bizarre trait during a particularly bright Perseid; it actually produced an audible hiss! This phenomenon has been dismissed as an illusion until the last few decades. Recent research has lent some credence to idea that under the right conditions, a bolide may produce very low frequency radio emissions and cause localized electrophonic sound to reflect off of wires, flag poles, or even fields of grass or trees. Popping or crackling may also occur. Particularly interesting is the fact that these sounds occur nearly simultaneously with the sighting, and thus cannot be related to sound waves traveling from the meteor. And of course, it is not completely understood why an inordinate number of meteor shower radiants occur in the northern celestial hemisphere!  


Still want more?  Conducting photography during a meteor shower is simple; simply aim your tripod mounted DSLR camera at or near the radiant, focus, lock the shutter open, and let the meteors “burn in” as they pass overhead. Some astronomers have built 360° degree all-sky cams which record the sky continuously, equipped with the same technology as low light surveillance cameras. Some observers even monitor meteor showers in the radio end of the spectrum. This can even be done with a simple FM radio; set it to an unused frequency, and you may hear a distant station fade in and out as the signal is briefly reflected off of the hot ionized trail left by a meteor.


Finally, a fascinating method of collecting micro-meteoroids has come to our attention. Some enterprising folks have managed to collect tiny specimens via magnets and rain gutters…the thinking goes that tiny ablated spherules stay suspended in the atmosphere and make their way down as cosmogenous material during rain showers. The trick is to have a huge collection area and a powerful magnet. Other metallic particles from volcanic ash or terrestrial pollution may be present, but micrometeorites reveal themselves as tiny black spheroids under a microscope. I was highly skeptical of this when I first heard it, but now have a set of rare earth magnets enroute to Astroguyz HQ to test this theory out… and here we thought we’d heard of everything


I hope this short smorgasbord of all things meteor-related has served to whet your appetite for more. Meteor shower observing is one of the simplest yet most rewarding endeavors you can pursue in astronomy, and it always seems to have the biggest wow factor with the general public. Have fun, and clear skies!              



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